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<--- Don't forget to check out my BLOG while you're here! New content added regularly.
(This article updated regularly due to changes in the industry. Updates will be noted on my BLOG and at the bottom
of this article)
New Tankless Video Series HERE
Tankless 101 A tutorial
for the homeowner and the professional New drain pan for tankless water heaters www.TheWallSaver.com
The Basics Tankless water heaters have been sweeping the nation with a huge growth over the last
5 years or so. These are water heaters that do not have a tank. Many of the larger tankless companies have seen their sales
grow by hundreds of percent each year! These compact units mount on a wall either inside or even outside the house and supply
hot water on demand literally without end! The Europeans have been heating water with tankless heaters for years. Many people
believe that within the next 5 to 10 years 50% or more of all American homes will have a tankless water heater in them! Even
the big tank water heater companies have tried to jump on board by partnering with larger Japanese companies to have units
private labeled for them (More on this later) Tankless water heaters are available in electric natural gas and propane fired
models. The electric tankless water heaters have advantages over tank type electric models but very few provide enough capacity
to serve multiple fixtures with only one unit and may require a larger electrical service to operate them. This has kept
most builders from using them in new construction. Although they do tend work well in small home, condo or apartment applications
where gas is not an option. For the purpose of this tutorial we are going to talk about the gas fired units. Watch for a
future article containing information on electric tankless heaters. Tankless water heaters work on demand by using sensors
and computer boards to monitor the flow of water and change the rate of firing to supply just the amount of hot water required
for the current demand. (They are also called on demand heaters) This means that they burn less gas to supply hot water to
something like a sink than they would if you are using multiple fixtures at the same time. This modulating firing rate also
make them very efficient to operate as you are only using the exact amount of fuel needed at that time. A term that should
be avoided is “instantaneous”. Tankless water heaters are not instantaneous. It does take them about 2 seconds to go from
their at rest “off” mode to producing hot water at the set point temperature. This is not a big issue however. The problem
is if a consumer thinks by hearing the term “instantaneous” that they will get water at every outlet in the house instantly
if they get a tankless heater, they will be disappointed. Most homes have many feet of piping between the water heater and
the outlets and do not have a recirculating system. The amount of time it takes from when a faucet or other hot water fixture
opens to when the set point water gets to that point is called “Lag Time”. In today’s large homes with low flow fixtures
it is not uncommon to see a lag time of over 3 minutes to get hot water to remote fixtures in a home. Changing the type of
water heater will not improve the speed of the delivery of water unless the location of the heater is altered or if a recirculating
system is installed. Because of their small size of course, many times when a tankless heater replaces a tank, it can be
moved to a more central location or nearer to the fixtures it is to serve. This may cut down on the lag time considerably.
Tankless Water heaters save space in a home because they take up NO floor space. They also do not require protection from
vehicles if installed in a garage and are so small they can be installed in a crawl space or attic as well. If you really
need space, many can be installed outdoors giving you all of your interior space back. Just be sure to choose a model designed
for outdoor installation and with freeze protection for your area. (More on this later also) Energy Savings
Tankless water heaters save fuel because they do not have to maintain a supply of hot water in a tank and are typically “always
off”. Tank type heaters fire on and off all the time to maintain the temperature of water in the tank within about 10° -
15° of the thermostat setting. (This is called “Stand-by heat loss”) This also can result in some noticeable temperature
difference. Tankless water heaters provide hot water to the set point temperature plus or minus 2°. Another thing that
makes a tankless hot water heater more fuel-efficient is that they are “fully modulating”. In other words they only use the
fuel needed to heat the water to the set point at the current flow rate. If you are washing your hands using under 1 gallon
per minute (GPM) you will be at a lower firing rate than you would be if you are filling your tub at 3 GPM. This works much
like your car. When you are sitting still the car is idling. When you want to go or go faster you give it more gas and when
you get where you are going you turn it off. With their “always off” condition and their modulating capabilities it is common
to see up to a 50% reduction in fuel use when changing from a tank type heater to a tankless unit. If you are going to
change from a 50-gallon gas heater to a tankless you are probably not going to realize quite that much energy savings. In
fact a 50-gallon tank water heater does not use much more fuel at all compared to most tankless heaters. However a 50-gallon
tank heater only can really give you about 40 gallons of hot water per use before you begin running out of hot water. The
tankless heater will deliver more than 300 gallons per hour for most of the year and you can never run out! If it is an electric
tank water heater that you are replacing, your savings may be higher than 50% depending on the size of the tank. If you really
want to know what your savings may be look for the yellow “Energy Guide” sticker on your existing heater and look for the
one on the tankless unit you are considering. This will give you a good idea of what to expect. Of course your personal
use will effect this as well. If you have a family of 6 that has never had enough hot water with a 50 gallon tank heater,
your bill might just go up because now your family will not be taking cold showers or have to shorten them. If you have a
vacation home that is occupied only on weekends or using the tankless for something like a school locker room, your savings
will be greater because the tankless unit is “always off” eliminating wasted energy. Part of the decision making process
is; What do you want? Endless hot water may be worth the additional investment to you even without an energy payback. Location
Location Location Builders like the tankless water heaters for several reasons, not the least of which is space savings.
When you charge by the square foot for a home, saving space means that home is worth more. A tank type heater installed in
garage requires a floor stand, a pipe to protect against vehicle impact and normally venting all the way to the roof. In
a two-story home, this means more framing, drywall and paint to enclose it. A tankless water heater is wall mounted and can
be sidewall vented, keeping the cost of venting to a minimum. It also does not take up any of the garage floor space. Being
able to install tankless heaters outside or build them into a wall gives even more options that the builder never had before.
This means even less venting cost (practically none) and even more space savings. Some builders will locate them centrally
in a crawl space to cut down on lag time. Others will locate them near a master bath or kitchen. Some will install them
in attics or outside to free up more space. Since there is no tank to burst, installing a tankless heater in an attic is
not as risky as installing a tank there. Even with a drain pan, a tank water heater in an attic is a catastrophe waiting
to happen! A drain pan that is 3” deep will not do much good if the bottom blows out of a 50-gallon or larger tank water
heater. (This is not an uncommon occurrence!) Outdoor Installation Many of the better tankless companies
have models that can be installed outdoors. This frees up all of the interior space and does away with venting costs or combustion
air issues. These units will have their own freeze prevention systems however you will need to protect your water piping
from freezing. This can be done with a pipe cover kit or recessed wall box, which can be insulated. It is also recommended
that you install self-regulating heating cable on the piping to keep it above freezing. Outdoor units require power at all
times to operate their freeze prevention system. In the event of a power outage in freezing weather, you will need to prevent
you tankless from freezing by leaving a faucet dripping or draining the unit until the power comes back on. A “back-up” power
supply or generator is also an option and there have been some solenoid valve products developed that will automatically valve
off and drain down a tankless water heater in the event of a power outage. Performance Another reason that
builders like tankless water heaters is that they are able to provide hot water to todays popular large tubs. A standard
bathtub holds about 35 gallons to the overflow. The popular soaking tubs hold anywhere from 45 gallons to over 80 and just
filling up the tub leaves most without any hot water with a tank type heater for a period of time. A tankless can fill all
the tubs of a home and then provide back to back showers, do the dishes, and wash the clothes. A tank type heater has to
be very large to do all of these things without running out. We are only limited to the flow rate our tankless unit can provide.
