I was just reading an article about the "importance" of a thermalexpansion tank to extend the lifetime of water heaters, T&P releasevalves, hot water fixtures, etc.On the other hand, we have never had one in our house or where I grewup and I haven't "noticed" any problems.Specifically, we have a 40 gallon gas-fired water heater on city waterwith 3/4" inlet and outlet to the water heater and copper plumbingthroughout the house. We have 4 bathrooms and a kitchen. The citywater pressure comes in at about 85 PSI.How important is it to add a thermal expansion tank or is this one ofthose "if it ain't broke, don't fix it" kind of things?Alternatively, is there enough "give" either forward through the hotwater plumbing or backward through the cold water plumbing (andultimately maybe even back into the city mains) to allow sufficientroom for expansion?If a thermal expansion tank is recommended, any suggestions on brands,models and sizes?

My understanding & experience is that an expansion tank is only neededwhen your house is isolated from city supply by some sort of backflowprevention device.With such a device installed, cold water coming into your system toreplace hot water consumed & being heated by the water heater cangenerate enough pressure to pop your water heater T&P valve.The only signifant "give" in your systems is back flow into the citymain. If you have a back flow prevention device then you need arelief valve (set higher than citty pressure plus hammer spikes &lower than water heater Y&P valve) or an expansion tank.If oyu have an open system (backk flow into main) forget the expansiontank....not gonna do much.cheersBob

Thermal Expansion tank for water heater

Thermal Expansion tank for water heater - is it necessary?

Jul 20, 2009 24 Replies

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tony 9 years ago

replying to blueman, tony wrote: I do not see any benefits on the hot water heater. However if that was heater for house that would be different story. No expansion thank for water heater is unnecessary it will do nothing for you, 40 gallon water heater is little small for that size of house.

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trader_4 9 years ago

A vertical pipe filled with air isn't going to stay filled with air for long. The air winds up dissolving into the water under pressure. That's why water storage tanks on pumps need either a mechanism to inject air as needed or a plastic bladder to separate the air and water.

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trader_4 9 years ago

He just said that without an expansion tank, the pressure goes up to 100 PSI and the TPR valve starts leaking.

However if that was heater

See above.

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AL 9 years ago

When I moved into my house there was an expansion tank. When I had the hot water heater replaced recently the guy removed the expansion tank. When I questioned this he said the new water heater was designed to not need one. He was apparently right since the pressure does remain constant throughout the cycle.

BTW I'm late to the thread so please excuse if already covered.

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gregz 9 years ago

Took me a while to figure that out. I installed one since my pressure relief valve kept popping. Thats too many pounds. Don't like the projected life of only 6 years.

Greg

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