Correct discharge for TPR Valve on water heater located inside of home.

Inspection on home built in 1985 today with a gas water heater in the laundry room. I am reasonably familiar with most of the code restrictions of what you can’t do with the discharge but what is the right way to to do it on a water heat located inside? There is no floor drain and I would think routing it the the exterior would be "subject to freezing and would an exterior discharge considered “readily observable
by the building occupants”?

That is where an “indirect waste receptor” comes in.

Thanks guys!.. And now I’ve wasted the last hour reading arguments about proper indirect waste receptors and approved materials. :roll:

Would an exterior discharge be “subject to freezing” if it has proper slope and everything else is correct? Asking from Idaho so it does tend to get a little chilly at times.

I’m in Houston and we don’t have the freezing issue. With an indirect receptor and air gap, should the exterior discharge freeze over. The valve can still discharge water if it needs, though it will eventually overflow.

One method is to discharge into a standpipe connected to the house drain plumbing so long as there is an air gap and the discharge is readily visible. It can even share the same standpipe as the clothes washer, a common configuration for condos.

Give us a bit more info or a photo of the installation of your WH. Where is the WH located? Home have a basement, crawlspace, slab? Is the home a Manufactured/Modular home? I see a lot a creative methods in Minnesota. Not always by-the-book, but effective for the conditions.

I have a city that allows what you have described but I still write it up as PVC schedule 40 plastic has a temp rating of 180 degrees and if the relief valve lifts the water temp will be exceeding the rated temp and can damage a section of the PVC. My thinking is its cheaper to clean up the water than it is to jack hammer a slab floor to repair a drain line

You got me with this one… The TPR valve is not for flowing water, So if it lets go, that means there is a problem and the occupant needs to see it and call a plumber for repair or replacement. If it’s piped to a crawl space or outside, how would anyone know it’s leaking?

Why not just route it 4 - 6 inches off the floor?

Like the Picture from Directions in Post #2

Right, however, #13 says: “not in a manner to cause structural or property damage.” Regardless, in my area, piping it to the floor is the norm. If one is concerned with getting the floor wet (these things go off all the time;-)), I guess a pan and/or drain could be put in.

This is one where I would suggest you go directly to your AHJ and get their position on it. My reason is I have two AHJ’s here in Northern CA that have local codes that allow for discharge designs that allow the line to flow upward. It uses a “Tee” and a Copper tube that goes down for any leaks or seepage from the valve. PM me if you want a copy of their drawing. Remember the LOCAL AHJ has the final say.

I saw that picture, seems to me a great way to direct scalding water straight back up if it discharges.

I am really looking for a general answer for future knowledge as this one had several things wrong so I wrote it up anyway.

I think William is right, I really need to check locally. Idaho usually doesn’t stray far from the national codes but looks like this one has a lot of regional variances.

Here is an additional picture for your viewing pleasure of this one where it routes through the crawl before going outside.

Yes. there are several problems with what is depicted in that picture (material, construction and trapped at least).

What, because there’s a bucket there to test the TPR valve?

Originally Posted by rcooke
Like the Picture from Directions in Post #2

It is critical that discharge pipes meet the following requirements, which can be found in InterNACHI’s Water Heater Discharge Piping mini-course, at A discharge pipe should:

  1. be constructed of an approved material, such as CPVC, copper, polyethylene, galvanized steel, polypropylene, or stainless steel. PVC and other non-approved plastics should not be used since they can easily melt.
  2. not be smaller than the diameter of the outlet of the valve it serves (usually no smaller than 3/4").
  3. not reduce in size from the valve to the air gap (point of discharge).
  4. be as short and as straight as possible so as to avoid undue stress on the valve.
  5. be installed so as to drain by flow of gravity.
  6. not be trapped, since standing water may become contaminated and backflow into the potable water.
  7. discharge to a floor drain, to an indirect waste receptor, or to the outdoors.
  8. not be directly connected to the drainage system to prevent backflow of potentially contaminating the potable water.
  9. discharge through a visible air gap in the same room as the water-heating appliance.
  10. be first piped to an indirect waste receptor such as a bucket through an air gap located in a heated area when discharging to the outdoors in areas subject to freezing, since freezing water could block the pipe.
  11. not terminate more than 6 inches (152 mm) above the floor or waste receptor.
  12. discharge in a manner that could not cause scalding.
  13. discharge in a manner that could not cause structural or property damage.
  14. discharge to a termination point that is readily observable by occupants, because discharge indicates that something is wrong, and to prevent unobserved termination capping.
  15. be piped independently of other equipment drains, water heater pans, or relief valve discharge piping to the point of discharge.
  16. not have valves anywhere.
  17. not have tee fittings.
  18. not have a threaded connection at the end of the pipe so as to avoid capping

I think this is a good way when there is no drain ,
Please tell us how you think it should be handled .

Although I understand that this topic has been discussed a lot, I’m going to weigh in. I will call out PEX if it is used on a water heater discharge pipe. Here is my reasoning. PEX is rated for around 200 degrees and 160 PSI at 70 degrees. For my example, let’s say the TPR valve is rated for 210 degrees or 150 lbs PSI. Seems that PEX should be acceptable. But as anybody knows multiple malfunctions can occur in a single event. Suppose our water heater has a thermostat failure, and TPR valve that is supposed to trip at 210 degrees, does not trip. Now the temperature and pressure inside the water heater continue to climb until the pressure reaches 150 psi at which point the TPR releases. At 150 psi the boiling point of water is around (if my calculations are correct) 350 degrees F. Despite what some people have said, PEX fittings do restrict the pipe size significantly. Just go to Home Depot and measure the interior diameter of a ¾ PEX fitting. Its not ¾ inch. Now you have super-heated water under high pressure entering a restricted pipe with enough temperature to melt that pipe. Anyone in the area could easily be scalded. Now take the same example with copper pipe. The water would be vented to the exterior with very low chance of injury. I understand that a dual failure is unlikely, but it is possible. Were it to occur, the possible ramifications are too great in my opinion to not call it out.

Interesting would you please explain how it gets to the exterior discharge … thanks Roy |C