Water Heater

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    • #279699

      I am a part time Plbg. Insp. and looked at a remodel job today and on the water heater about 12″ above on cw. was a PRV , I told the Plumber to take it off because I thought when hot water expanded it would give him trouble, what do you Plbg. think.

    • #301492

      how would it give him a prolem?

    • #301493

      He should have to install a thermal expansion tank between the PRV and tank if it was to stay.

    • #301494

      I’ve seen plumbers install expansion tanks on H2o heaters about as often as I’ve seen pigs fly, which aint that often. And most inspectors won’t require it, at least here. It’s a great idea to do so but unfortunately, to keep costs down and stay more competitive, they generally don’t.
      As far as the PT valve causing problems I don’t understand what you are saying as far as a PRV installed on the CW…??? Does CW in this case mean the cold water inlet line? Why in the world would he install one there? Sorry that just makes no sense to me.

    • #301495

      PRV’s located that close to the water heater is either a incorrect installation, or the PRV couldn’t be installed at the main line entrance for whatever reason.

      When PRV’s are installed that close to a water heater, unless the main line is in the same area as heater, they don’t realize that the water line has branch offs that leaves the other lines unprotected by the PRV.

      Expansion tanks are code in Ohio, Code in Kentucky on new installs due to a double-check valve assembly in the meter pits.

      A PRV creates a closed system in a potable water system, the thermal expansion has nowhere to go, and even if you use a PRV with a thermal expansion bypass, it has to reach 135 psi before it opens. If your outside main pressure is higher than 135, forget having thermal expansion protection.

      I always tell homeowners to follow the idea of the pot on the stove with water in it with a lid. Heat that water and the lid wants to come off. No difference between that situation and the hot water generated by a water heater.

      Thermal expansion robs you of the protection of the PRV if you don’t allow a buffer zone for the thermal expansion to go to. The very reason the expansion tanks do a good job of allowing for it.

      Any house you go to, put your hand on the cold water inlet supply of the water heater after it has cycled. You will find that hot water is travelling back up the cold water inlet line due to expansion of water molecules.

      I don’t care much for those new cold water shutoffs with built-in thermal expansion valves. For the very reason that it works like a T&P, and we all know that those valves will eventually seize up from either lack of use, or age.

      Watts, manufacturer of numerous applications relating to pressure reducing valves or thermal expansion products explains in more detail the reasons for such guidelines enforced in numerous areas across the globe.


      “Your best interest is secured by making the right decisions the first time.”

    • #301496

      Awesome post, thank you.

    • #301497

      I should add, that many times, the biggest challenge to getting an expansion tank on when replacing a water heater that already exists is space. It just is’nt there many times. And trying to explain to a homeowner that this and this and this needs to be done to create space for a tank or to fabricate one on somewhere, and will take amount more time and material, is like trying to sell them oceanfront property in Arizona.

    • #301498

      You probably should require them to install a prv at the main line and an exp tank for the water heatr. They must have had a high pressure problem at one time to have a PRV in the first place. You probably already know most codes in the US require the PRV if inlet pressure exceeds 80 psi.

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