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Thread: dual T&P valves a good idea?

  1. #1
    DIY Member northman's Avatar
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    Default dual T&P valves a good idea?

    doing a remodel where I have extensively re-worked the plumbing. Water heater is in a walk-out basement, was plumbed with the usual 150 psi relief valve out the side of the tank, piped down toward the floor. There was also a 125 psi relief valve on the hot pipe shortly after exiting the tank, plumbed up and outside through the nearby exterior wall.

    Is this a good idea, should I go a little out of my way to incorporate this into my new piping scheme? Or should I just keep the 150 psi valve and call it good?


    Greg

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    I'd probably take it out. It may have been added as a pressure limiter device for a valve(s) that didn't like the high pressure if the system is closed and doesn't have an expansion tank. It is a bandaid. A properly designed system shouldn't need one.

    Do a search here on expansion tanks and see if you need one. If you do, then since you're changing things, you might as well do it right.

    If your static pressure is too high, you should have a prv. If you have a prv and/or you have a check valve in the water supply, you also need an expansion tank. the proper place for that is on the cold side of the WH somewhere (not on the hot side where it would work, but the heat would make it fail sooner).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Member northman's Avatar
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    Default now have a PRV/expansion tank

    wasn't sure if the 125 psi relief was common or not. The previous owner had a solar panel/pre-heat system with all the attending pumps/valves/solenoids for the hot water that was defunct and is now gone. I wasn't sure if the extra T& P had something to do with that or not.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It could be that the collectors couldn't handle the higher temp or pressure. Since it is gone, there is no good reason I can think of.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Engineer Furd's Avatar
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    My house (built in 1987) has a T&P valve plumbed into the hot water supply line just as yours. I always assumed it was in case some bozo didn't install one on the heater itself.

    I know that many years ago water heaters were not always fitted with a safety relief valve tapping and it was necessary to install a tee on the hot outlet in order to fit the T&P valve.

  6. #6
    Forum Admin, Expert Plumber Terry's Avatar
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    There were some inspectors in 1987 and earlier that required a 125 PSI on the incoming cold line.

    In the situation mentioned above, where there is no drain for the water heater relief, except into a bucket, they sometimes add a 125 PSI high enough in the system so that it can be drained by gravity.

    At any rate, the water heater should always have a T&P installed.

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