Water Heater Pressure Relief Valve Outlet Size?

[JoshInReno]

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]

cpaulsen wrote:

wa8yxm wrote:
There are two sizes common 1/2 and 3/4. but on RV's only the 1/2 is used.

Mine is 3/4".

Shot that in the foot.... 2 times., make it 3. My Sub is 3/4 as well.

[cpaulsen]

wa8yxm wrote:
There are two sizes common 1/2 and 3/4. but on RV's only the 1/2 is used.

Mine is 3/4".

[Johnny_G1]

Just replaced one, Atwood 1994 model, 1/2 in, newer one's can take 3/4 in and that was from a RV dealer in Whitehorse this summer, $39.00 for the 1/2 in one.and that was in my 5th wheel.

[Old-Biscuit]

wa8yxm wrote:
There are two sizes common 1/2 and 3/4. but on RV's only the 1/2 is used.

Not so....
Suburban uses a 3/4" NPT

Atwood used two sizes......1/2" NT & 3/4" NPT depending on year/model

[wa8yxm]

There are two sizes common 1/2 and 3/4. but on RV's only the 1/2 is used.

[SidecarFlip]

Oooops.

[SidecarFlip]

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.

[Dusty_R]

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

[Old-Biscuit]

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

[SoundGuy]

Atwood water heater relief valve, 1/2", Mfg Part #92655.

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

[Old-Biscuit]

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]

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]

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]

It's a standard box store / hardware store T&P valve just like you have on your residential HWH. One size basically fits all.