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What is a Duct Damper?

By B. Turner
Updated May 17, 2024
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A duct damper is a device used within a heating, ventilation and air conditioning (HVAC) duct. These ducts carry air from furnace or air conditioning units to the different rooms within the building. A duct damper can help control the flow of this air, or can even prevent the air from entering specified areas. By regulating air flow, the duct damper can be used to control temperature and humidity levels, restrict the flow of dangerous fumes or smoke, or simply give homeowners more control over comfort levels and drafts.

These dampers can take a number of different forms depending on the desired function. A duct damper may contain a rotating flapper-type mechanism, which will pivot back and forth within the duct to control air flow. It may also contain a louver or vent-type mechanism, which can slow or redirect air flow, but is ineffective at blocking airflow completely. Finally, guillotine dampers are designed to block the entire duct so that air is unable to enter a specific area.

There are two basic types of duct damper models, and each is chosen based on the application. Volume air dampers control overall air flow as part of the building's heating and cooling system. As the thermostat is adjusted, the dampers automatically activate to increase or decrease air flow. They can also be used to redirect conditioned air out of closed-off rooms, which prevents wasted energy and keeps utility bills in check.

Fire or smoke dampers are typically used only at fire-rated partitions, or at ceilings and floors that act as a fire break between two areas. They are designed to prevent the spread of smoke or flames through the building's ductwork. Many contain integral smoke detectors that activate the air damper when smoke is present. Others have a fusible link-type element, which melts to shut the damper once temperatures reach a certain level.

Most dampers are also available with a manual operating option. They typically operate using a crank or switch located on the outside of the duct. Users must turn this crank to open or close the damper for both volume control and smoke control. While this option is simple and affordable, it may be impractical in emergency situations, when operators must activate the duct before exiting the building.

Mechanical engineers and builders select duct dampers to fit the surrounding ductwork. The damper must have the same shape as the duct, and may be round, square or rectangular. Each damper must fit precisely within the duct to prevent air leaks and ensure the damper will function as intended.

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Discussion Comments

By Drentel — On Feb 01, 2014

Sporkasia - Closing and opening the manual or motorized duct damper to control heating to particular rooms or areas of your house works best when the rooms are well contained. In other words, if there are big gaps below or above doors this method will not work as well. Sure, it might make a difference, but your heating bills won't drop too much.

By Sporkasia — On Jan 31, 2014

We live in an old two story house that has way too much square footage, much more than we actually need or use. We close and open the duct dampers depending on how much heat or air we want to let into a particular area of the house.

The first winter we owned the house we didn't do this the first cold month and our heating bill was very high. Once we started using the heating duct dampers our heating cost went back to a reasonable figure. You wouldn't think closing off a few rectangular duck dampers would make a significant difference, but it does.

By Drentel — On Jan 30, 2014

I worked in a building once that had the automatic dampers. Their primary function was to close off and keep smoke or gases from spreading through the duct work during a fire or gas release, but they were also used to control temperatures in various parts of the building.

Some units in the building had to be very cool because they were used to store chemicals that needed to stay below a certain temperature so they wouldn't become dangerous. One of the engineers showed me how the system worked and it was pretty intricate and cool.

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