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T&P hot water heater valve discharge pipe

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Is a 150 psi T&P hot water heater valve compatible with 100 psi-180F PVC in/out piping?
asked in Gas Water Heater by cwhudson (120 points)
edited by darekrudy
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1 Answer

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Hi cwhudson,

PVC is not permitted to be used as a TPRV (T&P) discharge pipe. You can find the details about the installation in my post - http://checkthishouse.com/16/water-heater-tpr-safety-valve.html or by visiting the IRC (International Residential Code) online.

The section below is a list of requirements from the IRC page (13 items) and a table listing pipe material types that are permitted to be used as a TPRV valve discharge pipe (both referral links are below the table.

Keep in mind that some jurisdictions may put further restricions on those requirements below.


P2803.6.1 Requirements for discharge pipe. The discharge piping serving a pressure-relief valve, temperature relief valve or combination valve shall:
1. Not be directly connected to the drainage system.
2. Discharge through an air gap located in the same room as the water heater.
3. Not be smaller than the diameter of the outlet of the valve served and shall discharge full size to the air gap.
4. Serve a single relief device and shall not connect to piping serving any other relief device or equipment.
5. Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor or to the outdoors.
6. Discharge in a manner that does not cause personal injury or structural damage.
7. Discharge to a termination point that is readily observable by the building occupants.
8. Not be trapped.
9. Be installed to flow by gravity.
10. Not terminate more than 6 inches (152 mm) above the floor or waste receptor.
11. Not have a threaded connection at the end of the piping.
12. Not have valves or tee fittings.
13. Be constructed of those materials listed in Section P2905.5 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.


P2905.5 Water-distribution pipe. Water-distribution piping within dwelling units shall conform to NSF 61 and shall conform to one of the standards listed in Table P2905.5. All hot-water-distribution pipe and tubing shall have a minimum pressure rating of 100 psi at 180°F (689 kPa at 82°C). 




Brass pipe


Chlorinated polyvinyl chloride (CPVC) plastic pipe and tubing

ASTM D 2846; ASTM F 441; ASTM F 442; CSA B137.6

Copper or copper-alloy pipe

ASTM B 42; ASTM B 302

Copper or copper-alloy tubing (Type K, WK, L, WL, M or WM)

ASTM B 75; ASTM B 88; ASTM B 251; ASTM B 447

Cross-linked polyethylene (PEX) plastic tubing

ASTM F 876; ASTM F 877; CSA B137.5

Cross-linked polyethylene/aluminum/cross-linked polyethylene (PEX-AL-PEX) pipe

ASTM F 1281; ASTM F 2262; CSA B137.10M

Cross-linked polyethylene/aluminum/high-density polyethylene (PEX-AL-HDPE)

ASTM F 1986

Galvanized steel pipe


Polyethylene/aluminum/polyethylene (PE-AL-PE) composite pipe

ASTM F 1282

Polypropylene (PP) plastic pipe or tubing

ASTM F 2389; CSA B137.11

Stainless steel (Type 304/304L) pipe

ASTM A 312; ASTM A 778



answered by darekrudy (21,730 points)