Galvanized Round Backdraft Damper
The damper that lets air out and stops it from coming back, keeping cold outdoor air out of the house.
AirGreen codeAG-VC-01604
514 316-2973 · sales@airgreen.ca
Quick facts
The galvanized round backdraft damper installs in an exhaust duct. It opens when the fan pushes air outside and closes as soon as the air stops. Its job: keep cold air, wind and odours from coming back down the duct and into the house.
Cold coming back through the bathroom fan
A cold draft under the bathroom fan, frost in the duct, odours moving from one room to another: these symptoms often come from an exhaust duct with no backdraft protection. The flap on the wall cap closes the outlet at the wall; the in-line damper adds a barrier inside, useful on wind-exposed walls and on systems where several ducts join the same fan.
Four diameters
Available in 4, 5, 6 and 8 in. Choose the nominal diameter of the exhaust duct, usually that of the fan collar.
Installing it properly
- Respect the direction of flow: the blade opens toward the outlet.
- Check that the blade moves freely; a screw that is too long can jam it.
- Seal the joints with aluminum tape or mastic, and insulate the duct in an attic.
- Give the duct a slight slope toward the outside so condensation drains out.
Installed by AirGreen across Greater Montréal
We install exhaust ducts, dampers and wall caps in Montréal, Laval, Longueuil, on the South Shore and on the North Shore. RBQ licence 5645-9605-01, subcategory 15.8 Ventilation. For availability or a quote, call us at 514 316-2973 or email sales@airgreen.ca with the diameter and quantity.
Shutting the door on wind and cold
When a fan stops, outdoor air tries to come back down the duct: the backdraft damper closes and blocks it.
- Bathroom fan exhaust duct
- In-line fan serving one or more rooms
- Branches joined toward one fan, to keep air from passing from room to room
- Ducts where wind makes the wall-hood flap rattle
4 sizes, one page
Each size has its own AirGreen code. Tap a row to select it.
Nominal round duct diameter.
Specifications
From the manufacturer’s documentation. A value the manufacturer does not publish is not listed.
What to know before installing
- Follow the airflow direction: installed backwards, the damper blocks the air instead of letting it through.
- Check that the blade moves freely once installed, without rubbing on a screw.
- Keep it reachable for inspection and cleaning.
- Seal both joints with foil tape or mastic.
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Frequently asked questions
What does a backdraft damper do?
It stops air from flowing backwards in an exhaust duct: cold outdoor air, odours or air from another room while the fan is off.
The wall hood already has a damper; do I need another?
The hood’s damper closes the outlet at the wall. An in-line damper adds a second barrier, useful on wind-exposed exhaust or where several ducts join.
How do I know which way to install it?
The blade must open in the direction the air leaves. Dry-fit the damper and check the movement before screwing it.
Can you install it?
Yes. We install exhaust ducts, dampers and wall hoods across Greater Montréal.
Exhaust that keeps the cold out
Tell us the size and the quantity: we confirm availability and send you a quote. Or let our technicians install it for you.
Specifications from the manufacturer’s documentation, checked on October 7, 2026.