# Thermal  Expansion  On  Water  Heaters



## globe trekker (Aug 6, 2010)

I have a "new" residence that will be installing two separate water heaters in the attic.

The plumber-of-record wants to know if thermal expansion tanks / devices are

required on each water heater,  or just on one of them.

*QUESTION:*  Are thermal expansion devices on just one water heater capable enough

to allow for thermal expansion on the whole potable water system,  or is each water

heater "required" to have thermal expansion capabilities installed?

We are on the `06 I-codes.   Thanks for your input!  

.


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## Builder Bob (Aug 6, 2010)

Are the water heaters in series or parallel? any check valves between them? Not enough info to make an answer however, manufactures specs usually provide information for the "recommended" size of the thermal expansion tank to be installed based upon water heater size. There is where you may find the most correct answer.


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## Uncle Bob (Aug 6, 2010)

DO NOT INSTALL RESIDENTIAL HOT WATER HEATERS IN SERIES!

It voids the warranty.

Here is A. O. Smiths piping diagram for hot water heaters "IN PARALLEL";

http://www.hotwater.com/lit/wiring/315268-000.pdf

The thermal expansion tank is installed on the water line that feeds both water heaters.

Hope this helps,

Uncle Bob


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## Builder Bob (Aug 6, 2010)

UB, I know about water heaters in series..... Just baiting the hook so to speak to see what would nibble......   gotta start noodleing and leave the fishing pole at home.


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## globe trekker (Aug 6, 2010)

I am not absolutely sure as to how the water heaters will be installed, ...whether or not

they will be installed "in series" or "in parallel." The plumber said that they would be

installing two separate water heaters, ...in two separate areas of the residence attic

and were two expansion valves "REQUIRED" or could they just install only the one

for the both of the water heaters. My first response to him was " ...install two

separate expansion valves". If I am wrong / incorrect in this interpretation,

then I will gladly go to him and correct it. I just need to know what is the

correct ruling from the codes.

The plumber called me back today and said that he HAD contacted the

manufacturer; or their representative, of the two planned water heater installs,

and that the manufacturer had said that the expansion valves on their water

heaters were designed to accomodate the thermal expansion on the whole

system, ...meaning - - on more than one single water heater. I have not

received anything in writing from the plumber or the manufacturer for review.

Not sure of the WH manufacturer...

So, I am seeking ya'lls "most valuable" input! What say ye?  

.


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## mtlogcabin (Aug 6, 2010)

Expansion control would only be required if you have a check valve, backflow preventer or a pressure reducing valve installed in the system. Check out TABLE M2003.2 it gives some sizing requirements for boilers



> [the manufacturer had said that the expansion valves on their water heaters were designed to accomodate the thermal expansion on the whole system, .../QUOTE]You can't use a relief valve ( that is what he is calling an expansion valve) to control thermal expansion
> 
> P2601.1 Scope.
> 
> ...


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## globe trekker (Aug 6, 2010)

mtlogcabin,

My mistake!   

My question should have been to address "thermal expansion" for both of the

two separate WH, and NOT thermal expansion valves.

.


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## RJJ (Aug 6, 2010)

It needs to be sized for the two units combined. What size HW? And What size expansion tank?


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## globe trekker (Aug 6, 2010)

RJJ,

I do not know what size of WH's are proposed.    I will have to obtain that information and

post it on here.   Also, the manufacturer of the WH's.

The plumber DID mention something about sizing / capability of the system [ in gallons ]

to allow for the expansion of each WH.

.

.


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## Uncle Bob (Aug 6, 2010)

Globe,

see page 3; Sizing Expansion tanks;

http://www.americanwaterheater.com/support/manuals/0002911480.pdf

Note: Expansion tanks are not to be installed in areas subject to freezing.


The expansion tank, piping, and your connections may in time leak. Select a location

where a water leak will not damage the surrounding area. The manufacturer is not
​responsible for any water damage in connection with this expansion tank.



Two good reasons for not putting expansion tanks in attics.



Hope this helps,

Uncle Bob


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## globe trekker (Aug 6, 2010)

Uncle Bob,

Thanks for the link.    Does that sizing chart,  or would the manufacturer' sizing

chart apply to each WH installed,  or would one expansion tank be adequate

for all WH's installed?      In my case,  two WH's " XX " gallons?

Essentially, I am seeing / hearing that our AHJ will need to refer to the

manufacturer' installation instructions;  as Builder Bob initially stated, to

see if an expansion tank is "required"  on each WH.

