Do I Need an Expansion Tank in My DHW System?

I have a natural gas water heater that every week or so often, discharges water from the pressure relief valve (valve located on top of the tank that a long drip pipe is connected to, this goes to the floor). I come down to the basement and see there is water on the floor; not alot, maybe a gallon or less. One opinion I've received is that there is too much pressure in the tank which causes the relief valve to operate and that I need an expansion tank to better handle the pressure changes.

In all the houses I've lived in, I don't ever recall seeing an expansion tank on the hot water side of things, only on the boiler side of the piping for baseboard heating. Actually I think the fault is with the water heater. What do you guys think is the issue? Thanks...

no you don't need an expansion tank. you need a new pressure relief valve. If you replace that and it still misbehaves you probably need a new heater( bad aquastat)

Do you have a well or city water? If you have a well or a backflow preventer on your system its a closed system and you need an expansion tank. For a 40 gallon an ST5 would be sufficient.

plumber wrote:Do you have a well or city water? If you have a well or a backflow preventer on your system its a closed system and you need an expansion tank. For a 40 gallon an ST5 would be sufficient.

City water. I'll look for a backflow preventer.

If your relief was truly bad it wouldn't leak intermittently, it would leak all the time. Should be replaced though, after they pop, they only get weaker. Any type of check valve on your water service makes your house a closed system. Water expands when heated and needs to go somewhere.

I pretty sure there is no backflow preventer in the system. I followed the line where it enters the home and up to the water heater. The incoming line does a "loop" on itself and feeds into a water meter but I'm pretty sure there is no backflow preventer integrated into this.

NJJoe wrote:

plumber wrote:Do you have a well or city water? If you have a well or a backflow preventer on your system its a closed system and you need an expansion tank. For a 40 gallon an ST5 would be sufficient.

City water. I'll look for a backflow preventer.

What is your water pressure coming into the house. In my old house ( City water) I had to install a regulator because the pressure was to high.

I have no idea what the incoming pressure is. Pressure seems good; we can take showers and wash dishes without feeling like the pressure is starved.

NJJoe wrote:I have no idea what the incoming pressure is. Pressure seems good; we can take showers and wash dishes without feeling like the pressure is starved.

I was wondering if it is too high or has surges that go higher.