Damper Showdown - Control Dampers vs. Backdraft Dampers

Which would work better for an exhaust point: a control damper or a backdraft damper? Let's look at these two damper types and see which would work best.

The Scenario - HVAC Exhaust

You’ve just started an HVAC project and the plans call for airflow dampers at an exhaust point in the system. You need the damper to open for exhaust air and close when the cycle is finished. Two options come to mind. The first option is a standard control damper with an electric actuator. The second option is a backdraft damper. Which one works better for the situation? Let’s look at the pros and cons of each damper.

Control Dampers

Control dampers require an actuator to open and close their blades.

Control dampers open and close their blades with assistance from an actuator. Electric actuators can be tied to a control box, which allows an operator to open and close the damper remotely. Operators can also set the actuator to open at specific times, to synchronize with the system’s overall schedule. Control damper blades can be single-thickness, airfoil, or insulated airfoil blades. Insulated blades block heat when closed, preventing heat transfer from one side of the damper to the other. Insulation is important for systems that require precise temperature control.

You can also configure your control dampers to have parallel or opposing blade action, depending on the needs of the application. Read our article on blade action for the details. Each type of blade action has advantages, which add versatility to the damper. Control dampers are highly versatile, but their extra features can come at a cost. Certain accessories and options will increase the price of the unit. A control damper may have too many extra features for an exhaust application.

Backdraft Dampers

Backdraft dampers will open on their own when air passes through the duct in the intended direction.

Backdraft dampers are also built for air control. They open their blades when air flows through the duct in one direction, and close when air stops flowing. The blades stay closed if air passes in the opposite direction. Backdraft dampers are available with single-thickness or teardrop blades, which allow air through the damper with minimal resistance. They do not require an actuator to open. They use the force of airflow to open.

An optional counterweight can assist or resist the opening action, based on what you need the damper to do. Even with the counterweight option, the backdraft damper will be cheaper per unit than a control damper with an actuator.

The exhaust air will flow in one direction and backdraft dampers are designed for one-way flow. They can also work as a pressure relief damper, relieving pressure from the system as needed. You can save money by choosing the backdraft damper, assuming you don’t need it to do anything else.

Backdraft dampers only allow air through one way, which would work for an exhaust point. They remain closed if air tries passing through in the opposite direction.

Costs are always an important consideration, even after installation is complete. Control dampers will cost more over the life of the damper. You will need to purchase and maintain an actuator to operate the damper. Actuators require regular maintenance and will need to be replaced over the life of the damper.

Want to know more about actuators? Read more in "Actuators, Making Adjustments".

The actuator will be a key component of the damper and will need to be in full working order. If you only use the damper to open for exhaust air, then the costs will quickly outweigh the benefits. Backdraft dampers can open and close without an actuator, but they won't open for air flowing in the opposite direction. 

Pictured: A control damper allows airflow in both directions. The backdraft damper below will only allow airflow in one direction.

Which is better?

As you can see, each damper type has its advantages and disadvantages. Which one works best for the exhaust point? You know that the exhaust point won’t be used for intake. This means that a backdraft damper will work best.

The backdraft damper will open for the exhaust air without additional accessories. This saves you money and installation time. It also requires less work to maintain the damper, which saves the owner time and money. You should also consider where your project is located. If the building is in an area with a mild climate, then you won’t have to worry about cold or warm air seeping into the ventilation point.

In this situation, the backdraft damper is the most cost-effective option, and it performs the necessary task. Not all applications will be straightforward. A backdraft damper will not work if the ventilation opening requires two-way airflow. Choosing the right damper involves knowing more about your project. By understanding all the variables, you can make informed decisions.

For more on dampers, check out these articles on the Newsstand:

• Air Leakage - The Performance Killer
• Balanced Flow - Static and Dynamic Pressure
• Five Things to Know When Selecting Dampers
  

Starting a new HVAC project? Contact Arrow United Industries about our 517-518 steel control dampers. Let's work together on your next project.