Combustion Air
Required combustion air opening from BTU input and room volume.
Example
You enter
- Appliance BTU input 100000
- Room volume (ft³) 4000
You get
- Required volume 5000 ft^3
- Outdoor opening 25 in^2
- Indoor opening 100 in^2
- Adequate by volume No (combustion air opening required)
Checked against published worked examples from: ICC.
Details, formula, and sources
Formula or tableRequired combustion-air opening per IFGC 2027 §304 (standard method): 1 sq inch per 4000 BTU/hr for outdoor air (two openings), and the larger 1 sq inch per 1000 BTU/hr for indoor communicating air.
Source and editionIFGC 2027 (International Fuel Gas Code) / NFPA 54. §304.
Free accessFree read-only access at codes.iccsafe.org.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field namesbtu_input, room_volume_ft3, required_volume_ft3, opening_outdoor_in2, opening_indoor_in2, adequate_by_volume
- Standard method IFGC §304.5; the known-air-infiltration-rate method (§304.5.2) is not applied unless user supplies; outdoor openings are §304.6IFGC 2027