"Donna Ohl, Grady Volunteer Coordinator" wrote:

BTW, where does the 150 psi come from?
I thought incoming water was about 80 psi.
Does just the fact we're heating the water raise the pressure?
Why? It's only 120 degrees (merely hot); not 212 degrees (boiling).

Does the pressure of the hot water rise to 120 psi while the pressure of
the cold water remains at 80 psi?

Water expands when heated... Older systems allow that pressure to go back into
the supply line towards the street. newer systems have check valves.