Water Heater Temp

[jadnashua]

Water expands when you heat it. It has to go somewhere. Often, it just pushes back out into the supply mains, back into the street. That means that if you polute that supply, you could be polluting everyone else connected to that supply. This could come from having a garden hose sitting in a puddle and there's a hiccup in the supply pressure, a handheld shower sitting in the tub without a working vacuum breaker, or other problems. Some cities put in a check valve to prevent that. Some places need a pressure reduction valve to bring the supply pressure back down to reasonable levels. Each of those create a 'closed' system...water can come in, but can't go back out. So, when that hot water expands, it could break something, leak past worn seals, or drip out the T&P valve protecting the WH. To prevent issues when the city periodically replaces water meters, or does other service, some places madate that an expansion tank be installed. This gives that water someplace to go without stressing all of the fixtures, pipes, and hoses in the house and often discharges from the T&P valve. So...it's not a bad idea to have one, regardless.

[GabeS]

So there can be no harm in installing an expansion tank at all?

How come in NYC, I barely see them on water heaters? Even on new installs I don't see them?

[SewerRatz]

Gabes: You defiantly need an expansion tank installed if there is any kind of backflow device IE a checkvalve on the cold water supply, an RPZ or duel check valve at the meter.

[GabeS]

Got it. I justed wanted to say got it, but it wouldn't let me, said my message was too short. Must be at least 10 characters.

[Scuba_Dave]

I haven't seen expansion tanks anywhere around here on WH around here either. I see them on boilers every time - pretty sure

[jadnashua]

Almost all boilers are closed systems, and require the use of an expansion tank. Same is true of any potable water system that ends up being closed.

[GabeS]

Almost all boilers are closed systems, and require the use of an expansion tank. Same is true of any potable water system that ends up being closed.

Aren't all potable water systems closed systems?? But not all have expansion tanks. In fact I barely see them here in NYC on no water heaters.

[jadnashua]

No, potable water systems in many places are totally open in the sense that water from the house can flow back out into the mains. Only when you throw in a check vavle does it become closed. A PRV has one, the utility may install one either in their water meter or as part of the installation either now or in the future. They do tend to replace the meters, and newer ones often come with a check valve, thus, some municipalities require an expansion tank to be installed so there isn't a rash of service calls when their T&P valves start leaking.


T&P Valve looking at two sides.

[kingsotall]

Got it. I justed wanted to say got it, but it wouldn't let me, said my message was too short. Must be at least 10 characters.

I hate that.