Gas pipe sizing and the 2021 IFGC: what Denver contractors should know
Gas pipe sizing looks simple until a permit comes back for corrections or an appliance runs short on gas. This is a practical overview of how sizing works under the code Denver-area jurisdictions enforce, and where projects most often go wrong.
It starts with connected load
Every gas appliance has a BTU input rating from the manufacturer. Add them up and you have the total connected load the system has to deliver. That number, combined with the distance gas has to travel, drives every pipe size in the system. Get the load wrong and everything downstream is wrong.
Why distance matters as much as load
Under the IFGC (and the IRC fuel gas provisions, Section G2415), pipe is commonly sized using the longest run from the meter to the most remote appliance. Gas loses pressure over distance, so a long run to a high-demand appliance may need larger pipe than the load alone would suggest. This is the step where DIY diagrams most often fail: sizing for load but not for distance, leaving appliances starved at the far end of the system.
Same base code, local amendments
Colorado adopts the IFGC statewide, but jurisdictions amend it. Denver enforces the Denver Fuel Gas Code, based on the 2021 IFGC with Denver amendments; the gas piping provisions live in Chapter 4. Neighboring jurisdictions may enforce a different edition. A diagram has to be sized and stamped to the edition your reviewer uses, or it risks corrections.
What the PE stamp actually certifies
When a licensed mechanical engineer stamps a gas riser diagram, they're certifying that the sizing has been verified against the applicable code. That's what lets the building department accept it without re-deriving the calculations. It's also what protects you: correctly sized pipe means appliances that work and a system that passes inspection.
Skip the sizing headache
Send us your appliance list and plans. A licensed mechanical engineer will size and stamp your diagram, usually within two business days.
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