Combustion air is the oxygen-containing air required for the chemical reaction that burns fuel in furnaces, boilers, and water heaters. A typical gas burner requires approximately 17 to 20 cubic feet of air for every cubic foot of natural gas burned. Proper combustion air supply is critical for safe, efficient operation and compliance with building codes.
Air Supply Requirements
Combustion air can come from three sources: direct room air in naturally drafted systems, dedicated outside air ducts in sealed combustion systems, or a combination approach. Furnaces typically require 50 to 100 CFM of combustion air depending on fuel input rating. Air must be free of dust, lint, and obstructions that reduce oxygen availability.
Code Compliance and Safety
The International Fuel Gas Code mandates that combustion air be supplied from outdoors or from an unrestricted space with adequate volume. Inadequate air supply causes incomplete combustion, producing dangerous carbon monoxide at concentrations exceeding 400 ppm. Sealed combustion systems offer superior safety by drawing outside air directly through dedicated pipes, preventing indoor air depletion and back-drafting hazards.