Choosing a tankless heater with the proper capacity for our house makes it possible to handle multiple hot water needs at
once without the worry of running out of hot water. Until now, most people made “water rules” to determine who showers when,
or when they could do the clothes or dishes. This goes away with a tankless water heater. Some people mistakenly think that
they will only be able to run one fixture at a time with tankless heater. While this may be true of the “Home Center” models,
this is far from accurate when speaking about the professional grade heaters from Rinnai, Noritz and Takagi. These models
have the capacity to operate 3 showers or more at the same time! Some will correctly claim that tankless water heaters limit
the flow rate to make sure you get the setpoint temperature and say that this means you will not be able to do multiple things
within the home using hot water. This is simply not true. Choosing the right unit is important as discussed a little later,
but making this claim is like comparing all tank water heaters to the old 30-gallon tank heaters that would run out after
every use. Today’s tankless water heaters provide more than enough capacity to meet any hot water need from a one-bathroom
house to a hotel. You just need to choose the correct system for your application just like any other hot water system.
Here is something else to consider when choosing your tankless heater. Asking it to operate three showers, the kitchen sink,
the washing machine, the dishwasher and a laundry sink at the same time is not only unrealistic…your water pipes can’t carry
that much water! Most homes only have a ¾” hot water main and most are now in PEX or CPVC materials. These piping system
can not carry more than about 8 - 10 GPM total, including cold water. Also, many new homes typically see less than 2 GPM
at a showerhead due to pressure looses in the piping. In other words if you choose a tankless heater that can deliver between
6-8GPM in the warm months and 4+ GPM in the winter months you will be quite happy in a typical 3-1/2 bath or less home.
You should avoid the tendency of some to oversize a tankless system based on unrealistic system demands. If in doubt, contact
the manufacture for help. Capacities of these water heaters have improved greatly over the first tankless models that showed
up about 10 years ago in the US. The Largest of these companies (Rinnai) has models that can run from 4.2 GPM to 9.8GPM inculding
residential and commercial units. Noritz has a commercial grade model that can produce up to 13.2 gallons per minute (752
gallons per hour from one unit!) Most of these products can be installed in multi-unit installations for high flow rate demands
like luxury homes, large shower system with body sprays, locker rooms or hotels. (More on this later as well.) Many tankless
water heaters are also installed with a remote control unit that makes it easy to change the set point temperature of the
unit. One manufacturer, Rinnai, has a remote that lets you set an alarm to the capacity of your tub that will actually stop
the flow of water once the tub is filled! You then set the temperature you would like and fill with just the hot water.
When the unit measures the gallons set an alarm sounds to remind you shut off the water and reset the remote and the flow
is stopped. Rinnai, is able to provide multiple remotes to serve the same heater to provide for multiple locations to change
the temperature of the hot water if you like. They even have a wireless remote to allow for easy locating of the remote in
retrofit instalations. These digital remote control panels also provide diagnostics for the water heater in the event that
there is a problem. They flash a fault code to help service personnel find and fix any problems that may come up quickly.
The better tankless heaters by Rinnai, Noritz and Takagi totally control outlet temperature so they can NOT be "overshot"
giving you less than the set point temperature. You always get setpoint temperature plus or minus 1 or 2° (Unlike a tank
which is + or - about 10°) Electric units and home center models do not have this ability. I would advise avoiding the
home center models completely as they lack the technology and BTU’s to give you good performance. In units that can not control
their outlet flow, you will need to “throttle” the flow rate yourself at the outlet. This also means that if you are taking
a shower and someone else turns on another fixture needing hot water, you may get a big surprise as the water temperature
drops considerably in your shower! Serviceability The better tankless heaters are very easy to work on.
(I say the better ones because I have not had to work on a home center unit yet) Like anything else, training is preferred
but any good contractor with a cell phone and a Philips screw driver should be able to take care of a problem using the tech
support lines of the big 3 listed above. A manometer (Device used to measure gas pressure is also a very handy tool to have.
How long do they last? About 20 years on average. Compare that to the 12-year average of tank heaters. This also contributes
to the “total value” of the product since this means lower cost of ownership when factoring in replacement cost and life span
of the product. Add in the long-term energy savings and your tankless heater just might pay for itself and in some cases
it’s replacement! Keep in mind however that installing these units outside in cold climates if there were a power outage,
there is no freeze protection to these units until power is restored. You should protect the unit as detailed above. Most
homeowner’s policies do not cover the water heaters themselves so it is a good idea to provide a generator in these installations
or just put the unit indoors.
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Choosing
The Right Sized Unit
The first thing we need to do is establish the peak hot water demand for the job.
In a home this is usually the number of showerheads, X the flow rate X 80%. Example: 3 showers @ 2.5GPM each = 7.5GPM X 80%
= 6GPM peak demand.
You want to choose a tankless unit that can meet or at least get close to this demand during
the warm half of the year. (Remember it is VERY uncommon to have a demand like this actually happen in a home, plus we are
not going to install a unit that can not control the flow rate anyway.) If you are within 1 GPM of this rate you will be happy.
It is not possible for most people, even plumbers to tell the difference between 1 GPM and 3 GPM without a direct caparison
next to it.
The proper size unit for the home above would be something like the Rinnai R94LSi. The Rinnai website
(www.rinnai.us) even has some great sizing calculators on it as well as an energy cost calculator and even an evironmental impact calculator
to demonstrate how installing their product is good for your wallet and the planet.
Professionals: Please talk
to your local wholesaler about attending a training class on these products. They must be installed properly to work well
and installing them improperly may result in damage to the tankless heater, poor performance, premature failure or injury
to the homeowner.
What about the tank manufacturer’s?
Good question. In the United
States, over 9.5 MILLION tank type water heaters are sold every year! About half of them are electric. That is a huge market.
Every time a tankless company sells a tankless water heater, the tank companies loose a little bit of their market share.
(They don’t sell a tank) It did not take very long for this to get the attention of the big tank companies.
These companies quickly looked into the market. They had some serious questions to ask and decisions to make. The questions
would be along these lines: Is this a fad that will go away? Do these things really do what they say they can do? How long
have these products been in use in other parts of the world and what is their track record? How long will it take us to produce
a market viable unit?
These great companies are full of very smart people. They got their answers and had a group
“Uh-oh” moment. They made a conscious decision that they would not roll over and let the “invaders”
take over their market without a fight.
They found out that over 25 years of research and development went into
these products. With estimates of 5 years before half of the market flipped to tankless, they had to act fast. They knew they
could “Reverse Engineer” the products but that takes a lot of time and they would have to be careful to keep from
violating patents.
The first step by a few of them was to attempt to slow things down. They did this by putting
out letters, and articles touting the “negatives” of tankless heaters. While this was going on on the surface,
they were behind closed doors with the lawyers striking deals with the tankless companies to have units private labeled for
them in an effort to slow down their shrinking market share until they can catch up with the technology.
