Kitchen Range Hood Venting: CFM Sizing, Make-Up Air Systems, and Exterior Ducting
A kitchen exhaust hood should move approximately 100 CFM for every 10,000 BTUs of gas cooktop output, or 250 to 400 CFM for electric/induction cooktops.
However, if you choose a high-performance hood rated at 400 CFM or higher, North Carolina building code (NCRC Section M1503.6) legally mandates the installation of an automatic make-up air system. Exhausting 400+ CFM from a modern, tightly sealed home creates dangerous negative air pressure that can backdraft carbon monoxide from gas water heaters and fireplaces.
Why Make-Up Air Systems Are Code-Mandated
When a 600 or 900 CFM range hood operates on high, it exhausts large volumes of conditioned air. In tight homes, replacement air cannot leak through windows, so furnace and water heater flues become the path of least resistance, drawing toxic exhaust backward into living areas.
A code-compliant make-up air system utilizes a motorized damper synchronized with the hood switch to draw fresh, filtered exterior air into the home or HVAC return.
Duct Material and Termination Standards
Range hoods must exhaust outdoors through smooth-walled rigid galvanized steel or copper ducting (NCRC Section M1503.2). Flexible foil or ribbed ducts are prohibited because grease accumulates in corrugations, creating an intense fire hazard. Ducts must terminate outdoors with backdraft dampers, never in attics or soffits.
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