Relief Valve Sizing for Indirect Water Heaters

From time to time contractors question the proper sizing for temperature and pressure relief valves used with indirect water heaters. It goes without saying that for safety reasons, the proper relief valve must be installed and maintained. The following are recommendations from the three vendors we sell:

Peerless PP40 uses a Watts 100Xl-8
PP60,80 or 120 uses a Watts 40XL-8
Weil McLain Plus 30/40/60 would use a Watts 100XL-8
Plus 80/120 would use a Watts 40XL-8
Amtrol 41Z uses a Watts 100XL-8

As always be sure that these factory recommendations do not conflict with local codes.