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Old 02-09-2010, 10:00 PM   #1
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Default Thermal expansion tanks - hot or cold side?

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 :

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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Old 02-09-2010, 10:43 PM   #2
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Cold side, always. In between the wh isolation valve and the inlet to the tank.
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Old 02-09-2010, 10:47 PM   #3
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Water heater. Just water heater, not hot water heater !!

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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Old 02-09-2010, 10:50 PM   #4
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Quote:
Originally Posted by Tankless View Post
Water heater. Just water heater, not hot water heater !!

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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Old 02-09-2010, 10:55 PM   #5
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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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Old 02-09-2010, 10:55 PM   #6
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Quote:
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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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Old 02-09-2010, 10:59 PM   #7
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Quote:
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Heat trap nipples come to mind...................
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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Old 02-09-2010, 10:59 PM   #8
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Quote:
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I don't consider heat traps in the same ball park as check valves, but I see your point.
Alright then....keep your lefty.

Oh and BTW....cold side after the ball valve.
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Old 02-09-2010, 11:08 PM   #9
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Quote:
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Alright then....keep your lefty.

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
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Old 02-09-2010, 11:15 PM   #10
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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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