/ Hub · IMC Chapter 7 · Combustion air
Combustion air needs a proof chain, not a louver guessed on the elevation.
Fuel-fired appliances fail at the air-supply path as often as they fail at the flue. IMC Chapter 7 is the drawing: appliance, method, free area, damper interlock, and what happens in an existing room that was never sized for the replacement unit. Dampered openings: IMC 701 proof-of-open.
Open the combustion-air method check
What the drawings should identify
- Appliance type, fuel, and whether it is indoor, outdoor, or direct-vent
- Combustion-air method: indoor volume, outdoor openings, ducts, or engineered
- Opening size as free area — not nominal louver size
- Dampered openings that interlock with the appliance, not gravity “hope”
- Rated-assembly penetrations and coastal / HVHZ opening protection
- Existing-room constraints when a larger or tighter appliance replaces the original
Replacement unit, original closet
Sealed-combustion marketing copy does not automatically retire Chapter 7. Confirm the listing and the actual air path before the closet is framed.
Louver free area ignored
A 12×12 louver is not 144 in² of free area. The grille, screen, and damper eat the opening. Plan review will ask.
Daily Code Talk
- IMC 701 combustion air — scope and dampered openings
- IMC chapter map · Chapter 7 Combustion Air Field Guide
What to send
Appliance cut sheets, mechanical-room or closet dimensions, existing opening locations, and whether this is new construction or a replacement in a sealed room.
Send the appliance and the room
Cut sheets plus the closet or mechanical-room dimensions. That is enough to start a written scope.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval.