Backdraft & Pressure Relief Dampers - Backdraft - Selection and Series Overview

Oct 22, 2026

Backdraft dampers and relief dampers support ventilation systems by permitting airflow in one direction while preventing reverse flow. The catalog outlines selection criteria including system velocity, back pressure, mounting orientation, mounting configuration, damper operation type, and start-open pressure. It explains frame construction options, spring and motor-assisted opening mechanisms, and provides performance guidance and series ranges for BD, WD, GM, and EM models. It also includes application examples, airflow orientation variants, and model-specific start-open pressure and leakage performance details, plus optional end switch kits for open/closed indication.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages16

Reading Time40 min

AccessFree to download

Backdraft & Pressure Relief Dampers

Backdraft

Selection Information

Mounting Orientation

Frame Construction

Commercial Backdraft Dampers

Damper Operation and Opening Assist

Damper Series Ranges and Applications

BD Series

BD-300 Series (Model Table)

WD Series

WD-100 to WD-400 Series

Round Models (WDR-53/SSWDR-53)

End Switch Kits

Backdraft & Pressure Relief Dampers • Backdraft • Barometric Relief • Pressure Relief March 2023 Backdraft Dampers Backdraft dampers (also known as gravity dampers) are used in ventilation systems to allow airflow in one direction and prevent airflow in the opposite direction. A relief damper is developed with an elevated and adjustable start-open pressure while providing the backdraft function. The following information is needed when selecting the proper damper application: • System velocity and back pressure requirements • Mounting orientation and airflow direction • Mounting configuration (inserted into duct/opening or flange-mounted) • Damper operation (gravity or motorized) • Start-open pressure Mounting Orientation Backdraft dampers are available in vertical or horizontal mount. Horizontal Mount Airﬂow Up Horizontal Mount Airﬂow Down Frame Construction Three types of frame construction are available on all commercial backdraft damper models: • No flange • Flange on discharge • Flange on intake Duct Duct No Flange (Duct Insert) Flange On Discharge Flange On Intake Commercial Backdraft Dampers A commercial backdraft damper is a gravity damper (when nonmotorized) that allows airflow in one direction only. When placed on a propeller fan, for example, it will prevent the wind from causing the fan to run backwards when the power is off. A motorized backdraft damper functions like a control damper. To assist with opening the damper blades, backdraft dampers may utilize springs, adjustable counterbalance weights, or a motorpack. • Spring assist is a spring attached to the damper that helps in opening or closing the damper blades. The spring is adjustable by using a series of holes in the frame or blade assembly to increase or decrease the tension. • Adjustable counterbalance weights are a more precise means of reducing the pressure that is required to open the damper. • A motorpack is used when it is necessary that the damper opens and closes without having to rely on air velocity or pressure. Backdraft damper selection begins by determining the damper construction required based on system velocity and static pressure. The BD damper series is used in applications up to 1500 ft/min (7 m/s) and 2 in. wg (0.5 kPa) of static pressure. The WD and GM damper series are used in applications up to 2500 ft/min (12.7 m/s) and 2 in. wg (0.5 kPa) of static pressure. The EM damper series is used in applications up to 3500 ft/min (17.8 m/s) and 10 in. wg (2 .5 kPa) of static pressure. BD, EM, GM, and WD series dampers can be used in applications for: • Exhaust • Roof ventilation • In-duct ventilation • Air intake • Sidewall ventilation BD Series BD series have a galvanized steel frame with aluminum blades. The dampers are opened by air pressure differential and closed by gravity. They are rated for velocities up to 1500 fpm (7 m/s) and pressures up to 2 in. wg (0.5 kPa) . These dampers have AMCA certified pressure drop and leakage performance that comply with ASHRAE 90.1 and IECC leakage requirements for nonmotorized dampers. BD-300 Series | Model | Flange | Mounting
Position | Airflow
Direction | Spring
Assisted | Maximum
Velocity
fpm (m/s) | Start Open
Pressure*
in. wg (kPa) | Maximum
Back Pressure
in. wg (kPa) | AMCA Air
Leakage & Air
Performance | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | BD-100 | None | H | Vertical
Up | Std | 1500
(7) | 0.01
(0.002) | 2
(0.5) | Yes | | BD-300 | Intake | V | H | N/A | 1500
(7) | 0.009
(0.002) | 2
(0.5) | Yes | | BD-320 | Discharge | V | H | N/A | 1500
(7) | 0.009
(0.002) | 2
(0.5) | Yes | | BD-330 | None | V | H | N/A | 1500
(7) | 0.009
(0.002) | 2
(0.5) | Yes | H = Horizontal V = Vertical N/A = Not Available Std = Standard *Start-open is the pressure at which the damper blades begin to rotate. The blades are not fully open at this po

FAQs

What is the purpose of backdraft dampers in ventilation systems?

Backdraft dampers allow airflow in one direction while preventing airflow in the opposite direction. They help stop reverse wind from running a fan backward when power is off.

How do you select the correct backdraft damper for an application?

Selection starts with required system velocity and static pressure, plus mounting orientation and airflow direction, mounting configuration, operation method (gravity or motorized), and the required start-open pressure.

What opening-assist options are used for backdraft dampers?

Backdraft dampers may use springs, adjustable counterbalance weights, or a motorpack. Springs can be adjusted via holes to change tension, while counterbalance weights reduce the opening pressure more precisely.

What do BD and WD damper series support in terms of velocity and pressure?

BD series are used up to 1500 ft/min and 2 in. wg static pressure, while WD and GM cover up to 2500 ft/min and 2 in. wg. EM series extend up to 3500 ft/min and 10 in. wg. WD variants include motorized and nonmotorized options for different mount and airflow scenarios.

Oct 22, 2026

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