The results
so far are this: Bradford White has Rinnai manufacturing its “Everhot” tankless water heater line. It IS the Rinnai
line with the BW name on it. State and A. O. Smith had Noritz manufacturing theirs before Noritz severed the relationship.
Then Rinnai made them a generic unit for a short time adn now they BOUGHT Takagi US so all state tankless units are now Takagi.
All that said, the units made by Rinnai and Noritz got very poor product warranty support. AO/State just was not set
up for it and frankly still aren't.
Now don’t think that the very savvy Japanese company’s were
putting the cart before the horse. They know what is going on and they know that they own the technology…for now. They
simply set the whole thing up so their original products still have better pricing on the street and the tank manufacturer
gets "Generic" models. They knew that the tank companies would find someone willing to get the quick sale. By doing
this they at least kept them from partnering with companies making lower quality units. (That could have started a whole new
problem for tankless)
One very large tank company even went to the trouble of taking “their” new tankless
water heater and putting against their tried and true gas fired tank water heaters in a “test”. The parameters
of the test were set up to with high levels of water hardness. They knew that the tankless would require cleaning because
of it and their tanks would not. (Because you can’t!) One thing they did not bother to tell anyone or include in their
“short term” test was that had this test been allowed to continue, the hardness would have certainly ruined the
tanks and required them to be replaced a lot sooner than the tankless which could simply be cleaned. This was done also to
try to slow down the onslaught of tankless while they tried to figure out what to do next.
Most of these tank companies
are still producing papers trying to slow the growth of tankless. (Even the ones with their “private labeled”
products!) They will sometimes make claims using the lower quality of the available units to try to show them as “point
of use” of all them a “Niche product” even eluding to tankless as a fad at times. They will make statements
claiming that they don’t believe in tankless water heaters as “whole house” units. These are just attempts
to “stem the tide” as long as they can unit they can catch up. Some will print more than others but it is all
for the same reason. They need to get people to NOT consider tankless water heaters for as long as they can to protect their
own interests.
So, the big tank companies are worried, as they should be. They are doing what they can, and they
are not going away. Tankless is to water heating what indoor toilets have been to bathrooms!
Warrantees
Tankless water heaters usually have a warranty that covers the heat exchanger and the parts separately. The heat exchanger
is the main part, much like the tank in a tank water hater. Normally the warranty is for about 10-12 years on the heat exchanger
and 3-5 years on the rest of the parts. This average warranty also reflects on the average life expectancy of tankless heaters.
(20 years!) The best warranty of all the tankless manufacturers is Rinnai. They have a 12 year warranty on the heat exchanger
and 5 years on all the rest of the parts and now even a 5-year LABOR warranty! A brief word about warranties.
Manufacturers (Of all Products) tend to set warranties at about half of the life expectancy. Your cars, your dishwasher, your
water heater, all have a warranty that is about one half of the average life expectancy of that product.
The nice
thing is that with a tankless, even if the main part (the heat exchanger) fails after warranty, you have the choice. Replace
the heat exchanger or replace the whole unit. You do not have this luxury if your tank fails in a tank water heater.
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Advanced
Venting Tankless Water Heaters
Venting is very important to gas fired tankless water
heaters. If these products are not vented properly, many bad things can happen. The least of these is the unit may fail very
soon in its life span due to condensate being allowed to enter the product. At the very worse, Carbon Monoxide Poisoning
could occur. “Shortcuts” should never be taken in regards to the venting system on this or any other
piece of equipment that burns gas, oil, wood or other products. All manufacturers’ instructions should be followed and
you should always make sure that your heater is vented properly.
Tankless water heaters can have their venting
go either out a side wall with horizontal venting or up through the roof. Keeping the venting run as short as possible is
both good for the heater and will help keep costs down. In fact, many times it makes sense to move the location of the heater
closer to an outside wall and run the water lines to it rather than run longer venting. (Copper, PEX and CPVC are relatively
cheap compared to Stainless Steel vent piping!) This also may give you a reason to get some needed space back within the home.
Most tankless water heaters require a special vent piping material. This material is known as “Category
III” and is typically AL29-4C Stainless steel but sometimes may be other materials. This is required because the combustion
efficiency of the heaters make it very likely that condensate will be formed within the venting system. This condensate, although
there is not a lot of it, is highly acidic and will destroy standard vent material in a short time. Type “B” gas
vent can not be used on most of these heaters for this reason. Another reason this vent is required is that the vent systems
are under pressure from the fan within the heater. This is known as “Positive Pressure” venting and requires that
the vent system be UL listed as positive pressure and sealed to prevent carbon monoxide from leaking out into the occupied
space. Tankless water heaters as well as other products also have maximum lengths that you can run the venting. The number
of elbows required in the system shortens these distances. Always consult your manufacturer instructions and never exceed
these distances!
It is also not allowed to tie these vents together or tie them into an existing masonry chimney.
The condensing gasses would quickly begin to cause damage to the masonry and result in structural damage to the property as
well as a very unsafe condition with carbon monoxide. If you can run the proper vent product up through an existing chimney
to the outlet and provide the proper condensate drain to protect the unit, you can use the existing chimney as a “chase”
to run your new vent pipe in. (Consult individual manufacturer’s instructions!)
Most manufacturers require
that you either slope horizontal venting away from the heater, or provide some type of condensate drain within 3’ of
the vent connection to protect the unit from damage caused by condensate. The condensate in the venting will destroy the heat
exchanger if allowed to run back to the unit. Units not vented properly will have their heat exchangers ruined within a few
short years. Most vent manufacturer’s now have the ability to provide a drain tee even when venting is installed straight
up to properly protect the unit.
Venting is probably the most important part of a tankless heater installation.
To recap this part: No “B” vent! No Common Venting! No connecting to masonry chimney’s without lining it
with the proper vent pipe. Use Stainless steel UL listed positive pressure venting made for these products. Allow for proper
removal of condensate within the vent system. Keep venting runs to a minimum length. Never exceed manufacturer’s venting
lengths. Read and obey your owner’s manual! ***Even
though some manufacturers allow PVC to be used to vent their tankless water heaters, I personally recomend against it!
A Tankless water heater is subjest to lime scale over time and this can and will reduce the combustion efficiency of the burner.
When this happens, the exhaust emperatures go up and PVC melts at 157*F! This is a very unsafe condition and can result
in injury or death! I do not recomend using tankless water heaters that vent with PVC until such time as their is a
safe way to ensure that PVC is protected from high temperatures. Even Rinnai condensing tankless use a high temperature
Polypropelyne vent instead of PVC for this reason.
Gas Piping
Tankless water heaters
save energy because they are always off and they modulate their firing rate to the demand. However just because they save
energy does not mean your existing gas line is large enough. When these products have to go to high fire to meet a large demand
you must be able to provide enough gas for the unit to function properly. Do not assume that if your existing gas line is
the same size as the connection to your tankless heater that your pipe is large enough. In an existing home it probably is
not!
Most homes with tank water heaters do not have a gas line sized properly for a tankless water heater, especially
if other equipment is connected to the gas piping system. The best solution for this is to run a separate gas line to the
tankless from the meter without re-running the entire gas main. There are many good flexible gas piping systems that can make
this job simple and limit the number of joints and installation time of the new gas line.
