Section 504.1/Water Heater Installation
IPC 504 covers water heater T&P relief valves, discharge piping, drain pans, expansion tanks, and seismic strapping.
Water heaters must have a temperature and pressure (T&P) relief valve rated at a maximum of 210 degrees F and 150 psi. The T&P valve discharge pipe must terminate within 6 inches of the floor or to an indirect waste receptor and must not be smaller than the valve outlet (typically 3/4 inch). The discharge pipe must not be trapped, threaded, or plugged at the termination. A drain pan with a minimum 3/4-inch drain is required under water heaters installed where leakage could cause damage. An expansion tank is required on closed-loop systems (systems with a backflow preventer on the supply) to accommodate thermal expansion without triggering the T&P valve.
Why this section exists
A water heater without a functioning T&P relief valve can build pressure until the tank ruptures explosively. The T&P valve is the last line of safety defense. The discharge pipe must terminate where the hot water is visible (to alert occupants of a malfunction) and where it cannot scald anyone. Expansion tanks prevent nuisance T&P valve discharge on closed systems where thermal expansion has nowhere to go. Drain pans catch slow leaks from corroded tanks before they damage the building.
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 location (visible, not into a wall cavity). They check for a drain pan where required (above finished spaces). They check whether the water supply has a backflow preventer that creates a closed system requiring an expansion tank. They verify seismic strapping in applicable seismic zones.