Water Heaters and Fuel Gas Piping
What the exam tests
This domain covers water-heater installation, temperature and pressure relief, venting, combustion air, thermal expansion, and fuel-gas piping. Safety devices and gas connections are heavily tested.
Core rules
- A temperature and pressure relief valve must be rated for the heater and piped full size, without a valve or trap, to a safe discharge point.
- Gas piping needs a shutoff, sediment trap, approved connector, support, and a leak test before use.
- Water heaters need combustion air and proper venting; do not use PVC flue pipe on a gas appliance unless listed for that use.
- A closed potable system needs thermal expansion control.
- Follow the adopted fuel-gas code for pipe sizing and test pressure.
Worked example
A 40-gal heater must raise water 100 degrees F. Water weight = 40 x 8.33 = 333 lb. Btu required = 333 x 100 = 33,300 Btu. At 80% efficiency, input = 33,300 / 0.80 = 41,625 Btu/h. A 40,000-Btu/h burner is close, but recovery takes slightly more than an hour; size from the recovery table, not tank volume alone.
Traps that cost marks
Capping or plugging the T&P valve; reducing the discharge pipe; running the discharge uphill or trapping it; omitting the sediment trap; using a flexible connector through a wall; ignoring expansion on a closed system.