Needless to say, gas
piping is not something the average DIY’er should be attempting. The money saved on running a gas line is not worth
the risk of your home and family. Gas piping should always be checked or installed by a licensed and insured contractor trained
for gas piping.
Water Pipe Connections
Tankless water heaters do not come with relief
valves like tank water heaters. Most of the world does not require them on tankless systems. These relief valves should be
installed on the hot water piping leaving the tankless heater. An easy way to do this is to use a tankless water heater valve
set like the Tankless Kit by JOMAR Valves. This valve set gives you only 5 joints to assemble. It has union connections at
the heater, which will greatly speed up replacement later. It has FULL SIZE HANDLE ball isolation valves on each side, drain
valves that give you the ability to flush the tankless system later or drain the unit easily without draining the whole house
and it comes with the proper relief valve. Also, if you are using apipe enclusure or wall box, this kit will allow the Releve
valve to fit inside the box and still be able to operate the valves, unlike other kits. All of this is in a very compact kit
and makes hooking up the water side of your heater fast and easy. This one pipe kit saves about 16 joints at the heater! Make
sure you get the one with the relief valve sized for your heater.
Minimum Flow Rates
A very important consideration when deciding on your tankless water heaters is minimum flow rate. All tankless heaters need
a minimum flow rate and pressure to work properly. You should look for a model that has a minimum flow rate of .5 GPM for
a residential application and one that will operate well down to about 30 PSI system pressure. Some new, higher efficiency condensing
models have a turn on rate of .4GPM! UPDATE! Rinnai models now turn on at.4GPM and will run down as low as .26GPM!
Seisco electric tankless have a turn on rate of .25GPM. This eliminates low flow issues especially on LEED type and
low flow projects.
Even with a minimum flow rate of .5 GPM it is possible to have a flow related problem but it
is a lot easier to solve. If you have single handle bathroom (lavatory) faucets you are going to need to open them all the
way to get the minimum flow rate to fire the heater, especially in the summer time. This is why I advise to not use tankless
water heaters with high minimum flow rates in homes. Commercial units can have minimum flow rates of .75GPM . That is higher
than a minimum flow rate as you would want in a home. Large luxury homes with “carwash” shower systems
do not have very low flow fixtures and typically do not need to worry about minimum flow rates.
Also, Debris in
faucet aerators and showerheads can cut their flow rates down to a point that will keep the tankless from firing. Make sure
your fixtures are free from debris.
Most 2.5 GPM showerheads will not supply 2.5GPM of flow in a new home. This
is due to system pressure looses. Every foot of pipe and each fitting in the water main has a pressure loss. At far ends of
the home these add up and can cause lower flow rates at fixtures like showerheads. This is not a big problem though and rarely
causes issues with the better tankless water heaters. Most people never know the difference and as stated above, it is almost
impossible for most people, even plumbers to tell the difference between 1.5GPM and 2.5 GPM in today’s showerheads without
measuring the flow. As long as the velocity of the water is acceptable most people are quite happy and of course some showerheads
are better than others.
Most tankless water heaters have an inlet water filter. This should be checked and cleaned
regularly to make sure that flow is not slowed or stopped by this filter. This is the first place to look whenever there is
a problem with your tankless water heater. Look for it in your owner’s manual.
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Hard
or Acidic water
Water quality issues can be a concern for tankless water heaters in some areas. To understand
the concern you first need to understand how certain water conditions effect tank and tankless water heaters.
Hard
water is water with large amounts of dissolved solids in it. If you have hard water and pour it into a clean glass, you can
not see the hardness. The hardness is “in suspension” in the water and as the water is heated the particles cling
together and drop out of suspension. In a tank water heater they sink to the bottom and form a layer of scale where they build
up. In a tankless most of the particles are flushed from the system as they drop out of suspension.
Since a tank
heater heats water when you are not using it to maintain the stored water, they tend to get that sediment on the bottom of
the tank. This is because the particles are dropping out of suspension when there is no movement of water in the tank. Even
when you are using hot water with a tank heater there is very little movement of the water. As the sediment builds on the
bottom of most gas fired tank water heater it becomes an insulator and causes the steel to be over heated without a good transfer
of the heat to the water on the other side of the sediment. Over time, the fire burns through the tank or the welds fail and
the tank begins to leak. If the leak is not spotted, then the tank will eventually rupture flooding the house!
In
a tankless water heater, the particles are being flushed from the system as they drop out of suspension due to the high flow
rate through the coils. Some hardness may adhere to the walls of the tubing but it will be a lot slower process than with
a tank. If the water is so hard that the tankless coil becomes fouled the heater will send an “Overheat” or “Lime”
error code (Usually represented with a number) and lock out alerting the homeowner that something is wrong. Rinnai has a special
"LC" error code to alert the home owner before damage is done to the unit. A technician can then come out, diagnose
the problem (With help from the heater error codes) and de-scale the unit, renewing it in about 45 minutes.
Scaling
of gas tankless water heaters is a fairly rare thing. When it happens the water is typically so hard that the homeowner should
consider a water softener system. Water that is that hard is effecting every other appliance in the home. Toilet fill valves,
faucets, washing machines, dishwashers, ice makers, etc. In fact if the water quality is that poor, a softener system will
pay for itself by making these other things last longer and require less maintenance and less frequent replacement, including
the tankless water heater!
Acidic water is another problem. Most water is not going to have this kind of issue,
especially if you are on a public supply. However, if you know you have acidic water, you need to consider installing a neutralizing
system to protect your tankless water heater. Any acidic water that will eat copper piping will eat the copper piping in a
tankless water heater as well and shorten it’s life as well as possibly voiding the warrantee.
If you do
not know if you have hard water or acidic water, chances are you don’t and should worry about it. If you want to be
sure, there are many testing services available for free from companies that sell the treatment systems or you can contact
your local water company or extension agency for testing.
Even if a tankless heater does develop a leak in the
heat exchanger, that part can be replaced and your tankless is back in service without a replacement. With a tank heater,
once the tank gets a leak, you throw it away and get another one. This also makes tankless heaters more environmentally friendly
because less material is going into landfills. Think about the millions of tank water heaters going into landfills every year!
What if water heaters lasted twice as long and were repairable? How much landfill space could we save?
“Cold
water Sandwiches” (Not just for breakfast anymore)
The “Cold water sandwich” is a phenomenon
that can effect a tankless water heater home that is less likely to effect a home with a tank heater. It happens in homes
with tank heaters but can be less noticeable. This is where a section of piping has hot water that has cooled off between
uses and between the piping in the walls or water heater. Piping in the walls looses its heat slower than piping in a crawl
space or basement. If there is a hot water draw and then the flow is stopped for while, the water in the most exposed piping
cools off faster than the water in the piping in the walls. If someone opens a fixture at the right time, the first water
out of the tap is hot, then goes cooler as the water from below gets to the outlet, then heats up again as water from the
heater gets to the fixture. In some homes a tankless water heater can exaggerate this a bit.
