Section 422.1/Water Heater Installation
UPC 422 covers water heater T&P relief, drain pans, seismic strapping, and discharge piping requirements.
Water heaters must be equipped with a temperature and pressure (T&P) relief valve set at a maximum of 210 degrees F and 150 psi. The T&P relief valve discharge pipe must terminate at a point where the discharge is observable (within 6 inches of the floor or to an approved indirect waste receptor). The discharge pipe must not be smaller than the valve outlet, must not be trapped, and must not discharge where it can cause damage. A drain pan is required under water heaters installed in locations where leakage would cause damage. Seismic strapping is required in seismic design categories C through F.
Why this section exists
A water heater without a functioning T&P relief valve can overheat and explode. The T&P valve is the last line of defense against catastrophic failure. The discharge pipe must terminate where the hot water discharge is visible (to alert the building occupant that the valve has opened, indicating a malfunction) and where it will not scald anyone. Drain pans prevent water damage from slow leaks. Seismic strapping prevents the heater from falling during an earthquake, which can rupture gas lines and water connections.
What plan reviewers look for
Plan reviewers check the plumbing drawings for the T&P relief valve and discharge pipe routing at every water heater. They verify the discharge termination point and that the pipe is not trapped or reduced in size. They check for drain pans where required (typically attics, closets, or any location above finished spaces). In seismic areas, they verify strapping details.
Common violations
Related UPC requirements
Section 608 covers T&P relief valve requirements in detail. Section 603 covers water supply sizing that feeds the water heater. NFPA 54 covers gas piping and venting for gas-fired water heaters. The manufacturer's installation manual provides additional requirements for clearances and combustion air.