Water Heaters and Expansion Tanks

[Nick Ostrowski]

I see some new water heater installations with expansion tanks installed and some without. Is there any requirement to have an expansion tank with water heaters?

[Wayne Carlisle]

Anytime you have a closed system then you must install a expansion tank.

A closed system could be caused by a check valve in line that does not allow the water to expand while being heated. The water has to expand somewhere so you install a expansion tank to allow for thermal expansion. Without a expansion tank there could be enough pressure that would cause pipes to start leaking, faucets that leak etc.

Make sense????

[Nick Ostrowski]

Yes, makes sense. But installations have not always been like that. When were expansion tanks required?

[Wayne Carlisle]

I believe....... I don't know :) I'm not where I can research your question... Hopefully someone else will chime in!

[Vern Heiler]

Yes, makes sense. But installations have not always been like that. When were expansion tanks required?

I'm not sure what code cycle, but to me as a HI it doesn't really matter if it is a closed system. Just remember, it doesn't have to be a "tank" there are other expansion "devices" and they don't have to be near the water heater.

[Bob Harper]

The EPA has been requiring backflow prevention for years but it is rarely enforced. A backflow preventer requires an expansion tank.

In areas with high water pressure, a pressure regulator must be installed with the backflow preventer so it, too would require a tank.

If you live in defiance of the EPA regs. and have less than 85psi water supply, then a tank is not required. As for the plumbing code requiring BF prevention, it is confusing enough that most AHJs don't require it except at specific hazards such as boiler feeds, fire sprinklers and lawn irrigation systems. See IRC P2902 for crystal clear details...

[Jerry Peck]

The expansion tank is not required.

Control of thermal expansion pressure is what is required.

Control of thermal expansion can be done with the installation of a pressure relief valve ... as much as I dislike pressure relief valves and their installation - they are allowed.