Imagine the large
house with a tankless heater and a short draw. One person turns on a faucet at one end of the home and gets hot water to wash
their hands. A few minutes later another person goes into another area and washes their hands. The water in the pipes is still
hot. They are almost done when the temperature goes cold for a few seconds then back to hot again. Viola’ one cold water
sandwich at it’s best.
It does not happen every time and it does not seem to be a regular issue except in
the case of homes with recirculating hot water systems where this has not been accounted for. We will get into that later.
Here is why it happens: When the flow stops a tankless heater stops firing and the draft fan continues to run as a
“post purge” to ensure that all exhaust is moved out of the venting system. It runs for about one minute and during
this time it cools off the heat exchanger. The heat exchanger holds about .2 gallons of water. (a little less that a quart)
When the heater senses flow again it fires back to provide hot water for the next draw. The water in the piping may still
be hot, but the very first bit of water to leave the heat exchanger is not heated. It does take about 1 - 2 seconds for the
tankless heater to get going. Now this first quart of water enters the pipe with the water that is still hot from the last
draw and begins to mix with it as it travels down the line. Eventually the lower temperature water gets to the user and they
notice the temperature fluctuation.
Is this normal? Yes. Is it acceptable? Maybe. In most homes this is perfectly
acceptable since it is not a common occurrence and the short draws are usually hand washing and when this does happen it is
only a minor issue. However if you have just paid for a recirculating system for your home and every time the pump comes on
you get a little slug of cooler water in the piping, it might not be acceptable. When you jump into the shower at the far
end of the home expecting instant hot water and get the surprise from the cold water sandwich, you probably will want to know
how to deal with it. If you are an installer of tankless heaters, then you will want to read and understand the next part
well to provide a perfect hot water system every time.
Recirculating systems (To loop or not to
loop that is the question)
Recirculating systems can work great with tankless water heaters when properly designed
and installed. The proper system will provide instant hot water at most if not all outlets in the home and save the customer
water by not having to run the hot water until hot water gets to the outlet.
The traditional way is to install
a recirculation system is to install pump and a return loop back to the inlet side of the heater with a couple of flow check
valves. This will work of course but you have to install pump with enough “head” capacity to get through the high
head loss of the tankless. Higher head pumps also use more electricity to operate than their lower head counterparts. How
big a deal is that? Well if a higher head pump uses $.02 more to operate per kWh then the other pump, over a 20-year operating
period that calculates into the thousands of dollars over the life of the pump!
Another consideration is most
tankless water heaters get their energy efficiency and their longevity by being “always off”. Installing a recirculating
system this way puts a lot more wear on the unit and may cut it’s warranty in many cases. Add the cold water sandwich
to the equation and there is a better way.
One of the first things that installers dealt with was the cold water
sandwich. This was managed by installing a very small storage tank (About 5 gallons) right after the tankless heater. This
way, if a small slug of hot water got out of the tankless it would mix with the 5 gallons of hot water in the tank and be
diluted to a point where no temperature change would be noticed. That fixes the cold water sandwich but still leaves the high
head pump and the warranty issue to deal with.
At some point someone came up with the idea of turning that small
storage tank into a 5 or 6 gallon 110V tank water heater. They are very small, insulated, and can plug into an outlet. Then
they hooked up the recirc loop between the tankless heater and the small tank heater effectively by-passing the tankless,
saving the warranty and keeping the energy efficiency of the unit. The small tank heater does not have to heat the water very
much. When the system is first turned on, a hot water fixture is opened filling the entire system with hot water including
the small tank. The tank and recirculating system now only has to use enough energy to maintain the loop temperature. This
is usually only about a 5° rise. With insulation on the hot water piping, it is a very efficient solution! Instant hot
water, as efficient as you can be with very low energy demands, and all the hot water you will ever need.
If you
would like a diagram of this system, contact Rinnai through www.rinnai.us. They will be able to provide this to you or your contractor. The
best circulating system by far for any tankless water heater is the ACT Metlund D' Mand system. It is also "on
Demand" and "always off". With this system you get total control, it only cost about $1 / yr to operate
adn does not void any warranties! see www.gothotwater.com for details.
Twin tankless systems
There are many reasons to go to a “Twin”
tankless system. You may have a big house with 4 or more baths and a large family, or you may have a large flow capacity shower
system installed and need a higher flow rate. A good gas tankless water heater can easily operate 3 showers in the winter
months, and even 4 in the summer months due to warmer incoming water temperatures. If you need more that that you may want
to consider a twin system.
When you install a twin system you should always choose a tankless water heater that
is made to operate this way. If you were to just choose two tankless heaters and pipe them together you would compound their
minimum flow rates. If you have two tankless heaters with a .5GPM minimum flow rate and piped them in parallel without installing
them properly, you will end up with a 1GPM minimum flow rate before either heater will fire! Plus you would have a very unbalanced
flow through each heater. If you hooked them up in series, you would never be able to get a higher flow rate than the full
capacity of one heater.
Rinnai, Noritz and Takagi all have units that are made for multi-unit and twin system installation.
Hooked up in a twin system, when there is a low demand one unit will work by itself with the other automatically
valves and turned off. When the demand increases to about 50% of the capacity of the first unit, the second unit is brought
online and load is balanced between them. The heaters will work together up to their peak capacity. They also will act as
a “lead/Lag” system in that the “lead” unit will change after every few operating hours so it does
not get more wear than the other one. Another great benefit of this system is that if one unit develops a problem, the system
will lock it out and valve it off, sending an error code to the remote. The other heater will operate normally up to its capacity.
This is called “Redundancy” and it means you are never out of hot water, even if there is a problem.
Wiring these system is not difficult and the instructions do a very good job in guiding the installer to hooking up the
system for the first time.
There are very few homes that need more hot water than a twin tankless system can produce.
With the average heater from Rinnai, Noritz or Takagi, you will get from .5GPM – 16GPM depending on incoming water temperature.
That’s from the lowest flow rate required for hand washing up to 960 gallons per hour of hot water! All that and you
still have not taken up any floor space of the home, and have no tanks to burst.
The question comes up often “Should
I just put one at each end of the house and let them be separate?” You can of course do this if you like. It is two
separate hot water systems and you do not get the redundancy of the true twin system however you may eliminate the need for
a recirculating system in a larger home. The choice is up to you and you should simply consider what benefits are most important
to you and how your home will be used. If it is just a lot of bathrooms like a 5 or 6 bath home, but you do not have any high
flow fixtures, it may make more sense to just place them at opposite ends and have two hot water tankless systems. This is
very likely to cost less money up front then a twin system with a recirculating system in a large home.
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Multi-unit
tankless systems
The multi-unit tankless systems work much like the twin systems above. The systems from
Rinnai, Noritz and Takagi all use a multi-unit control that acts as a lead/lag system. You get a lot of redundancy with a
system like this.
These are usually commercial applications with very high demands like locker rooms, dormitories,
hotels or industrial applications. Every once in a while a large luxury home is built that has a high flow demand that requires
such a system.
With the Rinnai system you have one multi-unit control that handles up to 6 of their heaters. If
you need more than that, you can use more than one multi-unit control.
Noritz and Takagi have a similar controls.
The Rinnai control also balances out the run time on each heater in the system to ensure that all units work the same amount
of time over their life.
