/ Field knowledge · IMC 701
If it can fire with the damper closed, the design is wrong.
IMC 701: a grille on the plan is not combustion air. If the appliance can fire while a required damper is closed, the design has a safety problem.
Educational 2024 IMC 701 (Daily Code Talk: scope and dampered openings). Confirm adopted edition and the fuel-gas path. Gas-fired appliances are not reviewed the same way as oil-fired or solid-fuel. Direct-vent appliances, fireplaces, and fireplace stoves need careful scope handling. Distinct from the general combustion-air hub. This page does not size openings.
- Select the right path first: mechanical code, fuel gas code, oil-fired standard, solid-fuel manufacturer instructions, or another listed installation path.
- Prove the air path is available: product free area, screen losses, louver data, duct routing, room pressure, and appliance startup logic. Nominal dimensions are not free area.
- Highest-risk detail: a dampered combustion-air opening. The control sequence should prove the opening before the appliance is allowed to operate.
- Coordinate any combustion-air duct crossing rated construction with the building-code protection path. Check whether exhaust systems can depressurize the appliance room during worst-case operation.
Startup should verify combustion air with the building in the operating mode that creates the greatest negative pressure. The reviewer needs the appliance, the air source, the opening-size basis, the duct or rated-construction route, and the controls logic — not a note.
Damper closed, burner on
If the drawings cannot answer “can the appliance prove it has combustion air before it fires?”, there is safety, startup, and inspection risk. Escalate tight rooms, large exhaust, rated shafts, oil/solid-fuel, or manufacturer instructions more restrictive than the assumed path.
Source: DCT 701 · tool: damper screen · hub: combustion air.
What to send
The appliance fuel/input, whether a damper is in the CA path, and whether a proof-of-open interlock is shown.
If the CA opening has a damper
Send the sequence. Masterbuild will say whether 701 even proves the opening before fire — or the appliance can run against a closed path.
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. Confirm the adopted edition. Field observations do not establish electrical safety; only qualified personnel using required safe-work procedures should access electrical equipment.