Non Return Dampers

Frequently asked questions

What is a backdraft damper?

A backdraft damper is a one-way valve for air. Its blades are pushed open by the airflow when the fan runs and close under their own weight or a light spring when the fan stops, so air cannot flow back down the duct. It stops cold draughts and heat loss through an idle extract duct, keeps out wind-driven rain and insects, and prevents air from one fan being pushed back through another outlet in a shared system.

Non return damper, backdraft damper or backdraught shutter: are they the same?

Broadly, yes. Non return damper and backdraft damper usually mean an in-duct damper that fits inside a circular duct run. Backdraught shutter usually means a louvred shutter on the outside face of a wall or the outlet of a fan or roof cowl. All of them do the same job of letting air out and stopping it coming back.

Which type do I need?

Fit the in-duct back draught damper where you want the protection inside the duct, for example close to an inline fan or on a duct that joins a shared riser. It comes in circular sizes from 100mm to 315mm. Fit the VK gravity louvre shutter on the outside wall over the end of an extract duct or a wall-mounted fan. Fit a BDS shutter on a Systemair RAW roof cowl to stop air and weather coming down a roof extract when the fan is off.

Can a backdraft damper be fitted vertically?

The Systemair back draught damper has spring-loaded blades, so it closes reliably in vertical and horizontal ducts. Gravity shutters such as the VK rely on the weight of the vanes to close and must be mounted vertically on a wall. On a vertical riser, make sure the damper opens in the direction of the airflow.

Will a backdraft damper reduce my fan's airflow?

Slightly. The fan has to push the blades open, which adds a small amount of resistance. The VK shutter's profiled vanes open fully at low air velocity, which keeps the loss small, but on a small fan with a long duct run it is worth allowing for. Very small domestic fans sometimes cannot open a heavy shutter fully, so match the damper to the fan.

Do I need a backdraft damper on a bathroom or kitchen extract?

It is good practice on any extract that runs intermittently. Without one, an idle duct lets cold air and draughts back into the room and can cause condensation in the duct. Many bathroom fans have a shutter built in. If yours does not, or the duct runs through a cold loft, add a non return damper in the run or a shutter on the outlet.

Is a backdraft damper a fire damper?

No. A backdraft damper only stops reverse airflow. It has no fire rating and must never be used where a duct passes through a fire compartment wall or floor. That needs a tested fire damper, see our fire dampers.

Do you supply dampers for trade and project work?

Yes. We supply M&E contractors, ventilation installers and facilities teams, with stock on the Systemair range for next day delivery. Send a schedule and we will match dampers and shutters to the duct and fan sizes. Call 0161 399 3825 or email hello@efans.co.uk.