The wiring harness’ are included in with all these systems and are not difficult
for the professional installer although proper training is highly recommended. All three of these companies have very good
technical support teams to help any contractor who needs or would like a little reassurance on their first big job.
Look at this example: A high school has a locker room with 24 showers. They have a 10 year old 400 gallon tank water heaters
that is “always on” 24/7/365 and it has begun to leak needing replacement probably due to sediment build up caused
by constantly heating and reheating water that is not moving. A typical locker room has to have a hot water system sized that
will meet the peak demand, however the kids almost NEVER use it! At best, the showers get used a few dozen times a year after
a football or other game. The rest of the year, the big old tank is just sitting there wasting valuable energy.
For
this job* I would recommend 5 Rinnai C-98 units (Indoor or outdoor models) and the MSA-2M control with 3 MSA 2S wiring harness'
(*This is for my area and meant only as an example! Your area may require more or less capacity.)
This system would
be “always off” but with plenty of capacity to supply the team with hot water when they needed it. With today’s
high gas prices the savings would be well into the thousands of dollars per year and the heaters would probably last past
their 20-year life expectance due to light use. An installation like this usually pays for itself in the first 2-5 years after
installation in energy savings and is a much better use of taxpayer money.
One other thing to consider for this
installation is replacement cost. If you have a tankless heater that ends up needing replacement, you have a small piece of
equipment to replace. A heater like the one in the above example lists for between $4,000 and $4500. A large commercial tank
heater for this job would run more like $10,000. The labor involved in replacing large tank heaters is also much higher. These
large tanks weigh 500-700 pounds or more requiring heavy rigging and special equipment along with people who know how to handle
such large items. Tankless heaters like the one in the example weigh about 80-100 lbs. and can be handled by two men without
special equipment. This represents a dramatic savings in the overall cost of ownership over the life of a system.
Combo systems: providing both domestic hot water and hydronic heating with a tankless heater
To
put it simply, YES YOU CAN! As many people already know, there are great advantages in supplying heat with hot water in a
home along with a domestic hot water source. This has been done for years beginning with boilers using tankless coils or indirect
hot water heaters and also with tank water heaters doing both heat and domestic hot water. The tank water heaters went through
a phase a few years ago where tens (If not hundreds) of thousands of heaters were installed in this manner with good success.
Among the advantages is the fact that one piece of equipment lowers costs of installation and saves space. You also
get the warmth and comfort of hydronic heat. Air moving over a hydronic heating coil tends to be warmer than hot air produced
by a heat pump especially when it is really cold outside and the heat pump is running at lower efficiencies.
Tankless
water heaters have plenty of BTU capacity for most homes, however some care must be taken in the design of the system to ensure
that adequate flow capacity will remain to supply the hot water needs of the residence.
One thing to keep in mind
also is that 1GPM of flow equals 10,000BTUs of heating capacity. This means that even though you may have a 199,000 BTU tankless
water heater, if your maximum flow rate is 8GPM at a 20° rise, you are limited to 80,000BTUs of usable energy to heat
the house. (Still plenty for most average sized homes) This is the way most heating systems are designed. There is a way to
get more BTU out of a tankless heating system that will be discussed later by altering the design.
The tankless
market knows that there is a huge opportunity for tankless to take over this type of job and we can expect many great developments
over the next few years to help this equipment do an even better job than it can now. For now, we can take some steps to ensure
that the current tankless heaters do a fine job in a home of meeting this need and saving energy. At the same time we will
understand the limits of these systems to determine at what point another system would make more sense either by system needs
or an overall cost/comfort benefit.
Since we are limited in the flow capacity of a tankless water heater and for
sake of this discussion, we are going to assume that we are using a tankless heater capable of 6GPM+ at a 45° rise and
is capable of about 8GPM at a 20° rise.
If we were to use this heater for both heat and hot water in an average
2 – 3 bath home without any special considerations we would probably have a problem based on flow. The typical hydronic
coil requires between 3-4GPM of flow to provide heat. For instance, if the hydronic circulator is running and delivering 4GPM
of flow to the heating system and there is a need to operate a shower at the same time, we are going to be at or very near
the capacity of the tankless heater. If we wanted to be able to provide hot water for two or more showers at the same time
that the heat was running we would have very poor water pressure at the shower heads at best. Two or more showerheads would
be trying to split about 3GPM of flow capacity. In a smaller 1 bath home or condo of course this is not a problem, but for
homes where there are 2 or more bathrooms there is a solution that provides the best of both worlds.
This system
needs to be installed with “Domestic Water Priority”. What this means is we are going to ensure that if there
is a domestic hot water need, we will always give that priority over the heating system on a temporary basis. This has been
done for years in homes with boilers to make sure that the boiler could do both of these jobs without having to oversize it.
We are going to “borrow” this technology to use it with tankless water heaters.
The best way to give
a tankless water heater domestic priority is to install a flow switch (like the McDonnel Miller FS4-3T-3) in the cold water
supply piping to the tankless heater. This switch is wired to break the white thermostat wire on flow. (The “call for
heat” wire) This switch takes about 1 GPM to operate. In fact, by pulling your domestic hot water line off of the heating
loop, you will get hot water faster to remote areas in the winter when the heating system is operational. (You're pulling
off of a pipe that is already full of hot water, closer to the fixture.) Of course if you use a model with a matching Air
Handler, priority will come built in.
Here is how it works: During a heating load the circulator is running
and the system is acting as a “closed loop”. In other words, no flow is coming through the cold water inlet piping
where the flow switch is located. If there is a small hot water flow demand such as a sink, there is only a small likelihood
that the heating system would effected since it takes at least 1GPM top operate the flow switch. However if a domestic water
demand like a shower, requiring 2GPM of hot water happens, the flow switch will sense the flow coming through the cold water
inlet piping and temporarily turn off the heating system during that load. Once the load is finished, the heating system will
begin operating as usual.
This type of system leaves you with full capacity for both heating and domestic hot water
using a tankless heater. You most likely would never even notice the temporary deactivation of the heating system any more
than you notice it now when the heat turns off.
Using a tankless heater as a boiler
Many
times the question is asked “Can I use a tankless water heater as a boiler?” This may be as a replacement to a
boiler system or as a cost saving method during new construction. Many times only a small BTU load is required such as smaller
radiant floor heating systems. In these cases a tankless water heater may offer cost benefits over a conventional boiler.
After all, a tankless water heater is very similar to a small wall mounted copper-finned boiler! NEW INFORMATION!
THe Federal Government will not allow tankless water heater manufacturers to sell their equipment as boilers unles they have
a "boiler stamp" on them. For this reason Tankless manufacturers can not and do not recomend them anylonger
as boilers. Using them as a boiler will almost always void the warranty. This is one area where the electric tankless
companies like Seisco have a tremendous advantage! They make a small electric hydronic unit with sizes from just over
17,000BTUH to 95,000 BTUH! This can be a great alternative for small radiant zones.
