Fuel Gas Piping and Gas-Fired Appliances
Piping and sizing
Michigan adopts the International Fuel Gas Code (NFPA 54). Gas piping is sized by the longest-length method using the total connected load in Btu/h, the gas's specific gravity and heating value, and the allowable pressure drop. Natural gas is assumed at about 1,000 Btu per cubic foot and specific gravity 0.60 when using the tables. Convert appliance input to flow: a 100,000 Btu/h furnace draws 100 cubic feet per hour. Materials: black steel Schedule 40 with malleable fittings, listed CSST, and copper only where permitted; plastic pipe is not used for gas.
Installation rules that get tested
Support piping and protect it from corrosion and physical damage. Gas pipe may not run through air ducts, return-air plenums, elevator shafts, or concealed locations that are inaccessible. Each appliance needs a shutoff valve in the same room, a sediment trap (drip leg) at the inlet, and a connector not exceeding 6 feet that does not pass through a wall, floor, or ceiling. CSST must be bonded to the grounding electrode system per the manufacturer and code.
Combustion air and venting
Appliances need combustion air from the prescribed indoor or outdoor methods, proper clearances to combustibles, and venting per the category of the appliance. Category I appliances use a draft hood and vertical vent with correct rise and termination; direct-vent appliances use the manufacturer's vent kit. Blocked flue and spillage are the failure modes that cause carbon monoxide incidents.
Testing
The installed system is tested before the meter is set, commonly at 1½ times the working pressure with a minimum of 3 psi held for 10 minutes, using a gauge with the required range. Leaks are found with soap solution or an electronic detector - never a flame.
Worked example
A range rated 65,000 Btu/h plus a 120,000 Btu/h boiler totals 185,000 Btu/h ≈ 185 cubic feet per hour to enter the capacity table.