What is the proper water pressure setting for a pressure-reducing valve or water feeder valve on a Hot Water Heating System?

What is the normal operating pressure of a hot water heating system boiler? Hydronic heating systems (hot water) typically operate at about 12 psi cold and see a pressure increase to somewhere just under 30 psi when the system is at maximum temperature. If you set the water feeder pressure too high it's likely that when the boiler heats-up to operating temperature, the water pressure will exceed the safety limit (30 psi) and the boiler relief valve will open to discharge excess pressure and water. Because a hydronic heating system's circulator pump has little "lift" capacity (it just pushes the water around the loop of boiler and heating piping and radiators), the heating system depends on its internal water pressure to lift hot water to radiators (baseboards, or convectors) on upper floors in the building. A higher building may therefore need higher heating system water pressure in order to be able to circulate heat adequately to upper floors. The sketch, courtesy of Carson Dunlop, ...  more