Dampers control the direction and volume of airflow within a duct to maintain a balanced HVAC system. Most systems use dampers in some form to control airflow — they operate as doors (either manually or automatically) that allow, redirect, diffuse or stop airflow.
Homeowners should know about the various types of HVAC system dampers as they’re critical to energy efficiency and fire protection. Keep reading to learn more about the common damper types in HVAC applications and how they help your system operate.
Common Types of HVAC Dampers
Most residential and light commercial HVAC systems incorporate different types of dampers to achieve a balanced system. These types include radial, rectangular, round-tube, collar-tube, shutter and blade-style dampers. Industrial applications may require custom-designed dampers, but they generally perform the same functions.
While all dampers stop, limit, or redirect airflow, each design offers specific benefits such as better sealing, one-way operation and precise airflow control. Most dampers are made from galvanized steel, but other materials, including aluminum and stainless steel, are used depending on the application.
Blade-style (also known as collar-type) dampers use either a single rotating blade or several long blades that work together to control airflow. Most blade-style dampers are round, square, or rectangular and are usually located near a junction in the system to isolate a zone or area.
Guillotine-style dampers are often used when a system requires the best seal. They usually have a gasket that glides against the blades as it closes and creates an airtight seal. Guillotine dampers close very quickly and are useful in emergencies, like quickly preventing the spread of fire by denying it air.
Shutter-style dampers allow for automatic airflow in only one direction. These dampers prevent air from moving back through the unit. Backdraft dampers are shutter-style dampers commonly found on fans to prevent back pressure.
Radial-style dampers use more than one rotating blade to provide very precise airflow control. These dampers open like a fanned-out deck of playing cards, allowing the designer to precisely diffuse and control airflow. Radial-style dampers have openings and notches in specific locations on the blades to maximize efficiency and effectiveness.
Rectangular-style dampers usually use flat blades that pivot around a center hub. In an HVAC system, you may find a rectangular damper in the form of a floor or wall register. Often, a slider is used to open or close the damper’s blade to control airflow into a room.
Round tube dampers are usually longer than normal collar-style dampers and are often self-contained units. Round tube-style dampers will generally replace a short section of flexible ductwork with a short, rigid section (less than 24 inches) and contain the damper and controls. Round tube-style dampers are commonly inserted as needed after the system is operational.
Manual vs. Automatic Operation
Dampers can be operated manually or automatically, depending on the application and purpose. Most residential systems use manually operated blade-style dampers. Usually, contractors adjust and set the blades during initial installation, and they can be changed in the future.
Other HVAC systems require greater control and may include plenum spaces necessitating airflow restrictions. Often, dampers in these systems are automatically adjusted based on temperature and volume presets and are controlled by the system and a thermostat. Radial-style dampers are common in these circumstances due to their greater control capabilities.
Most HVAC dampers are the blade type, located inside a collar within the ductwork. The blade, which is slightly smaller than the diameter of the duct, spins like a revolving door. The locking adjustment handle extends outside the duct, allowing the installer to restrict or allow airflow as needed. In most systems, if the handle is parallel to the duct, the damper is fully open.
Some dampers may need to be adjusted periodically. Often, they’re manually controlled via a cable system. Mechanical actuators that open and close the damper are controlled with these cable systems, which are highly reliable and rarely need maintenance.
Sometimes, design requirements place ductwork in less-than-ideal locations, meaning adjusting dampers requires moving or uninstalling other components. In these cases, mechanical actuators are extremely useful because they save time and effort.
Some dampers are controlled automatically by electrical switches and actuators. Automatic dampers are used in complex HVAC designs requiring multiple controls to create a balanced system. Automatic dampers are also common in locations such as very low attic spaces that are difficult to access.
As a solution to manual dampers that need periodic adjustment, some newer HVAC damper designs incorporate wireless technology. Each damper is fitted with a wireless receiver and transmitter and is controlled remotely. Wireless dampers can be retrofitted to replace manual dampers that are a hassle to access.
