Fuel Gas Piping and Appliance Connections
Pipe sizing
Gas sizing uses the longest-length method: measure from the meter to the most distant appliance, add the developed length of that run (including fittings allowance), and enter the sizing table with the total connected load. Convert Btu/h to cubic feet per hour by dividing by the heating value of the gas, roughly 1,000 Btu per cubic foot for natural gas. Low-pressure natural gas systems are designed around about 7 inches water column with a 0.5-inch allowable drop; propane runs near 11 inches water column.
Materials and installation
- Metallic pipe, listed CSST with required bonding, and approved connectors. Appliance connectors are limited in length (commonly 6 feet), must not be concealed, and must not pass through walls, floors, or ceilings.
- A shutoff valve serves each appliance, and a sediment trap (drip leg) is installed at the appliance connection.
- Piping through framing gets protection plates; piping is supported and protected against corrosion and physical damage.
- Testing: systems at low pressure are commonly air-tested at a minimum of 3 psi for 10 minutes, or at the pressure the code edition specifies.
Appliances
Appliances need combustion air, venting per the listing, and clearance from combustibles. Ignition sources in garages are elevated above the floor, and flammables are kept clear.
Worked example
A furnace at 200,000 Btu/h and a water heater at 50,000 Btu/h total 250,000 Btu/h. Divide by 1,000 Btu/ft³ to get 250 ft³/h. With a 60-foot longest run, enter the table at 250 ft³/h for 60 feet; the intersection gives the minimum pipe size. The graded steps are the Btu-to-cubic-foot conversion and using the longest run - never the shortest.
Traps
- Sizing from the shortest run instead of the longest.
- Concealing a flexible appliance connector.
- Omitting the sediment trap.
- Skipping the bond on CSST.