Expansion Tank w Water Pressure Regulator?

When installing a Water Pressure Regulator, how important is it to also install a Water Expansion Tank?

Thanks so much,
Steve

It's very imporant! Without the PRV, when the WH runs, the expanding water can actually push back out into the street supply. Water doesn't compress, so that extra volume needs somewhere to go. The PRV has an internal check valve, so now the whole house system is referred to as closed. Now, when you run hot water and replace it with (denser) cold, when it is heated, it expands and must go somewhere. It will go out the weakest link...could be a weak hose splits on a faucet supply, drip out a marginal faucet, damage the hose to the washing machine, or if all those are in good shape, dump water out of the T&P valve on the WH until the pressure is relieved. This isn't normally very much, but will happen any time you run a large enough amount of hot water, close the (say shower) valve, and then that replaced water gets heated.

Add one. It needs to go between the shutoff supply to the WH and the WH cold inlet.

Generally it is true an expansion tank is required with a PRV got for the reasons cited. It is my understanding that there are some PRV's that have a bypass built in, but otherwise you definitely need the expansion tank. They are pretty inexpensive, in the $50 to $60 range. They come in a couple of sizes, and should be sized to your home.

IF the PRV has a bypass, the house pressure has to exceed the supply pressure to open it. Depending on where you live, that may still cause other problems. And, code requires one when you have a check valve. Basically, many towns are now trying to make their supply safer...letting your house push water back into their system can pollute the water for everyone downstream from your supply. So, many are installing check valves at the meter (and might not tell you), creating a problem for the homeowner with the T&P valve releasing to relieve the pressure.

Thanks alot gentleman.

steveg91 said:

When installing a Water Pressure Regulator, how important is it to also install a Water Expansion Tank?

Thanks so much,
Steve

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Hmm I wouldn't say it's necessary but it's a good idea. If you're going to put one in install it on the hot side of your hot water tank. This is the best spot for it.

jadnashua said:

IF the PRV has a bypass, the house pressure has to exceed the supply pressure to open it. Depending on where you live, that may still cause other problems. And, code requires one when you have a check valve. Basically, many towns are now trying to make their supply safer...letting your house push water back into their system can pollute the water for everyone downstream from your supply. So, many are installing check valves at the meter (and might not tell you), creating a problem for the homeowner with the T&P valve releasing to relieve the pressure.

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Hmm sort of. Most PRV I install aren't internally loaded with a check valve per say. They are naturally open and the water down stream (your domestic water) is what actually closes the valve. So if your house pressure is lets say 100 psi do to thermal expansion it should technically just want to close your PRV tighter. Not force its' way around it.

Doherty Plumbing said:

Hmm I wouldn't say it's necessary but it's a good idea. If you're going to put one in install it on the hot side of your hot water tank. This is the best spot for it.
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You are a plumber? A Licensed plumber? One with some experience under his belt?

I pray you are not a plumber in the state of Illinois. Here is the part in the Illinois plumbing code about how and where to install the expansion tank.

SewerRatz said:

You are a plumber? A Licensed plumber? One with some experience under his belt?

I pray you are not a plumber in the state of Illinois. Here is the part in the Illinois plumbing code about how and where to install the expansion tank.

A properly sized and approved expansion tank shall be located on the outlet side of the check valve, PRV or backflow preventer, in the water heater's cold water supply with no shut-off valve between the heater and expansion tank.​

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Up here in BC we aren't required to put them in. So the only mistake I made was you guys are forced to put them in on the cold water inlet of your tanks. We put them on the hot water outlet. Same effect.

Also if you read that code clause it doesn't say you have to put the expansion tank at the PRV etc. It just says you have to one one the outlet side between it and the tank with no shut off valves in between. You could put it on the inlet of the HWT it self with a couple of brass fittings.

Doherty Plumbing said:

Up here in BC we aren't required to put them in. So the only mistake I made was you guys are forced to put them in on the cold water inlet of your tanks. We put them on the hot water outlet. Same effect.

Also if you read that code clause it doesn't say you have to put the expansion tank at the PRV etc. It just says you have to one one the outlet side between it and the tank with no shut off valves in between. You could put it on the inlet of the HWT it self with a couple of brass fittings.

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Since there is not be a shut off valve installed between the expansion tank the the water heater, we normaly do plumb a Tee in at the top of the water heater and install the expansion tank on one side of the tee, then the water supply with shut off on the other.

We do the same thing but on the outlet of the HWT.

Doherty Plumbing said:

We do the same thing but on the outlet of the HWT.

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The manufacturers here say to put it in on the cold side. Failure to do that often risks premature failure.