What is the Correct Hot Water Expansion Tank Pressure
I realized as I was reading through the B&amp;G design guide above what I think the answer is. The 12 PSI is necessary for a two story building on a closed loop hydronic system. Most household boilers are limited to 30 psi before the pressure relief valve will open. So if that system were sized for the 60ish psi, you can probably imagine that there would be some issues. An expansion tank for a hot water system, on the other hand, WOULD be charged to the line pressure since it is directly connected to the incoming cold water line.