Water Heaters and Related Equipment
What this domain tests
Installation, relief protection, venting, and combustion air for storage and tankless water heaters, plus the safety devices inspectors look for first.
Core rules
- Every storage water heater needs a temperature-and-pressure relief valve rated no higher than 210°F and 150 psi, installed in the top 6 inches of the tank or as the manufacturer directs, with no valve, cap, or plug on either side.
- The discharge pipe stays the full size of the valve outlet, is made of material rated for 210°F (copper or CPVC, not PVC), runs as short and straight as practical, is not trapped, and terminates within 6 inches of the floor or outside where it will not cause injury.
- A drain pan 1½ inches deep with a ¾-inch drain is required where leakage would cause damage and wherever the heater sits in an attic or above a ceiling.
- Where a check valve, pressure-reducing valve, or backflow preventer creates a closed system, thermal expansion needs a listed expansion tank; a T&P valve is not a substitute.
- Gas heaters: sediment trap, listed shutoff valve, listed draft hood or power vent, vent connector sloping up toward the chimney, and combustion air by the two-permanent-opening method or direct vent. An appliance in a garage needs ignition sources 18 inches above the floor.
- Electric heaters need a disconnecting means within sight and correctly sized branch protection.
Worked example
A 50-gallon gas heater with a ¾-inch T&P outlet is piped in ½-inch copper to a floor drain 20 feet away. Two failures: discharge reduced from ¾ to ½ inch, and a long run that sags and traps water. The fix is full-size ¾-inch copper with continuous fall to a safe termination.
Traps that cost marks
Plugging a leaking T&P valve instead of finding the cause; using PVC for relief discharge; forgetting the expansion tank on a closed system; omitting the pan above a finished ceiling.