How Does a Backdraft Damper Work

How Does a Backdraft Damper Work?

Backdraft dampers are often the unsung heroes of HVAC systems that ensure air flows in the way it was intended. If you're involved in HVAC, ventilation, or even home maintenance, understanding the function of a backdraft damper is crucial. Energy efficiency, indoor air quality, and proper HVAC system operation all rely on backdraft dampers doing their part. In this article, we'll delve into the mechanics, applications, and benefits of backdraft dampers.

How Does a Backdraft Damper Work

Image Source

What is a Backdraft Damper?

A backdraft damper is a device installed in ventilation systems to control the flow of air. It is designed to allow air to flow in one direction only, and prevent it from flowing backward or "back drafting." Similar to a check valve in plumbing or pneumatics, backdraft dampers are essential in managing airflow, reducing energy costs, and maintaining indoor air quality inside a building.

How Does a Backdraft Damper Work?

Backdraft dampers exist in many different configurations but all accomplish the same basic functions.

Basic Mechanics

A backdraft damper typically consists of a set of blades or flaps that are mounted inside a duct or fan housing. The blades are designed to open when there is a positive airflow in the intended direction. When the airflow stops or reverses, the blades automatically close, thereby preventing backdraft. Sometimes the closing action happens simply via gravity and other times an outside force like a spring is used to pull the backdraft damper shut.

Material and Design

Backdraft dampers are commonly made of either metal or plastic, depending on the application and environmental conditions. The blades of the backdraft damper typically have an axle that runs through one end of the board to allow the flap to pivot and open. Oftentimes a counterbalance is used to reduce the amount of force required to open the backdraft damper.

Types of Backdraft Dampers

Backdraft dampers are used in many different environments and applications, so there are different types in order to fulfill various needs.

Gravity Operated

These rely on the force of gravity to open and close the blades. They are often simpler and less expensive, but may not be as efficient in high-pressure systems.

Gravity-operated backdraft dampers must be properly installed to ensure they will be able to open and close as designed.


These dampers use a spring mechanism to quickly shut the blades when the airflow reverses. They are more reliable in high-pressure systems but may be more expensive.

Spring-loaded backdraft dampers have more complex mechanisms and may require periodic maintenance to ensure they continue to function as designed.


These are electronically controlled and offer the most precise control over airflow. They are often used in complex HVAC systems. While motorized backdraft dampers offer the highest level of control, these dampers also have the greatest maintenance requirements and can be more difficult to service due to the controls involved.

Applications of Backdraft Dampers

Any HVAC system is a likely candidate for a backdraft damper application. Here are some of the most common applications for backdraft dampers:

Kitchen Exhaust

A backdraft damper in a kitchen hood exhaust will prevent odors and smoke from re-entering your home or building. Backdraft dampers also help prevent unconditioned air from entering the kitchen when the exhaust fan is off.

Bathroom Fans

Just like kitchen hood exhausts, bathroom exhaust fans make good use of backdraft dampers. Backdraft dampers can prevent humid air from flowing back into your bathroom, to help reduce the chance of mold growth and to help ensure that odors are properly exhausted. These dampers also prevent unconditioned air from entering the building when exhaust fans are not running.

HVAC Systems

In large buildings, backdraft dampers are essential for maintaining energy efficiency and air quality. They help prevent air from traveling in unwanted ways. For large HVAC systems that rely on multiple supply fans in parallel configurations, backdraft dampers are used to automatically remove a broken fan from service. If a supply fan does not operate correctly, the backdraft damper allows the system to continue to operate until repairs can be made.

Industrial Exhausts

In factories, dampers can prevent harmful fumes from re-entering the workspace. Keeping air moving properly keeps people safe and can keep product or machines under the correct operating conditions.

Clean Rooms

In environments where air purity is essential, backdraft dampers are used to maintain positive pressure. Without backdraft dampers, air could flow from an unclean section into the clean room section, which could contaminate the room.

Benefits of Using a Backdraft Damper

Backdraft dampers provide a host of benefits including:

  • Energy efficiency
  • Improved air quality
  • Durability and redundancy

By preventing conditioned air from escaping, backdraft dampers can significantly reduce energy costs. They also help in maintaining indoor air quality by preventing the re-entry of polluted air or high-humidity air. Modern backdraft dampers are built to last and require minimal maintenance while allowing units a degree of redundancy to operate even when a failure occurs.

United Enertech: Backdraft Damper Specialists

United Enertech has provided the industry with more than thirty years of quality products and reliable service. Their expertise covers all types of air control devices, including backdraft dampers. Some of their most popular backdraft dampers include:


Best for light-duty commercial applications, the CB-600 Damper offers reliable performance at an affordable price. Suitable for airflows up to 2,800 fpm, these dampers are easy to install in ventilation systems to ensure airflow moves in only one direction.

Model CD

Ideal for commercial HVAC systems, the Model CD gives contractors an easy balance damper option. Often used in heat pump relief and bypass, these dampers are easily adjustable and simple to maintain. The Model CD damper offers quick and reliable performance.


For the most demanding applications, the I-900 is unmatched. Designed for applications up to 10” wg, the I-900 is an industrial backdraft damper with a heavy-duty flanged frame style. These backdraft dampers are tough and reliable. For specialty industrial applications, this is the go-to product.

United Enertech: A Leader in Air Control Products

Understanding how a backdraft damper works is the first step in optimizing your ventilation system for both efficiency and safety. From residential kitchens to industrial exhaust systems, the applications are endless.

If you're ready to make a change for the better, check out United Enertech's range of backdraft dampers. Designed with performance and durability in mind, United Enertech has a product for every need. Reach out to the backdraft experts at United Enertech today and breathe easier knowing that you've made a smart choice!