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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!
  • 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.
  • 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.
  • 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.
  • 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'
  • SoundGuy's avatar
    SoundGuy
    Explorer
    Sep 21, 2017
    Atwood water heater relief valve, 1/2", Mfg Part #92655.

    Suburban water heater relief valve, 3/4", Mfg Part #161230.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Sep 21, 2017
    SoundGuy wrote:
    Atwood water heater relief valve, 1/2", Mfg Part #92655.

    That part number is for a 75 psi 1/2" NPT relief valve. Not the one used on typically Atwood RV Water Heater

    There are FOUR (4) different part numbers for Atwood Water heaters.
    These 2 are most common based on year/model
    91604 Relief Valve (150 psi) 1/2” - NPT
    90028 Relief Valve (150 psi) 3/4” - NPT


    These two are less common---mostly used for 'marine applications'
    92655 Relief Valve (75 psi) 1/2” - NPT
    92647 Relief Valve (75 psi) 3/4” - NPT





    Suburban water heater relief valve, 3/4", Mfg Part #161230.


    Atwood.....can be confusing----based on year/model and application (RV/Marine)
    Suburban.....straight forward---one size
  • Dusty_R's avatar
    Dusty_R
    Explorer
    Sep 21, 2017
    Some water heaters have an anode rod in them, which is supposed to prevent water heater tank from rusting out. Some types of water, especially well water, will do this. Remove or replace that anode rod and the rotten egg smell will go away.

    Dusty
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    Sep 21, 2017
    JoshInReno wrote:
    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.


    Lowes, Home Despot or your local hardware will be cheaper than Grainger. Grainger works for specialty items. A T&P valve is not a specialty item.

    Get them from a box store, you can return the unused ones.

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