Confused About Pressure

joe lambert_2

I am a homeowner with a question about the pressure of the circulating hot water system in my home.  The building from basement to top radiator is around 50 ft. tall.  I know that the small circulation pump does not have to provide much pressure because the water is going up and then down, with no net gain or loss in head. 

My question is the set pressure for the system (and the city water PRV valve).  Should this be a bit over the pressure required to fill my highest radiator, or about 22 psi?

Big Ed_4

Pressure Reducing Valve

Your house pressure should be adjusted much higher, around 50-60 pounds. The pressure reducing valve on the heating system should be set to 22 pounds. You need enough pressure in the system to matain a column of water to fill the system , plus two pounds for safety . There should be another pressure reducing valve on the boiler...

Mike Kusiak_2

Correct

The pressure setting of the PRV with the system cold should be adjusted so that it will raise the water to the highest point in the system, plus a few PSI to insure a positive pressure at that point. 21.6 PSI will raise the water 50 feet, but does not give you any residual pressure, so you might have to go a few PSI higher. If your boiler relief valve is set for 30 PSI  it doesn't leave too much reserve for thermal expansion, so you may have to compromise the setting toward the lower limit.

joe lambert_2

Clarification

Thanks Big Ed, but sorry for the confusion.

The PRV I was talking about is the one going into the boiler, there is no PRV for the domestic water supply to the house, that pressure is fine.

Your answer is what I thought, so I try to set the pressure at about 25psi, it is just a bit close to the 30 psig relief!

Big Ed_4

Pressure

Yes your very close ... I would want to see extra expansion capabilities and the lowest temperture setting needed to heat the building. I would be looking for no rise on pressure with temperture rise on the system ..