A few months back I moved my laundry room from a cramped closet to a different area of my house. There was not a hot water line running to this room but there is an exterior outside faucet on the wall we relocated our washing machine to. The plumber tapped into that outside exterior wall faucet and installed a new water heater off of that line. This water heater only services the laundry room's washing machine. Over the holidays I noticed that the cold side line of the water heater was warm (actually rather hot) to the touch. I texted my plumber to see if i needed a check valve or something, and his reply was:
"It's called thermo expansion and you only need it if you had a closed system and your system is not closed."

This doesn't make any sense to me. I can't see how this is efficient or normal. Is this really nothing to worry about? Or, is my plumber incorrect? When I shutoff the water to the house using my inside shutoff (pre-water filter), that outside faucet also is off. Hence, the exterior faucet is part of my house copper lines and not on it's own system.

This message has been edited. Last edited by: Xfratboy,

Nipples are available that have plastic check valves installed that tend to help hold the "hot" where it belongs. [In the tank]. 3/4" in diameter,about 2" long, one for the cold, one for the hot, they are threaded into the unit before you would do the rest of the hock up.
Might they be missing? This could be the problem. If so a trip to your local hardware store, a pipe wrench and teflon paste is a rather strait forward fix. {I'm old school, I would rather use paste than tape.} But that is just me.
And yes you are heating standing water so you do have an energy & money waste present.

I installed a set of those in the folks' house when I replumbed it to copper. hot water flow was restricted, and a couple years later, I pulled 'em out. brown with what I assume was organic material.

the pipes didn't grow any of that stuff.

it's a catch-22, those check valves. yeah, they isolate hot from cold. but that is considered a backup safety device as hot water expands slightly.

I'm not doing them again.

Wouldn't you need to install an expansion tank if you put a check valve on the water line? A water heater will push the expanding water back towards the meter as the water heats. It isn't much, but it does need a place to go.

its not hurting a thing. worry only if you start getting hot water coming out of a fixture
sence you are not useing the fixture often, the water in tank is heating up and expanding. it wont hurt a thing
if it does get to bothering you have your plumber install an expansion tank
or a expansion loop in the piping system

My town will be adding check valves at the water meters, when they do we need to have an expansion tank installed. Not sure where you think the water is going to expand to while heating. The only place it has to go is out the TPV if a check valve prevents it from going back out the cold water line towards the main.

When I replaced my water heater a few years ago I added an expansion tank.

I too have scene houses in these parts that have expansion tanks tied into the water heater. But only a few, compared to all the oil or coal boilers. Certainly would make sense, expansion wise.

yes it does. but you can do it cheaper
by using an expansion loop
run a straight line of pipe, north to south, make a 90 degree offset east 12 inch
then a 90 degree offset north. 5 ft
90 degree west 12 inch
then reconnect to the north/south straight line
simple, expansion loop
we use it to expand steam lines and hot water heating lines

quote:

Originally posted by CommonwealthSparky:
I too have scene houses in these parts that have expansion tanks tied into the water heater. But only a few, compared to all the oil or coal boilers. Certainly would make sense, expansion wise.

They only started requiring them when the looked to add check valves to protect the public water supply from possible contaminants getting pulled into the system in case of a water main break. If for example you had a hose end yard chemical sprayer attached to a hose in the event of a break the vacuum could pull this into the public water supply. It is my understanding that is why the toilet fill valves have the little hose that dumps water down the overflow while filling. If there was a break the pressure would suck air and not tank water.

Anyway, the tanks run less the $40. I'm not a plumber but I think Frodo's solution is to compensate for the expansion of the pipes as they get heated by the water. They do the same thing on oil pipelines to compensate for the expansion from the hot oil.