Thread: Have any of you guys checked the difference in a wh pressure when dialing up the tem

On a water heater tank, the old style, have you ever checked the difference in pressure from the settings of hot to very hot? Say you start by checking the pressure at the front hose bib and record it. Say you have a pressure reducing valve installed and it is set to 60 psi which your gauge confirms. How much would the pressure rise if you changed the temp from hot to very hot? I understand that it is not advisable to set and leave a water heater at the very hot setting due to scalding, and I understand that the hot setting is approximately 120 degrees as stated by the manufacturer. Just curious how much the pressure rises under these circumstances. Is there a formula for calculating the pressure rise?

Originally Posted by Loren Sanders Sr.

On a water heater tank, the old style, have you ever checked the difference in pressure from the settings of hot to very hot? Say you start by checking the pressure at the front hose bib and record it. Say you have a pressure reducing valve installed and it is set to 60 psi which your gauge confirms. How much would the pressure rise if you changed the temp from hot to very hot? I understand that it is not advisable to set and leave a water heater at the very hot setting due to scalding, and I understand that the hot setting is approximately 120 degrees as stated by the manufacturer. Just curious how much the pressure rises under these circumstances. Is there a formula for calculating the pressure rise?

I don't have a specific answer to your question but there was a fairly lengthy discussion regarding installation of Thermal Expansion Tanks, fairly recently. You may glean some information from that thread. The circumstance you described was performed by plumber to a client in a effort to convince them to install a TET. As I recall the pressure on his gauge rose from 60psi to 120psi going from warm/tepid water setting to max. hot.

This may help you to find an answer
Thermal expansion rate of water: Hot Water Expansion Rate & Hot Water Pressure Increase in Hot Water Tanks or Boilers