Pipe Sizing, Installation, and Pressure Testing
Domain 4 tests pipe sizing, installation details, and pressure testing. You must calculate the connected load, select the correct table column, account for equivalent length, and prove the system is leak-free without damaging appliances or regulators.
Sizing method
Start with the appliance input ratings in Btu/h or kW. Add all connected appliances. Measure the longest run from the meter or regulator to the farthest appliance, then add equivalent length for fittings and valves. Use the adopted sizing table for the gas, specific gravity, and allowable pressure drop. Increase diameter rather than exceed the table.
Installation details
Provide a shutoff valve, union, sediment trap (drip leg) at each appliance, and proper support. Protect piping from corrosion, physical damage, and freezing. Use approved materials and joining methods. Do not conceal unions or valves in inaccessible locations.
Pressure test
Isolate the system and test at the pressure and duration required by the adopted code, commonly 1.5 times the maximum operating pressure and not less than the code minimum. Use a calibrated manometer or gauge; never use a flame. Record the test pressure, duration, and result.
Worked example
A furnace rated 60,000 Btu/h and a water heater rated 40,000 Btu/h give 100,000 Btu/h connected load. The longest run is 50 ft with fittings adding 10 ft equivalent, so use 60 ft. At 0.5 in w.c. drop and natural gas, a 1/2 in line is marginal; the 3/4 in column covers the load, so select 3/4 in and verify against the actual table.
Traps
- Sizing on a single appliance instead of total connected load.
- Ignoring equivalent length of elbows and valves.
- Testing with the appliance connected when the code requires isolation.
- Using a low-resolution gauge that cannot show the required test pressure.
- Omitting the sediment trap or shutoff valve.