Bathroom and kitchen exhaust fans are meant to push warm, moist air outside through a duct to a roof or wall cap. A common shortcut, or a duct that has simply fallen off, lets them dump that air into the attic (or just recirculate it into the room), trapping moisture where no one looks.
$400 to $1,300 per fan to duct properly to the exterior (roof exits at the top end)Address soonInsulationInterior
The quick answer
Bathroom and kitchen fans are supposed to vent outside; a common shortcut dumps that moist air into the attic, where it condenses and grows mould and rot over a cold Canadian winter. It's cheap to fix and easy to verify, yet almost never noticed, about $400 to $1,300 per fan to duct it properly to the exterior. Run the fans and check where they actually exhaust.
You are reading the exhaust fans venting into the attic page. Type the year the house was built and I will tell you what else tends to be true at that age, what it costs, and what to ask. One number, ten seconds.
Free. No account. Educational and impartial, not a home inspection.
Why it matters
In a cold Canadian attic, all that bathroom humidity condenses on the underside of the roof sheathing and soaks the insulation, growing mould and rot over time and quietly degrading both the roof structure and indoor air quality. Building codes require these fans to vent to the exterior for exactly this reason, and Natural Resources Canada and CMHC both flag attic moisture from interior air leakage as a problem to control. It's cheap to fix and easy to verify, yet almost never noticed by buyers.
How to spot it
Run the fans and check where they actually exhaust: no cap visible on the roof or exterior wall; a flex duct lying loose or disconnected in the attic; a range hood that just blows back into the kitchen (recirculating); or damp, matted, or mouldy insulation and dark, stained sheathing above a bathroom.
What it costs
Roughly $400 to $1,300 per fan to duct it properly to the exterior with insulated duct and a proper cap, wall exits are cheaper, roof exits (attic access + roof penetration + weatherproof cap) sit at the top of the range; Toronto quotes for a quality fan vented through the roof run ~$1,300. First-time duct runs add $100 to $400.
What to do
Address soon. Have each fan vented to the outside with insulated duct and a backdraft-damper cap, and check the attic for moisture damage that may already have started.
Education and triage, not a home inspection. Casaroo flags improper venting from your fan and attic photos, easy and inexpensive to correct, and a contractor confirms.
Common questions
How do I check where the bathroom fan actually vents?
Run the fan and look for a cap on the roof or the exterior wall. If there is none, or if a flex duct is lying loose in the attic, the fan is dumping bathroom humidity into the attic. Correcting it runs about $400 to $1,300 per fan.
Is a recirculating range hood a defect?
It is not necessarily a code problem in every situation, but it does not remove moisture or combustion by-products from the house, it just filters and blows the air back at you. Worth knowing before you assume you have a vented kitchen.
What damage might already be done up there?
That is the real question. Warm, wet air in a cold Canadian attic condenses on the roof sheathing, soaks insulation, and grows mould and rot. Have the attic looked at, not just the fan.
Is this a negotiation item?
The fan itself is small money. Any attic moisture damage it has caused is not, and that is what you price. Get the attic assessed before you decide what to ask for.
Venting to the exterior is required by building code; a contractor confirms. Casaroo flags, it does not inspect.
Last reviewed 2026-07-10.
This guide is general education, not a home inspection and not advice for your specific property. Always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.