What Heater Thingamajig

[Ian Gills]

I do not see why any of this would not be dealt with by the ordinary pressure relief valve, which this is obviously not (I assume the ordinary one remains on the heater). Is it to regulate smaller (i.e. less dramatic/dangerous) pressure increases?

[Marc D. Shunk]

Originally Posted by Ian Gills

I do not see why any of this would not be dealt with by the ordinary pressure relief valve, which this is obviously not (I assume the ordinary one remains on the heater). Is it to regulate smaller (i.e. less dramatic/dangerous) pressure increases?

Bingo. The required TPR is for worst case. Any additional pressure relief is to maintain or enhance system performance. These optional valves are available in several more pressure settings, as low as 75 and 80 lbs. THey were required by at least one PEX manufacturer about 10 years ago, but I believe that requirement has evaporated now.

[brepanshek]

I normally install an expansion tank on the cold water supply line to tank for thermal expansion. So what your saying is that this valve does the same function as a expansion tank? If you were to install a new waterheater, can you just use this watts valve instead of a expansion tank? Am I understanding this or am I wrong?