Use a Modulating Condensing (Mod/Con) boiler if you can Typical boilers are
either on or off at their full input. A Mod/Con heating a space under a reduced load will operate at a lower firing rate and
save fuel. The energy savings alone will be greater than the life cycle costs of a unit, including it’s eventual
replacement. Plus, boiler and hydronic technology is advancing at great speeds. 10 years from now there will be even better
options for small modulating high efficiency equipment at pricing lower than is currently available.
Another consideration
is the piping method. Primary/secondary is the preferred method of piping a tankless water heater to a large hydronic system
and many Mod/Con boilers come with the header piping for this. This enables the primary loop pump to maintain a good flow
through the boiler and allows the boiler to modulate according to the temperature rise demand of the system, even when only
one or two small zones are operating. Sometimes if only a small zone is operating, the Mod/Con may cycle off until the water
temperature in the primary loop cools enough to require it to operate. However, in single loop baseboard projects a standard
loop with a properly sized pump will work fine. Many, like the Rinnai even come with "outdoor reset" which
allows the boiler to change it's output temperature based on how cold it is outside! This makes it even more efficient
and your home even more comfortable. If you have a small radiant or hydronic heating zone, consider
an electric hydronic unit such as the ones from Seisco. They can offer very good performance with a substantially lower up
front cost. (More in my blog and in the electric tankless section of this article below)
Squeezing more
BTUs out of a tankless heating system
Because Mod/Con boilers are not limited to high return water temperatures
like conventional boilers, they can introduce added flexibility in heating system design by allowing for use of a higher Delta
T (the difference in the supply and return water temperatures). As a result, a Mod/Con can provide more BTU capacity per gallons
per minute (GPM flow).
This concept is important to understand when there is a need for more than the typical 10,000
BTU per GPM to heat a space. For example, increasing the design Delta T from the standard of 20º to 25º delivers
an increased output of 2,500 BTU per GPM flow.
At 1 GPM with a 20º rise, 10,000BTU is delivered. If we change
the 20º delta-T to 25º, the delivery rate for 1GPM is 12,500. At a 30º Rise it is 15,000BTU per GPM of flow!
As a result this enables the installer to get more usable BTUs from a smaller capacity system when there is only a modest
increase needed. For instance, a home needs 87,000BTUs of heat under design day conditions. If the heat loss was determined
using the standard 20º delta T, many standard residential boilers would not have enough capacity and a larger, more expensive
unit would be needed. By changing the design to a 25º delta T, an extra 2,500BTU per GPM of flow from that same boiler
can be obtained. If the boiler is capable of 8GPM it can now have a heating capacity of 100,000BTU (12,500BTU per GPM X 8).
Although price is certainly not everything, this tankless water heater system has a very large advantage over the price of
a 100,000BTU boiler.
This is something many professionals do not know or have not considered. By replacing a standard
boiler with a modern modulating condensing boiler, you will not get the advantage of the high efficiency unless you alter
the design of the buildings heating system! In other words, if you install a mod-con in a system designed to operate at a
20ºdelta-T, once the system is operating up to the set point temperature, your boiler will not condense and you loose
some of the advantage of higher combustion efficiency! The system needs to be set up with a higher temperature differential
to maintain the advantage of condensing equipment. Of course you still get the advantage of the modulating capacity.
Another thing to cosider if you have an old style Cast Iron boiler that also provides domestic hot water is that
getting rid of the old iron boiler and replaceing it with a Mod/Con will save you on AIR CONDITIONING too! How?
Simple, Your boiler has to run during the warm months 24/7 to keep all that iron hot and keep the domestic hot water coil
ready to provide hot water. This is adding a lot off heat to the house when you are trying to cool it with A/C. By
going to a combination Mod/Con unit, your boiler is "Always off" like a tankless water heater and you are
not heating the house with a big chunk of hot cast iron. This will greatly effect your energy bill on cooling! Trouble shooting tankless heatersTankless water heaters have very little trouble.
When they do have an issue, it is usually right after installation and something easily corrected that has to do with the
installation. Anything else that happens later will require professional attention and would be beyond the scope of this article.
However here are a few common things to look out for. One important thing to remember. If you have a hot water problem and
there is no error code on the remote, there is nothing wrong with the heater! That does not mean you don’t have a problem,
it just means that something else is going on. It will be something minor and easy to fix once you find it. First
step Clean the filter! It sounds simple and it is. This is going to be answer to 90% or more of the problems that show up
later. It does not require tools and is a homeowner job. Although all the major manufacturers recommend doing this monthly
we all know you won't. You will only think about it when you have a hot water issue and if you are on a good clean source
of water you may never have to clean it. If your installer offers a preventative maintenance program, I encourage
you to sign up for it. This is a good way to keep your tankless running at it’s best and will lengthen it’s life
as well as keep you from having nuisance problems that always seem to occur on Friday afternoon of a holiday weekend, right
before your guests are going to arrive! Alternating water temperatures. There are three causes for this. The first
is the cold water sandwich effect we already discussed. The second is a crossed water line. If you are having this issue in
a new home you may notice that you get good hot water near the unit but much cooler water in remote areas. To identify or
rule out a crossed water line you simply shut the cold water valve to the tankless and open the hot water (only) faucet in
the house. Pressure should quickly bleed off to nothing. If water keeps flowing, you have proved a crossed water line. (Now
you just have to figure out where it is.) Homeowners, this is not a big deal! When you are working on a big house on your
back, crawling and climbing and changing sides of walls it is very easy to cross a water line. Every plumber has or will have
this happen at some point in their career. It will be easy for them to correct and everything will be fine. The
third cause is lack of flow. Picture a 2.5GPM showerhead in a home. Many times they only give you about 1gpm of flow in a
new home due to pressure losses or debris in the flow restrictor. If the incoming water is high (Like in summer month is warmer
climates) you need very little hot water at the shower valve to make your shower. It is easy to fall below the required flow
rate to keep the heater running. It looks like this: the person gets in the shower and turns it on to full hot to get the
water there. They then set the temperature to a comfortable level and gets in. They don’t know that the heater just
shut off because of low flow and the pipes are now full of hot water. A few minutes later the temperature in the shower drops
and they adjust to use more hot water. The heater fires back up and a few minutes later it’s too hot, so they turn it
back down and the whole thing starts over! The solution: Clean the filter, clean the showerhead, and if both were already
clean, remove the flow restrictor from the head. (LAST RESORT ONLY!) Those first two are more for the homeowner.
For you pros doing your first few tankless there are some other things that might catch you. Here is a quick summary of what
I have seen: Too small a gas line (Very common!), wrong fuel type, forgot to turn on the gas valve, no combustion air, improper
venting, water lines hooked up backwards, vent graded back to the heater with no condensate drain, blocked vent, wrong sized
pump in HVAC application, improper recirc systems (See above) and improper vent termination. (Such as terminating the vent
too close to the ground in an area subject to snow) I even heard of one job where an outdoor unit was installed in the interior
hallway of a dentist office! YIKES! Unfortunately, I don’t have enough webspace to go into all of these
little issues. All of them have great stories to go with them and some of them are quite humorous, but the moral of this is
to help you realize that even though you may have been in plumbing for 30 years, you will have to go through the learning
curve of tankless. It’s not bad, it’s just a little different with different things to trip you up than you are
used to. With the great tech support of the big 3, you will be up to speed in no time. Go to every training you can, and do
as many of the installs as you can. It won’t take long for you for you to be a big supporter of these products if you
give them a chance. Just make time for the trainings and stay away from models that do not have good support including good
local reps! You need to know these people and the good ones will quickly earn your trust and your business. Homeowners,
any time you see an error code flashing on your remote, you want to contact the installer or the manufacturer right away!
