What Is a Backdraft Damper? Specs and How to Specify One
A backdraft damper opens with airflow and closes automatically under gravity or spring tension to stop reverse flow, without needing power or a control signal. Specs, applications, and how to specify one.
A backdraft damper is an HVAC damper that opens when air flows through it in the intended direction and closes automatically under gravity or spring tension when that flow stops, preventing air from moving backward through the duct. Goodwind manufactures the Backdraft Damper (model GT-BKD) in aluminum, galvanized steel, or stainless steel, sized to the duct dimensions, as part of its wider damper range designed to minimize turbulence and noise.
Backdraft Damper Specifications
| Spec | Detail |
|---|---|
| Model | GT-BKD |
| Material | Aluminum, galvanized steel, or stainless steel |
| Size | Customizable to duct dimensions |
| Operation | Passive — opens with forward airflow, closes automatically under gravity or spring tension |
| Applications | Exhaust fan backflow prevention, parallel fan installations, HVAC airflow regulation |
Backdraft Damper vs. Volume Control Damper
Both sit inside a duct run, but they do different jobs. A volume control damper is manually or automatically positioned to regulate how much air passes through, and stays wherever it's set. A backdraft damper has no set position at all — it's fully passive, opening only when air pushes through it in the correct direction and closing on its own the moment that airflow stops, with no motor, control signal, or manual input needed.
How to Specify a Backdraft Damper
For MEP Consultants at the Design Stage
Where Backdraft Dampers Are Actually Needed
Specify a backdraft damper wherever reverse airflow is a real risk — most commonly on exhaust fan discharges, or where multiple fans exhaust into a shared duct or louver and an idle fan could otherwise let outside air or another fan's exhaust flow backward through it.
Choosing Gravity vs. Spring-Assisted Operation
A gravity-operated damper relies on blade weight alone to close, which works well for horizontal duct runs but can be too slow or unreliable in a vertical run. A spring-assisted damper closes faster and more positively regardless of orientation, which matters more as the risk or cost of reverse airflow increases.
For Contractors at Procurement Stage
Confirming Orientation Before Installation
Confirm the intended airflow direction and duct orientation (horizontal or vertical) against the drawing before ordering, since a gravity-operated damper installed in the wrong orientation may not close reliably.
Verifying Material Against Site Conditions
Match the material to the environment — stainless steel where the airstream carries moisture or corrosive elements, galvanized steel or aluminum for standard indoor applications — rather than defaulting to whatever's on hand.
FAQ
What is a backdraft damper used for?
It's used to prevent reverse airflow through a duct, most commonly on exhaust fan discharges or where multiple fans share a common duct or louver.
Does a backdraft damper need power or a control signal?
No, it's fully passive — it opens with forward airflow and closes automatically under gravity or spring tension when that flow stops.
How is it different from a volume control damper?
A volume control damper is set to a fixed position to regulate airflow volume. A backdraft damper has no set position — it opens and closes entirely on its own based on airflow direction.
What materials are backdraft dampers made from?
Aluminum, galvanized steel, or stainless steel, sized to the duct dimensions.
Worried about reverse airflow in a shared exhaust run? Contact Goodwind for technical input, or see our volume control damper guide for everyday airflow regulation.