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Old 10-23-2008, 11:53 AM   #1
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Default Water Heater Expansion Tank

We rarely if ever install an expansion tanks on water heater installations in our area. When installed, we've seen them installed on the hot side because that's the side that experiences expansion. However, we've seen them on the cold side, and the instructions of some manufacturers specify it on the cold side. The problem with that is that if the water heater has an internal check valve (ball) on the cold inlet, it won't do much good.

Our Michigan Plumbing Code does not specify.

What say you?

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Old 10-23-2008, 12:08 PM   #2
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Water is at a static state when not in use, those heat traps are not moving unless the water is running, expansion will have no effect on the heat traps. So this will allow water to expand within system in all direction. If code does no specify how installation is to be done them manufacturer instructions apply.
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Old 10-23-2008, 03:44 PM   #3
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Water is also hydrolic, and can not be compressed. Since hot water will take up more space than cold, This water WILL go some where, the expansion can happen on your tank causing premature tank failure, or if you have an old water meter with out a check valve the water may actually push back down the line causing the meter to spin backwards. With reclaimed water systems being installed all over down here, they (the city) are installing meters with double check valves, they will then require a means of thermal expansion in the system. This may be done with 2 devices that I am familiar with. 1- Expansion tank- see manufactureer recomendations for appropriate size to heater and installation locations ( usually the inlet side between the heater and the water service but be sure there arent any other check valves in the sysem ie circ line etc. and then the blow off device, usually installed on a tee at the first hose bibb above the water service or homes main shut off. If there is not a check valve on the meter then the inspectors here will allow the meter as a meens of thermal expansion. We have some great inspectors here, who use there heads!! I know you don't hear that very often.
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Old 10-23-2008, 05:06 PM   #4
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I don't really care for em. But some guys use a governor 80 toilet fill valve to control pressure spike from thermal expansion.

HO usually wonders why the toilet is running and has it changed to a standard 400a or something. Put expansion back at square one.
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Old 10-23-2008, 05:38 PM   #5
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We don't install hardly any expansion tanks, last one I did was about 4 years ago. I don't see many out there around here.
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Old 10-23-2008, 07:47 PM   #6
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Whenever we "close" a system (install a pressure reducing valve) we provide means for thermal expansion. Asupertech is right on about static pressures of water. A check valve will only work is differential perssures exist. That's why they're never seen on heating systems. Once the pressure equalizes(circulator turns off) the check valve gate will float around since there is no pressure differential to keep is closed.

The code used to be that whenever a water distribution was closed and there eas a water heater tank volume greater than 50 gallons, then you had to provide means of thermal expansion. Now I believe that if you close a system period, you need to provide mw=eans for thermal expansion. That's the 2003 International Residential Code though, it may be different elsewhere.
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Old 10-23-2008, 07:52 PM   #7
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A few cities here in AZ require them. We had a few of them develop holes around the center of the tank. Caused several thousand dollars damage to walls, wood floors, etc. Manufacturer was pretty good about it though.
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Old 10-23-2008, 08:05 PM   #8
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EVERY water heater gets one on city water. The local water department is steadily putting checkvalves on the meters, so they are required by code. People with check-valves on the meter sometimes get drippy relief valves until we install a TXT.
I always install them on the cold side, but I don't think it makes much difference either way.
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Old 10-23-2008, 09:33 PM   #9
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The IPC requires an expansion tank and there is no exception for prv's meter's or the lack there of.

We install them on every install, new or replacement.
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Old 10-23-2008, 09:36 PM   #10
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Here? Only on commercial jobs.
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