Gas Fitting: Piping, Materials, Sizing, and Pressure Testing
The framework
Massachusetts gas work is 248 CMR 5.00, which adopts and amends the National Fuel Gas Code. Only a licensed gas fitter may install gas piping, and the work needs a permit and inspection like plumbing.
Sizing method
Gas sizing uses the longest-length method. Convert every appliance's input to cubic feet per hour: natural gas is roughly 1,000 Btu per cubic foot, so a 100,000 Btu/hr appliance draws about 100 CFH; propane tables differ and depend on specific gravity and pressure. Then find the longest run from the meter or regulator to the farthest appliance - adding a range at the end of a run lengthens the longest length for the whole system and can force every section to be re-sized. Use the pressure column matching your system: low pressure (inches of water column) versus elevated pressure with a regulator at the appliance.
Materials and details
Schedule 40 black steel with malleable fittings is the baseline; CSST, copper, and plastic each carry listing and qualification limits, so do not assume a material is acceptable just because it is sold for gas. Every appliance connection generally needs a gas cock, a union or approved connector, and a sediment trap (drip leg) ahead of the controls. Pipe must be supported, protected from physical damage and corrosion, and bonded where CSST or the electrical code requires it.
Testing
Before cover-up and before turning gas on, the system is pressure-tested with air or nitrogen using a gauge readable to small increments, with the test pressure and duration held for the code-specified period. Low-pressure residential systems are commonly tested at a minimum of 3 psi, with higher-pressure systems tested at a multiple of working pressure - always confirm the exact figure in 248 CMR 5.00 rather than relying on habit.
Rule of thumb
When a question asks why an added appliance starved the existing ones, the answer is usually longest length changed, not total BTU.