Water Heaters and Hot Water Supply
Water Heaters and Hot Water Supply
This domain tests safe installation, venting, relief protection, and hot water distribution. Expect questions on T&P valves, expansion, combustion air, and recirculation.
Core rules
- Every storage water heater needs a temperature and pressure relief valve; the discharge pipe must be the same size as the valve outlet, not reduced, not trapped, and terminated within 6 in of the floor or at a safe point.
- A drain pan is required where leakage would cause damage; the pan drain must discharge by gravity to an approved location.
- Gas water heaters need combustion air and proper venting: Category I appliances use a vertical vent with slope, while Category III and IV appliances use listed venting and condensate management.
- A closed system needs a thermal expansion tank; a recirculation system needs a check valve and balanced return.
- Set storage temperature to control Legionella risk while limiting scald; use mixing valves where required.
Worked example
A 40 gal gas water heater has a T&P valve rated 150 psi and 210 degrees F. The discharge pipe is 3/4 in, full size, and ends 4 in above the floor. That is acceptable. If the installer reduced the pipe to 1/2 in or installed a shutoff valve, the relief path would be restricted and the installation would fail.
Traps that cost marks
Plugging a T&P valve, running the discharge uphill or into a trap, omitting the drain pan, and venting a Category I heater with a sagging flue.