How is system pressure

Luv'nsteam

developed in a hot-water heating system?  Is it inlet pressure, pressure developed by the circulator pump, resulting pressure from the water being heated, all of the above, something completely different?



Thanks,

Mike

Mike Kusiak_2

All of the above

All three contribute to the system pressure. First there is the static fill pressure which is produced by the pressure reducing fill valve. It is basically a pressure regulator which establishes a pressure of about 15 PSI at the bottom of the piping. In taller buildings it may be higher. You want to have at least 4 or 5 PSI at the topmost point in the system.



Second, there is the dynamic pump head or pressure which causes the water to circulate through the system. This pressure will either add or subtract from the static pressure, depending on the pumps location relative to the expansion tank.



Third, a temperature rise of the water in the system will cause it to expand, compressing the air in the expansion tank and causing the system pressure to rise proportionally.



So, the system pressure is the sum of these individual pressures, each of which may vary depending of the location and operating state of the system.