Make-Up Air Unit

Equipment and Systems - Home Energy and Building Envelope pillar

Also known as: MUA, make up air, makeup air

A dedicated tempered air supply that balances large exhaust loads (range hoods, dryer vents, gas fireplace) in tight homes to prevent back-drafting.

When a kitchen range hood is over 400 CFM, it can pull more air out of a tight home than the envelope can passively replace, creating negative pressure that back-drafts gas water heaters and atmospheric furnaces. A make-up air unit is a powered fresh-air intake (often heated) that supplies replacement air whenever the exhaust fan runs. The Ontario Building Code and CSA B149.1 effectively require make-up air for any range hood over 400 CFM in homes with atmospheric-vented combustion appliances. Typical install: $1,500 to $3,500.

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