Uses of Dampers In HVAC Systems
Control dampers are used to stop, allow, or mix airflow through adjustment of the rotating blades. They’re are often controlled by a thermostat or remote. In most configurations, a control damper is designed to open and close automatically to control air volume and pressure.
Balancing dampers, like control dampers, open and close multiple blades to restrict airflow. These are usually used between two adjoining spaces where one is receiving more air pressure than the other.
Balancing dampers are typically set by the installer and permanently locked into position but can be readjusted.
Balancing vs. Control Damper
Control dampers and balancing dampers are easily confused with each other because they look similar and perform a similar function. Knowing the difference is important because they’re not necessarily interchangeable.
Balancing Dampers Have Parallel Blades
Balancing dampers are designed to impede airflow on one side of the damper and increase it on the other. They typically have three or four parallel blades that all move in the same direction at the same time. Most balancing damper blades rotate around a center pin and can be rotated almost 180 degrees in either direction.
Control Dampers Have Opposing Blades
Control dampers are opposing blade dampers. Each blade rotates in the opposite direction of the blade next to it, which applies pressure against the seal from both directions. In contrast to balancing dampers, control dampers will either be fully open or fully closed.
Other Types of Dampers
Backdraft dampers are common in homes, even beyond your HVAC system. They allow air travel in one direction only, so they’re used in bathroom vent fans, range hoods, and dryer vents. Backdraft dampers allow exhaust air to exit the home while outside air pressure prevents reverse airflow.
Butterfly Damper
Industrial HVAC systems sometimes require complex airflow control because the structures are so large. Heated air traveling long distances through ductwork may cool off before it reaches its destination.
Butterfly dampers are commonly used in industrial applications to provide more control over air leakage and flow to solve this problem. They use a flat, circular metal blade and work best in round ducts.
Inlet Vane Damper
Inlet vane dampers are commonly used in industrial applications, usually near the air intake. In most applications, inlet vane dampers are used to precisely control airflow and air pressure from the inlet side of the blower fan. Inlet vane dampers are unique in that the angle of attack from the blades is adjustable.
Just like the blades on a helicopter, the blades on an inlet vane damper can be pivoted in place to allow more or less airflow. Inlet vane dampers are usually round and are available in both residential and industrial versions.
Multi-zone dampers are electrically controlled dampers that can be either programmed to a particular state or adjusted as needed by the system. Many HVAC systems are divided into control zones, which are usually rooms that have their own ductwork.
Each HVAC zone will be controllable and programmable, providing more consistent airflow and air pressure. Multi-zone HVAC dampers can be used in conjunction with other dampers, such as backdraft and control dampers, to establish the most efficient airflow path. Multi-zone dampers are often controlled continuously by the system and the thermostat.
Dampers In Your HVAC
Dampers control and regulate airflow within HVAC systems. They adjust the volume of air flowing through ducts to different areas of a building. Dampers also work to maintain temperatures in zones within a structure and allow for targeted heating and cooling. They help maintain energy efficiency, balance air distribution and control ventilation, reduce noise transmission through ductwork and manage air pressure in HVAC systems. Some dampers prevent fires from spreading through ducts.
FAQs About Dampers
What's the purpose of a damper?
Dampers control and regulate airflow within HVAC systems by managing the volume of air flowing through ducts to different areas of a building. They also help maintain desired temperatures in specific areas, improve energy efficiency, and curb the spread of fire through your duct system.
By serving these functions, dampers play a crucial role in the overall efficiency, effectiveness, and safety of HVAC systems. They provide a way to fine-tune the system’s performance to meet specific comfort and energy-saving needs throughout the year.
Can I install dampers myself?
You may be able to replace manually operated, simple dampers without help from an HVAC technician, but complex systems require professionals.
What's the difference between a fire damper and a backdraft damper?
Fire dampers and backdraft dampers serve different functions in HVAC systems. Fire dampers work to prevent the spread of fire through the ductwork and are activated by high temperatures. Backdraft dampers prevent reverse airflow in ventilation systems. They open when air flows in the intended direction and close automatically when airflow stops or reverses.
