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Old 01-11-2016, 04:33 PM   #1
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thermal expansion tank


Hi - I'm about to replace my 40gallon water heater. I like to try and do things 'right' so i was reading up on the latest water heater stuff, as it's been 10+ yrs since I last replaced one.

I've started reading about 'thermal expansion tanks'. I think i sort of understand what they do - i'm just not entirely understanding if I need one. It would be a moderately difficult task to install one (limited space), but do-able.

I live in a single family home in West Los Angeles - I've never had any issues with pressure regulation in the past. My water is just piped into the house from the street.

How do i determine if I need to install one or not?

thanks in advance,
Matt
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Old 01-11-2016, 04:46 PM   #2
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If you have a pressure reducing valve (prv) installed on main incoming line or a closed loop system you will need one.

Other than that check with your local municipality and ask them if one is needed in your location. They should know the appropriate code requirements.
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Old 01-11-2016, 05:11 PM   #3
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thanks - I do have a pressure reducing valve, so it sounds like i would need to install a thermal expansion tank.

I actually have two hot water heaters - how do i ensure coverage of both - do i need to install one tank at each heater, or can i install a single larger tank on the cold water pipe prior to where it T's off to the hot water heaters?

Last edited by mmhendrie; 01-11-2016 at 05:18 PM.
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Old 01-11-2016, 05:15 PM   #4
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You only need the PRV if you have very high water pressure. Take the above advice and inquire. No sense spending money on something you don't need . In my case the paltry excuse for the mater main is a 3 1/2 Inc pipe. Last thing I need is to reduce my pressure. (50 psi on a good day
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Old 01-11-2016, 06:39 PM   #5
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Quote:
Originally Posted by mmhendrie View Post
thanks - I do have a pressure reducing valve, so it sounds like i would need to install a thermal expansion tank.

I actually have two hot water heaters - how do i ensure coverage of both - do i need to install one tank at each heater, or can i install a single larger tank on the cold water pipe prior to where it T's off to the hot water heaters?
Check out this link for info on the tanks function and how to size

http://www.watts.com/pages/learnabou...lExpansion.asp
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Old 01-11-2016, 09:42 PM   #6
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How big are both tanks combined? That is the size you can use for the above chart.
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Old 01-19-2016, 03:26 PM   #7
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apologies on the slow response - i've been sick.

So the house is a single story bungalow that is very wide - all the 'wet' rooms are located on each extreme wing of the house - the south wing has a 30gallon WH feeding the kitchen/laundry room/small bathroom, the north wing has a 40gallon WH feeding the two main bathrooms. My assumption is it was designed this way as there would be a substantial wait/water waste in moving cold water out of the pipes till it warmed. The water heaters are probably a little over 100' apart in distance.

Could i select *any* point on the cold water line, after the pressure regulator for the house, and place a single thermal expansion tank rated for 70gallons, and be covered for both WH's?

-Matt
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Old 01-19-2016, 03:38 PM   #8
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you dont need one, the water heater acts like an expansion tank..if you converted to a tankless water heater, then you will need one..or if you are having problems with water hammer..spend your money on a 3/4 inch( whole house) water filter for the cold side of the heater to help keep junk out of the new heater...as you are suppose to flush the bottom of a water heater every 6 to 12 months to clear the sediment off the bottom for better heating and avoiding rusty water..
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Old 01-19-2016, 04:18 PM   #9
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Oh my gawd
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Old 01-19-2016, 04:31 PM   #10
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No, a water heater does not act as an expansion tank. A water heater needs an expansion tank because each new tankful of water expands slightly as it is heated. A pressure tank for a well pump can act as an expansion tank.

One expansion tank of adequate size for the quantity of water in the various water heater tanks, placed anywhere in the plumbing, will work provided that there are no closed valves or check valves between any of the heaters and the expansion tank.

Code inspectors like to see an individual tank above each water heater so it can be easily determined that the expansion tank exists.
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Last edited by AllanJ; 01-19-2016 at 04:44 PM.
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Old 01-19-2016, 05:46 PM   #11
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Just add one for the 70 Gallons total water your heaters hold. The expansion tank has absolutely nothing to do with water hammer.

You need a Watts PLT-12 one that will do 2.3 gallons or better.
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Old 01-19-2016, 07:59 PM   #12
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Quote:
Originally Posted by AllanJ View Post
No, a water heater does not act as an expansion tank. A water heater needs an expansion tank because each new tankful of water expands slightly as it is heated. A pressure tank for a well pump can act as an expansion tank.

One expansion tank of adequate size for the quantity of water in the various water heater tanks, placed anywhere in the plumbing, will work provided that there are no closed valves or check valves between any of the heaters and the expansion tank.

Code inspectors like to see an individual tank above each water heater so it can be easily determined that the expansion tank exists.
sorry water heaters do not need expansion tanks....and the op stated he does not have an expansion tank and has had no issues since hes been there..
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Old 01-19-2016, 08:00 PM   #13
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Quote:
Originally Posted by Ghostmaker View Post
Just add one for the 70 Gallons total water your heaters hold. The expansion tank has absolutely nothing to do with water hammer.

You need a Watts PLT-12 one that will do 2.3 gallons or better.
then what does it have to do with?
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Old 01-19-2016, 08:11 PM   #14
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Quote:
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sorry water heaters do not need expansion tanks....and the op stated he does not have an expansion tank and has had no issues since hes been there..
Since he has a PRV he has a closed system. Previous history aside, I'm betting it is now a code requirement for his jurisdiction
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Old 01-19-2016, 08:12 PM   #15
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Quote:
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then what does it have to do with?
Thermo expansion of water
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