# Thermal expansion tanks - hot or cold side?



## Alan

I was just thinking about this today, and it crosses my mind from time to time, so i thought I'd share, and see what you guys do.

Seems like the other plumbers in the area put the thermal tanks on the hot side. Why? Doesn't excessive amount of heat ruin rubber? Thats what the guts in them things are, aren't they?

I was at a Grundfos seminar about a year ago, and this guy (company rep) was talking about recirc systems and hot water heaters, and somehow-or-another, he got to talking about expansion tanks, and he says "and what side do we put the expansion tank on?" Like zombies everyone else replied "on the hot side". Then he asks : "And why do we do that?" followed by the sound of crickets. He answered his own question with : "because hot water heaters have that little heat trap check valve nipple that won't allow the expanded water to flow back into the cold piping.

Me : :blink::blink::blink::blink:

I was dying to ask the question "So are you telling me that you can fill a hot water heater to pressure through the hot nipple, and nothing will come out the cold side?"

His claim seemed outrageous without even giving it a second thought, and it got me wondering how many people are putting them on the hot side. I've been taught to put on the cold because supposedly it will last longer.

How are you doing it and why? Maybe this has been discussed and I missed it. 

Holla back.


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## smellslike$tome

Cold side, always. In between the wh isolation valve and the inlet to the tank.


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## Tankless

Water heater. Just water heater, not hot water heater :jester:!!

I have never heard of a tank heater with some kind of check valve built into them. I would bet my left one, there is no such thing.

I assume the reason he got into this topic was because a recirc system should / could have a check valve on the return line. An Xpantion is required when the cold is checked or a back flow is installed. Simple enough.

That said I only put them on the cold side. That's the way I was taught and to me, anything else is wrong. There is a temp rating on the bladders that allows up to 170 F I think...I forget. So in theory it is perfectly acceptable to do them on the hot side, but I do them on the cold side.


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## Titan Plumbing

Tankless said:


> Water heater. Just water heater, not hot water heater :jester:!!
> 
> *I have never heard of a tank heater with some kind of check valve built into them. I would bet my left one, there is no such thing.*
> 
> I assume the reason he got into this topic was because a recirc system should / could have a check valve on the return line. An Xpantion is required when the cold is checked or a back flow is installed. Simple enough.
> 
> That said I only put them on the cold side. That's the way I was taught and to me, anything else is wrong. There is a temp rating on the bladders that allows up to 170 F I think...I forget. So in theory it is perfectly acceptable to do them on the hot side, but I do them on the cold side.


Heat trap nipples come to mind...................


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## ChrisConnor

Bradford white used to have these little balls in their nipples. Now they are just little rubber flaps. 

I put mine on the cold side.


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## Tankless

Choctaw said:


> Heat trap nipples come to mind...................


 
I don't consider heat traps in the same ball park as check valves, but I see your point.


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## Alan

Choctaw said:


> Heat trap nipples come to mind...................


:yes: Those little plastic and rubber thingies inside of the cold nipple that I always haul out with a pair of needlenose...

Thats what he was referring to. I can't remember why I know this for certain, but I am 100%.


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## Titan Plumbing

Tankless said:


> I don't consider heat traps in the same ball park as check valves, but I see your point.


Alright then....keep your lefty. :thumbsup:

Oh and BTW....cold side after the ball valve.


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## Tankless

Choctaw said:


> Alright then....keep your lefty. :thumbsup:
> 
> Oh and BTW....cold side after the ball valve.


 
Ya know what, take the damn thing and his buddy. over the years they have only gotten me into trouble and have cost me a lot of money:no:


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## rickmccarthy

I was Taught on the Hot side and that is how I have always done it. The theory I was taught was that it is for thermal expansion and to take that extra pressure off the system also not just the tank.


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## Alan

rickmccarthy said:


> The theory I was taught was that it is for thermal expansion and to take that extra pressure off the system also not just the tank.


If you think about it though, wouldn't it do the same thing on the cold side, and the rubber inside would last longer as it isn't quite as heated? The water expands through the entire system, not just the hot side.


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## Ron

We don't install TET's, but if I had to it would be on the cold side of the tank.


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## gear junkie

Biggest reason to put expansion tanks on the cold side is because that is the guidance from the manufactors.


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## Alan

gear junkie said:


> Biggest reason to put expansion tanks on the cold side is because that is the guidance from the manufactors.