It may be as simple as a #12 code, and you let your propane tank run out of gas, or may be an LC code and the unit requires
service and a de-scale. Either way, that’s the time to have things checked out. LC codes or overheat codes require attention
right away. It’s not a danger to you, but it is to your unit. If Limescale is a known problem consider one of
the electronic descale devices like HydroCare. www.hydrocareusa.comElectric tankless water heatersThere are several good electric tankless models out
there and they are cheaper to operate than their tank counterparts. The problem comes with people who are so eager to get
a sale that they overstate or downright lie about their performance or operating efficiency! I hope to help
clear that up here. First let’s look at efficiency. An electric tank water heater operates at about 99% operating
efficiency! With a gas unit, even tankless, we are about 82 – 85% efficient. Wow! So electric’s are more efficient
than gas right? Wrong! All that means is that out of every $1 of electricity you spend, you get $.99 worth of heat into the
water. With gas if you are 85% efficient, the other $.15 of heat goes out the vent. What they don’t tell you is that
it takes a lot more electricity dollars to make hot water than it does gas dollars (Or even oil for that matter!) in every
case. Of course now we have high efficiency tankless gas water heaters also that operate at over 90% so you have even more
options. In every case we have the yellow Energyguide sticker to help us out. This is an “estimate”
of the cost to operate the product for a year. With water heaters it is based on a typical family of 4 with a 2000 gallon/month
hot water use. This gives the consumer a level playing field to judge energy use that is not supplied to them by someone selling
them something. Anyone who tries to discount the validity of this information is either ignorant of the facts or at worse,
a liar and should in either case be avoided. Here is one of my favorites: Electric water heaters have 0 emissions.
Gas ones produce greenhouse gasses. Really? And just what made all of that great electricity, hmmmm? No need to spell all
this out is there? Performance: Electric tankless heaters need to have a large electrical service to operate well
in all but the very warmest of climates. A quick glance at their temperature rise charts will tell you that if you expect
to operate more than one fixture at a time in most of the upper two thirds of the US you will need about a 100 amp unit at
a minimum and in most cases a 120 amp unit. If you only require operating one fixture at a time you may be ok with an 80 amp
unit. In any case most homes (not all by any means!) will need an electrical upgrade to have an electric tankless installed.
With this added cost, it is going to be more attractive to place a propane tank in the yard and use that for your hot water
needs. It will cost less up front, have much better performance and cost less to operate (See the Energyguide stickers!)
An exception to this rule is Seisco. They have a patented energy management system that allows the unit to come on at
10% of it's load and ramp up from there, much like a gas tankless. This means that instead of a 120amp unit slamming
on at full power, dimming your lights and then powering down, theirs comes on smoothly, and powers up to the needed load.
This means that the appliance is rated differently electrically, and by electric code, and in most cases even the 120 amp
unit may be installed in a normal 200 amp panel as long as there is space for the breaker. (The Panel load on the RA32 is
only 54 Amps!) in a home where gas is not an option, this would be a good choice as long as one considers and understands
the capability of the unit. For instance, a RA32 in central Virginia can be expected to handle 2.5 baths. In Florida
you could probably do 3.5 - 4 baths. The same unit in Michigan, might only be good for 1.5 bath home. Contact
your local Rep for help if you need it. The other problem with performance they have is that they do not control
their water flow, which means they CAN’T control the outgoing water temperature if you overshoot their capacity. For
instance, a 120amp unit will give you about 3gpm of hot water at a 50º rise. You are the person in a shower when
some else in the house opens a tub spout to fill the tub and the flow rate total now goes to about 6 gpm. Guess what happens
to your shower temperature? You are going to get a big surprise! Homeowners do not generally have a problem with a slight
reduction in velocity from a shower head but they very much have a problem with a shower going instantly to cold! As
long as you understand this when deciding on an electric tankless water heater, you should be happy. Just be sure you
know what you are getting and choose a good quality unit and more importantly make sure it's installed correctly! Electric
tankless with the wrong sized wires or breakers can be a big problem.
I believe that electric
tankless water heaters have their place. A small remote suite may be one. An apartment or condo where you can't have
a vent or gas for some reason or as “under-the-sink” point of use units. Possibly even a remote
cabin where there is no propane available (Also rare) They also can be very handy for a small radiant heat zone where a gas
tankless is simply way oversized. This is perhaps the best and most overlooked place for them!
So far the biggest
electric tankless out there to my knowledge is a 120amp unit and this will give you about 4.5GPM @ a 45º rise. This is
ok for up to two fixtures of use in most cases. Maybe one more in warmer months or “down south”, and maybe less
up north. The two best models in my opinion are Seisco or Stieble Eltron.
If you are looking to boost
capacity of your tank , you might also look at the Seisco Supercharger. It is a 7KW or 9KW unit that installs right
after your tank and can over double the capacity while not greatly impacting your energy use or take up the room of a
second tank. It's job is to simply raise the water temperture when the tank begins running out of hot water. This
is a great way to increase capacity without a large upfront cost. These units only run about $360 plus installation
and can take your 2 shower tank to a 4 shower or more appliance! Drain Pans
Drain Pans are required by every major plumbing code and most building codes for “water heaters” when
installed where a leak could cause damage to the structure. In a word, anywhere you would need a pan for a tank, you should
have one for the tankless. It’s true that they do not have a tank to burst, but everything eventually reaches the end
of its lifecycle. All major tankless brands also call for installing a suitable drain pan anytime a unit is installed
in an area where a leak can cause water damage. (Look in their installation instructions!)There is at least one
on the market currently and is available at major plumbing wholesalers. The website is www.thewallsaver.com Since Code also states that any equipment must be installed per manufacturer's instructions, if your tankless is going
in a closet, attic, condo or other place where it will cause damage when it eventually dies, you should also be installing
a pan. It will save many tens of thousands of dollars in water damage eventually. There you have it. Now
stop wasting space and energy with a tank heater designed 100 years ago. Have a quality tankless water heater professionally
installed. They are good for your wallet, great for the planet, and an investment that gives you unlimited hot water every
time you need it! Be sure to see all the great calculators at the Rinnai website. www.rinnai.us. Plus get valuable coupons towards your unit and find a local trained installer. I hope you found this article
helpfull. Please feel free to contact me if have any other questions.
M. Scott Gregg (also the author of Profitable Plumbing)
is a Rinnai trainer, a former Nortiz trainer and a licensed Master Plumber in the state of Virginia.
© Copyright
2006, M. Scott Gregg
All rights reserved.
No part of this work may be reproduced, stored in a retrieval system,
or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from
the author.
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UPDATES Updates have been made to the folloowing sections: "electric tankless water heater" , "using
tankless as a boiler", "Low Flow Rates" A short electric tankless artice has been added to my blog on
the blog page.
NEW tankless Video Series HERE
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