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.