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Thread: Shutoff Valve in Hot Water Line of Water Heater

  1. #1

    Default Shutoff Valve in Hot Water Line of Water Heater

    Is there any model code, manufacturer's installation instruction, or just plain reason that prohibits the installation of a shutoff valve in the hot water line coming out of the top of a water heater?

  2. #2

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    Not that I know of. Many HW tanks have shutoffs at both the inlet and outlet.

  3. #3
    In the Trades Gary Swart's Avatar
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    You should put a valve on the hot water line so that you can flush the tank without washing crud into it. One on the cold intake side isn't so useful, but with one, you could remove the tank without turning off the entire house water, and it's cheap enough to do. I use full flow ball valves.

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    Moderator & Master Plumber hj's Avatar
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    Default valve

    Some, not "many", water heaters have valves on both side. I run across ONE every ten years or so. And the one on the cold side is REQUIRED by all codes, even though someone says it is "not useful".

  5. #5

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    Most of my previous experience is with larger tanks used in apartment buildings. They almost always have two shutoffs.

    Recently, however, most of the residences I have worked in have zero shut-offs, which means no water until their tank is replaced (or until I install the CW shutoff).

  6. #6
    Senior Robin Hood Guy Ian Gills's Avatar
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    Are all of you completely mad? Or is it 1 April?

    Even a DIYer knows this one, which says something.

    It is incredibly dangerous and absolutely against code to have a shut-off on both the inlet and outlet of a hot water heater. If both are closed, the WH relies completely on the proper functioning of the PRV to deal with pressure/expansion changes and faults if the heater is left on.

    If the PRV fails, then we start to see explosions of the type some of you post links to on this site every now and again.

    My neighbor has valves on both the inlet and outlet of his WH and I live in fear. Say he shuts them both off and forgets and the PRV fails?

    Shut-offs on WHs should only be installed on the cold side. That way, the fixtures and fittings (think washer hoses) of the hot supply will also take the strain of any increase in pressure should the PRV fail and there is fault with the WH. There is therefore less chance of a boom.

    How many bombs are you guys making?

    LONG LIVE D.I.Y.
    Last edited by Ian Gills; 12-16-2008 at 11:52 AM.

  7. #7
    In the Trades Gary Swart's Avatar
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    Regarding my statement that the valve one the "cold side wasn't as important etc.. My bad!! I certainly meant the valve on the HOT side was not as important as on the intake (cold) side. Thanks to HJ for catching my error!

  8. #8
    Senior Robin Hood Guy Ian Gills's Avatar
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    I cannot believe we are still sitting here entertaining this very idea.

    Am I dreaming?

    Or have I died and been reincarnated into a new world where there is a different plumbing code as well as a new law of physics?

    Or both?

    Two shut-offs on the outlet and inlet of a WH equals a potential boom. Period. Don't do it. Shut-offs, like expansion tanks, should only be installed on the cold side.
    Last edited by Ian Gills; 12-16-2008 at 12:27 PM.

  9. #9

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    Take it easy, man. You are the one about to explode.
    The only reason anyone would shut off those valves is to do maintenance or to replace the tank.

    And, even if both valves are closed while the tank is fired up, in order for it to become a bomb, both the thermostat and the T&P valve would have to fail.

  10. #10
    Senior Robin Hood Guy Ian Gills's Avatar
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    I am cool.

    Just trying to invoke some passion and debate.

    I get as good as I give on here anyway.
    Last edited by Ian Gills; 12-16-2008 at 02:29 PM.

  11. #11
    Plunger/TurdPuncher kingsotall's Avatar
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    aaronm, is there any particular reason you were asking or were you just wonderingż

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    DIY Senior Member Probedude's Avatar
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    Quote Originally Posted by Ian Gills View Post
    I am cool.

    Just trying to invoke some passion and debate.

    I get as good as I give on here anyway.
    Think of it this way in regards to the water heater being a bomb if the inlet and outlet were shut off and the TPV failed
    - how is this different than if the inlet were shutoff and no other hot water fixture in the house was turned on? It's still a closed system.

  13. #13
    Senior Robin Hood Guy Ian Gills's Avatar
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    You have washer hoses, copper fittings and all sorts of other fixtures that will probably fail before the water tank does.

    Not to mention you might notice the problem in the chance you open a tap.

  14. #14

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    I have a shutoff valve on the cold side as well as the hot side of my water heater. The T&P valve is between the hot water output of the water heater and the hot water shutoff valve.


    Works fine!

  15. #15
    Senior Robin Hood Guy Ian Gills's Avatar
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    Again, I raise an objection.

    If a licensed plumber installed a shut-off on the hot side of my tank I would be extremely disappointed, and tell him to remove it.

    Of course he wouldn't because they all want to save a few bucks on fittings.

    But more importantly it is against code.

    I am more than slightly surprised that a few of the pros around here are not jumping in and backing me up on what is a basic safety issue.
    Last edited by Ian Gills; 12-18-2008 at 02:00 PM.

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