Ya'll are simply "THE BEST!"      I wholeheartedly agree with ewenme,

...this is one reason why this forum works so well.

.


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## Uncle Bob (Aug 6, 2010)

Globe,

I add some stuff to my last post that might be helpful.

The expansion device just needs to be somewhere ; on the cold water side (that is not prohibited by the manufacturer) in the potable water system.

For example WATTS makes one for toilet tanks; which I don't prefer.

Here is some good information from WATTS;

http://www.watts.com/pages/learnAbout/thermalExpansion.asp?catId=64

Uncle Bob


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## RJJ (Aug 6, 2010)

If they must be in the attic and it is not condition space they can in stall the expansion tank in the cold water feed in a condition area.


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## peach (Aug 7, 2010)

why would you put a water heater in an area subject to freezing in the first place? (since I don't know where Globe trekker is from).


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## Uncle Bob (Aug 7, 2010)

Peach,

Over the last 10 years; central and south Texas haven't had winters with several consecutive days below freezing (enough to cause a freeze problem in attics).

Unfortunately, most major builders have used this temporary weather situation; to run water lines in attics without insulating them; and have placed their water heaters and HVAC units in the attic. More square footage with less cost.

This is a disaster just waiting to happen; and no one will pay except the homeowner.

I have other horror stories about water heaters in attics; but, not on track with this subject.

Ya'll don't forget the leak warning from the expansion tank manufacturers; they will leak; and the leak is not covered by the manufacturer. Just like the water heater; where any leak may cause damage to the structure; you will have to provide a pan below the expansion tank; with pan drain line to an approved location.

ps. Most people go straight to Chapter 28, Water Heaters in the IRC. Don't overlook Chapter 20 Boilers and Water Heaters, Section M2003 and Table 2003.2 for additional requirements for expansion tanks.

Uncle Bob


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## peach (Aug 7, 2010)

I don't know where the OP is from.. but I can say that we didn't install them in attics in Florida, either.. (freezing was not a big issue in Central FL.. so they were in the garages)..

I'll be visiting a home in DC in the next week to look at the "approved" installation .. which I believe includes uninsulated water lines in the attic (we do have freezing days here).


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## RJJ (Aug 7, 2010)

Not a good idea, but as long as they meet code it is ok. If it is outside the conditioned space they need insulation. We are running sprinkler lines for 13d systems in attics. Oh they have insulation or freeze protection.

In office and strip stores a lot of WH are above the ceiling. It is all about space. SF is of value!


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## peach (Aug 8, 2010)

RJJ... that building we went to look at is putting a dry system in the attic for the top floor; they failed their wet system hydro on Friday... of course, it's a 13R, not D system and it'll still be in insulated space.

In offices and strip stores here, the WH are usually elevated in the very small mechanical rooms, not above the ceiling.


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## RJJ (Aug 8, 2010)

I have problems with the 13d or r if they are wet in unconditioned space. I know I have to except them! Every Time we have a cold snap and the wind chill is down around 2 or 3 degrees I have at least one freeze up and later a water flow. Which brings out the fire guys.


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## skipharper (Aug 9, 2010)

The question is about thermal expansion and water heaters but I see a sprinkler system got into the threads, aint read them all but the thermal expansion tank, based on the initial questions is:

607.3.1 Pressure-reducing valve.

For water service system sizes up to and including 2 inches (51 mm), a device for controlling pressure shall be installed where, because of thermal expansion, the pressure on the downstream side of a pressure-reducing valve exceeds the pressure-reducing valve setting.

607.3.2 Backflow prevention device or check valve.

Where a backflow prevention device, check valve or other device is installed on a water supply system utilizing storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.

In other words, if you have a water service with a backflow preventer at the meter or in the building, a well water service with a check valve, or check valves at the water heater(s)then yes, a closed system has been created and the tank is now required anywhere on the water distribution system


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## peach (Aug 9, 2010)

I guess I wonder.. even if you put insulating blankets on the water heater, how much heat still escapes into the attic?  (I guess if you get snow, you'll know).


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## RJJ (Aug 10, 2010)

Yes Skip! We did drift into freezing conditions in attics for 13R systems. It is peaches fault she is the one who hijacked the thread. Thanks for bringing us back to center.


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## north star (Aug 10, 2010)

** * **

*Yes peach, ...stay on topic! * 

*FWIW, I too have seen the water heaters in the attic spaces.*

*It IS a **space saving design, so the 'misses ' can have more*

*room for **stuff and ' froo-froo '. It just doesn't appeal*

*to the **females too much to have them down stairs.*

** * **


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