Chimney-style range hood with a glass canopy over a cooktop
Generic photo: Bilguun Gantumur · Pexels License

Range hood over 400 CFM: does the job need makeup air? (IRC M1503.6 check before you sell the hood)

Under the IRC kitchen makeup-air section (M1503.6 in recent editions, M1503.4 in 2009), a hood able to exhaust more than 400 CFM needs makeup air at roughly the same rate, with at least one damper that is gravity or motorized and opens automatically when the hood runs. Recent editions apply it only when the home has a fuel-burning appliance inside the air barrier that is neither direct-vent nor mechanically drafted (e.g., a natural-draft water heater or a wood fireplace). States and cities amend this, so the local code office decides. This guide is a pre-sale and diagnosis check, not an HVAC design.

Cross-checked ~30 min moderateBrands: All

Before you start

  • A big hood can backdraft a natural-draft water heater, furnace or fireplace and pull combustion gases (including CO) into the house; if you see spillage or the CO monitor alarms, shut the hood off, ventilate and refer to a licensed HVAC/gas tech
  • Do not adjust or modify gas appliance venting; that is licensed work
  • Makeup-air ducts, dampers and interlocks are usually HVAC/electrical work and may need a permit

Diagnostic steps

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Range hood over 400 CFM: does the job need makeup air? (IRC M1503.6 check before you sell the hood) · OnCall Tech