Gas Piping and Combustion Venting
Sizing gas pipe
The fuel gas code sizes piping by connected load in cubic feet per hour, not by pipe diameter preference. Convert each appliance's input rating to cfh: natural gas is roughly 1,000 Btu per cubic foot, so 100,000 Btu/hr ≈ 100 cfh; propane is about 2,500 Btu per cubic foot. Add all appliances on the run, measure the longest length from the meter or regulator to the farthest outlet, and then read the table with the correct pressure, pressure drop, and specific gravity (typically 0.60 for natural gas, with a 0.5 in. w.c. drop allowed). Manifold pressure at the appliance is commonly about 7 in. w.c. for natural gas and 11 in. w.c. for LP; appliance regulators are set per the appliance listing.
Installation essentials
Provide a shutoff valve at each appliance, a sediment trap or drip leg ahead of the controls, a union or approved connector at the appliance, bonding of the gas piping, and protection of concealed runs. Piping is prohibited in ducts, plenums, elevator shafts, and similar spaces, and concealed unions are not allowed. Test the system with air or inert gas at the code-required pressure - typically not less than 1.5 times working pressure with a minimum around 3 psi - for the required duration before the meter is set.
Venting
Venting follows the appliance category. Natural-draft Category I appliances use listed vents with correct clearances to combustibles (about 6 in. for single-wall, 1 in. for Type B) and correct termination relative to windows, doors, and air intakes. Condensing appliances are commonly vented in PVC or CPVC per the listing, with slope back to the appliance and a condensate drain. Provide combustion air by the prescribed method (open volume or two permanent openings) or by a listed direct-vent arrangement.
Traps
Sizing on one appliance when the run serves several, ignoring the sediment trap, and venting a condensing appliance in the wrong material.