When a TPR discharge tube is reduced...

rabbitsfoot

When a hot water heater discharge tube is reduced, what is the danger? Have read this shouldn't be done. Thanks.

Jamie Hall

That simply won't do. The problem is that the rating of the valve is dependent on the size of the discharge, among other things, and by reducing the size the valve (particularly to a tiny pipe like that) it will not be able to handle the flow it is supposed to, should it have to operate.

Will this be a problem? Maybe not. Maybe it will be just fine. But you don't have the valve you are required to have any more, and there is a reason they're size the way they are. Why take a chance?

rabbitsfoot

I noticed some water heaters have these valves on the top but other TPR valves are on the side of the tank (near the top). Is either arrangement more prone to sediment blockage?

ChrisJ

The size cannot be reduced because it needs a certain amount of volume to escape all at once. I believe, generally gas heaters have them on the sides because there's other things in the way on top. I would recommend using the location designated by the manufacturer.

I would recommend piping the T&P with rigid copper and use the proper size for the valve. I'd also install a union so the pipe can be removed for inspection and cleaning as well as the replacement of the valve.

No hose connection at the bottom and it should stop a few inches above the floor. I would recommend checking your local codes.

Larry Weingarten

Hi @rabbitsfoot , I agree with all said above. About your question of T&P placement and sediment buildup, it doesn't really matter. What I've found blocks the valve is the action of the anode rod in hard water. It wants to protect the brass, so plates it out with hardness from the water. In my area about one in forty T&Ps is plugged solid, whether it's on the side of the tank or up on top.

Yours, Larry

mattmia2

i remember when there wasn't a separate tapping for the t&p valve and the installer had to put it in the outlet with a tee.

the model code says that the piping from the relief valve has to be rated for the working temp of the fluid in the system. michigan code deviates from the model and says it has to be rated for something like 210 degrees so it has to be metallic in michigan

ChrisJ

mattmia2 said:

i remember when there wasn't a separate tapping for the t&p valve and the installer had to put it in the outlet with a tee. the model code says that the piping from the relief valve has to be rated for the working temp of the fluid in the system. michigan code deviates from the model and says it has to be rated for something like 210 degrees so it has to be metallic in michigan

When I was a kid our water heater had one mounted in the pipe and it was adjustable. I believe that was only pressure though not a t&p

EdTheHeaterMan

ChrisJ said:

When I was a kid our water heater had one mounted in the pipe and it was adjustable. I believe that was only pressure though not a t&p

When I was a kid I walked 5 miles to school in the snow uphill in both directions and they did not even invent relief valves yet.
A quote from my Grand Father.

Steamhead

Whoever did that should not be in the business. That's dangerous, as others have said- get it repiped.

rabbitsfoot

to Larry Weingarten: you must feel lucky after fixing that one in forty... so maybe the hardness of the local water supply has some bearing on the rate at which a valve might be blocked?  Water hardness here said to be 230ppm on average.

EBEBRATT-Ed

I have seen plenty of them reduced to 1/2" and have seen some with a PVC blow off pipe.

Neither one is right in my opinion

rabbitsfoot

So then if water needs to exit this thing in a hurry and it hits that stricture it could be no different than if it were capped off, and rupture. Understood correctly ? I wonder if anyone's seen this very type of arrangement condemned and shut down by some sort of code enforcement entity until brought up to the generally agreed upon standard.

mattmia2

In reality it is usually rated for a 100,000 btu/hr+ burner and at the 40,000 btu/hr burner in a domestic water heater it would likely be able to dissipate enough energy to keep it from exploding through the 1/2" pipe, but it isn't legal.

CPVC or pex may be legal if it is the same size as the valve depending on the jurisdiction.

Larry Weingarten

rabbitsfoot said:

to Larry Weingarten: you must feel lucky after fixing that one in forty... so maybe the hardness of the local water supply has some bearing on the rate at which a valve might be blocked?  Water hardness here said to be 230ppm on average.

Hi @rabbitsfoot , I take quite seriously that saying about the plumber protecting the health of the nation. I've no doubt that many here have saved lives. Water quality in TDS here (Central California) ranges from around 150 ppm to 2000 ppm, so there is a lot of hard water. My preferred approach to plumbing a relief valve is brass nipple in the valve, then copper flex line, then hard copper pipe to a safe location. That makes it easy to check and replace the valve if needed. I read that hard water is considered to be 200 ppm or higher, so you have it!

Yours, Larry

rabbitsfoot

one or two more

WMno57

I had a circa 1970 Rheem water heater in a former home that was 35 years old and working fine. That one was gas and hard water with a water softener. Can anyone tell how old this one is by the serial number?

Larry Weingarten

Hi, The serial number on this begins C98, so to me this says it was made on March of 1998. Hope the anodes have been checked!

Yours, Larry

pecmsg

InLarry Weingarten said:

Hi, The serial number on this begins C98, so to me this says it was made on March of 1998. Hope the anodes have been checked! Yours, Larry

Who cares
at that age it’s done. Replace it!

JUGHNE

I did not see anyone mention it, but just some instruction that come with WH's concerning T&P valve discharge....full size of course but no threaded end on the discharge drop pipe.....looking at the flare nut on that 1/2" OD copper it would be tempting to put a plug in there to stop that annoying drip.
Same for a 3/4" pipe thread left on the end.

And not to tee two water heaters together for a common discharge pipe.

rabbitsfoot

I believe they actually went by the first four numbers of the serial number... (mm/yy) and if a little of that ink is missing, then 0985101633 becomes September, 1985

Larry Weingarten

Hi, @rabbitsfoot , You nailed it! State can use the letter/year code, but Rheem does the numerical month/month.. year/year.

Yours, Larry

JohnNY

This is one of those threads that I skim through and just shake my head. @rabbitsfoot go buy some ¾" sharkbite fittings, 5 feet of pipe and a hacksaw and fix that remarkably terrible situation you've got there.

Intplm.

And when you do change the relief valve discharge tube to the correct size (3/4 inch I.D. copper tubing.) You will be able to re-use that new discharge tube when you replace that water heater. Which you most likely will need to do in the very near future.