Temperature Pressure Relief (TPR) Valves
UPC 608.5 Relief valves located inside a building shall be provided with a drain, not smaller than the relief valve outlet, of galvanized steel, hard drawn copper piping and fittings, CPVC, or listed relief valve drain tube with fittings which will not reduce the internal bore of the pipe or tubing (straight lengths as opposed to coils) and shall extend from the valve to the outside of the building with the end of the pipe not more than two (2) feet (610 mm) nor less than six (6) inches (152 mm) above the ground or the flood level of the area receiving the discharge and pointing downward. Such drains may terminate at other approved locations. No part of such drain pipe shall be trapped or subject to freezing. The terminal end of the drain pipe shall not be threaded.
“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
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
P2904.5 or materials tested, rated and approved for
such use in accordance with ASME A112.4.1. 438″
Long story short:
Don’t reduce the valve. They are generally 3/4″.
Don’t make the drain line out of materials that cannot handle heat (PVC is rated for hot water).