Good point. Actually I meant to mention that in my original post, but it got lost in all the typing.

Ron - LOL @ you signature. WTH did that come from? :blink::laughing:


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## rocksteady

Skyhook is Ron's alter-ego. :laughing:







Paul


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## nhmaster3015

What you do is open up the little piece of paper that comes in the box. It has what the manufacturers call "Directions" printed on it. Usually is English and Spanish also. Every expansion tank I have ever installed had "directions" that said to install it on the cold side. And since inspectors sort of insist on you following "directions" I strongly suggest doing so. :thumbsup:


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## macp&h

http://www.amtrol.com/pdf/9015-087revDTXT.pdf Hope this helps


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## nhmaster3015

Ohhhhhhhh lookie..... Directions, imagine that :thumbup:


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## Alan

This wasn't a how-to post, guys. :furious:


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## Miguel

Here's an ST-12 I did a while ago in a tight location. The pic doesn't show it but there's a valve/checkvalve then the TEE for the TXT.


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## Alan

Miguel said:


> Here's an ST-12 I did a while ago in a tight location. The pic doesn't show it but there's a valve/checkvalve then the TEE for the TXT.


Do the gas rheems have an option for top or side T&P ?

It really irritates me that the electrics don't. They always put them in at funky angles and overtighten the heck out of them. :furious:


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## Plumber Jim

If you pipe it on the hot side you can create a pocket of cooler water. lets say the tank has 2 gallons of water in it from expansion. as it cools it will send that cooler water into the hot line. If it is on the cold line it will fill with cold water and when you open a hot faucet the cold will leave the tank and feed into the cold inlet of the heater. on the hot side it will feed the water in the tank with the hot leaving the water heater which would drop the temperature a little. I know it shouldn't be much to be a big deal but that's what i was told is the reason for putting it on the cold side.


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## retired rooter

When the heaters first changed and started needing exp tanks,I knew a guy who would get [email protected] valves rated at 175lbs ,I saw him cutting the safety tag off the pop off valve to CHA(cover his arsh) it seems the extra 25lbs was enough to keep most from popping off.


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## Bill

Tankless said:


> Water heater. Just water heater, not hot water heater :jester:!!


Sounds like someones feathers are ruffled:laughing:


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## Miguel

Bill said:


> Sounds like someones feathers are ruffled:laughing:


 
LOL! It bugs me too, though. It _HEATS _water, not hot water! 
But if you boil it right down, sequiter intended, most times you *are *heating hot (or lukewarm) water.
We should call them lukewarm water heater tanks. (Even tankless ones... call them lukewarm water heater tanks with no tank.) 

Naw, everyone would just call them lukewarm hot water heaters. :sad:


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## Miguel

Alan said:


> Do the gas rheems have an option for top or side T&P ?
> 
> It really irritates me that the electrics don't. They always put them in at funky angles and overtighten the heck out of them. :furious:


I'm not sure. Not here, anyway. Code sez "direct to the tank within the top 6" of the tank" (actually they changed that to the top 15 cm but you get the idea).
I haven't installed this make for awhile (the pic is a few years old) but almost all of them came with the relief tight but still needing the "snugging" to get the true vertical drop. I didn't come across any that were overtightened but I guess that depends on Pedro or Miguel  might have moved up to quality control (or BW or State) and some other slob is spinning those things in now.


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## Miguel

Plumber Jim said:


> If you pipe it on the hot side you can create a pocket of cooler water. lets say the tank has 2 gallons of water in it from expansion. as it cools it will send that cooler water into the hot line. If it is on the cold line it will fill with cold water and when you open a hot faucet the cold will leave the tank and feed into the cold inlet of the heater. on the hot side it will feed the water in the tank with the hot leaving the water heater which would drop the temperature a little. I know it shouldn't be much to be a big deal but that's what i was told is the reason for putting it on the cold side.


Shouldn't be a big deal at all if the pressure's fairly constant, which it only is after a PRV and the street side doesn't diminish too much, but it's another good point. Never thought of that angle.

Edit: AND the tank pressure is set properly! :whistling2:

Look at me with 3 replies in a row! Wot a post-count pig! Sry!


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## ranman

i was taught to always to read the install install standards and fallow them.
a product became approved because of them, not how i think it should be installed
if it fails and it was not installed per the standard you are responsible.


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## rickmccarthy

DUR AX SHUNS what dem is


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