TL;DR
Make-up air is the outdoor air deliberately brought into a building to replace what exhaust fans, range hoods, dryers, and combustion appliances push out. Without it, a tight house goes negative, pulling flue gases down chimneys and radon or soil gas through the slab; IRC M1503 requires a powered system when a kitchen hood exceeds 400 cfm.
What it means
Make-up air is the outdoor air deliberately brought into a building to replace what exhaust fans, range hoods, dryers, and combustion appliances push out. Without it, a tight house goes negative, pulling flue gases down chimneys and radon or soil gas through the slab; IRC M1503 requires a powered system when a kitchen hood exceeds 400 cfm. HVAC contractors size the intake to the largest exhaust device and often interlock its damper with the hood.
Where it sits in the glossary
Make-up air is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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