Forum Discussion

JoshInReno's avatar
JoshInReno
Explorer
Sep 21, 2017

Water Heater Pressure Relief Valve Outlet Size?

I have a stinky (mild rotten egg smell) water heater on my trailer that I need to deodorize with hydrogen peroxide. I am thinking of filling the water heater through the pressure relief valve. But I don't know the thread size to buy to appropriate fitting.

This is what I am trying to avoid doing:



Unfortunately I can't do much by trial and error because the trailer is at a remote campsite. The nearest hardware store is 80+ miles each way. The campsite is also 4 hours from my home. I am going up this weekend to get this and a few other projects done but time is very limited. I really don't want to pull the valve from the water heater if I can avoid it.

I guess the question is: are the outlets a universal size or should I bring a selection of sizes? I'm guessing 1/2"? NPT I'm assuming?

Thanks!
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Sep 21, 2017
    Suburban uses a 3/4" NPT

    Atwood uses a 1/2" NPT IF it is a 2003 and older model
    Atwood uses a 3/4" NPT IF it is a 2004 and newer model


    Really don't need any fittings, adapters etc

    Just remove T&P Relief Valve and pour vinegar (4 gal to 2 gal water) or Hydrogen Peroxide solutions in thru opening using a FUNNEL'
  • JoshInReno's avatar
    JoshInReno
    Explorer
    Sep 21, 2017
    SidecarFlip wrote:
    It's a standard box store / hardware store T&P valve just like you have on your residential HWH. One size basically fits all.


    Well that's why I asked. I'm going through my handy Grainger catalog here and I'm seeing valves with an outlet size of 1/2, 3/4, 1 and even larger. I'm not seeing much consistency.

    I think I'm just going to take 3/8, 1/2 and 3/4 fittings to be safe.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Sep 21, 2017
    Until a few years ago, Atwood used a 1/2" t&p valve, though I believe the outlet was 3/4" Not certain though, and my stock is in a moving container at the moment, so I cannot check.
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    Sep 21, 2017
    It's a standard box store / hardware store T&P valve just like you have on your residential HWH. One size basically fits all.

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