Residential water heater for floor relief valve

lucky131969

My Mom has a radiant floor heat system in the basement. It uses a 40 gallon water heater. It has been working well for years, but the water heater started to leak, and was replaced by a local plumber. All the air was evacuated from the system, and it is working normally......but....I noticed the water heater has a 150 psi relief valve. Given the application, should this be changed to a 30 psi valve?

Thanks in advance,

Mike

rick in Alaska

No. The relief valve is rated for the unit it is hooked to, which in this case is a water heater, not a boiler. The water heater will take much more pressure than the boiler will. However, I am not sure on the component side of the radiant system how that is rated. I have never had a reason to check the pressure rating of say, manifolds , pressure tanks, and such. That would dictate the pressure relief valve size.
I would think putting a 30 psi relief on the piping would protect the heating side of things, but you would still want to have the water heater thermostat installed as it has the over temperature addition that will protect the tank.
Rick

hot_rod

What pressure is the system running? Does it have an expansion tank?

EBEBRATT-Ed

I agree with @rick in Alaska add a 30psi relief valve on the piping. Leave the one on the water heater which is a T & P.

I don't think you can buy a low pressure T & P. Even if you could it might require a larger than a 3/4 tapping

hot_rod

water heater relief valves are both pressure and temperature, I would not remove one. Leave it in and also in the proper location.
Adding a second 30 psi, pressure only is a good idea for dedicated hydronic use.

Knowing that most water heaters are not listed for closed loop hydronic heating.

lucky131969

hot rod said:

What pressure is the system running? Does it have an expansion tank?

Pressure is about 12-13 psi on the gauge. Yes, it does have an expansion tank. Verified pre-charge at 12 psi.

hot_rod

There may be some components in the hydronic loop that are not 150 psi rated, so those are not protected by the 150 psi relief valve. Regular hydronic expansion tanks are usually 100 psi max.

If it is possible and easily done, adding a 30 psi valve would buy you some piece of mind.

lucky131969

Thanks for the feedback everyone. I'll install a 30# pressure relief valve on the piping.

EBEBRATT-Ed

Standard heating expansion tanks (Extrol etc) cannot be used on a system with a relief valve that is over 30 psi per ASME code.

not sure about potable water expansion tanks

Gordy

It should be noted that the option of adding a 30psi relief valve in the system. That relief valve location needs to be able to protect the whole system at all times. So think about whether, or not various components have the ability to isolate that relief from parts of the system in certain situations.