Dampers control the direction and volume of air flow within a duct to maintain a balanced HVAC system. Most HVAC systems will use dampers in one form or another to control air flow. They are typically located within duct systems and operate as a door that allows, redirects, diffuses, or stops airflow either manually or automatically.
Homeowners should be aware of the various types of dampers to provide energy efficiency for your home. Understanding your dampers can also help with the fire protection of your home. Keep reading to learn more about the common damper types used for HVAC applications, and how they help your system operate.
Common Types of HVAC Dampers
Most residential and light commercial HVAC systems will incorporate some combination of different types of dampers to achieve a balanced system. These include radial, rectangular, round-tube, collar tube, shutter, or blade-style dampers. Industrial applications may require custom-designed dampers, but they generally perform the same function.
While all dampers stop, limit, or redirect airflow, each design offers specific benefits, like better sealing, one-way operation, and precise airflow control. Most dampers are made from galvanized steel, but other materials, like aluminum and stainless steel, are also used depending on the application.
Blade-style dampers, also known as collar-type, 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 the system requires the best seal. They usually have a gasket that glides against the blades as it closes (like a guillotine) 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 reverse flow to move back through the unit. Backdraft dampers are a shutter-style damper commonly found on fans to prevent back pressure.
Radial style dampers use more than one rotating blade to provide very precise air flow control. Radial-style 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, much like balancing dampers. 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 a self-contained unit. Round tube-style dampers will generally replace a short section of flexible ductwork with a short rigid section (less than 24”) 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 either manually or automatically, depending on the application and use of the system. For example, most residential systems will use manually operated blade-style dampers. Usually, contractors adjust and set the blades during initial installation, although it can be changed in the future.
Other HVAC systems require greater control and may include plenum spaces that require airflow restrictions. Often, these dampers are automatically adjusted based on temperature and volume presets and are controlled by the system and a thermostat. Radial-style dampers are common in this configuration due to their greater control capabilities.
Most HVAC dampers will be 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, but not constantly. Often, these dampers are manually controlled via a cable system. Mechanical actuators that open and close the damper are controlled with these cable systems, which are very 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 the time and effort required to simply access a switch. These mechanical actuators are very reliable and rarely need maintenance.
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 that are difficult to manually access, like in a very low attic space.
As an answer 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 by adjusting the rotating blades within the damper. These 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 for each other because both look similar and perform a similar function. Knowing the difference is important, because they are 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. These 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 Opposed Blades
Control dampers are opposed 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 a residential home, even beyond your HVAC system. These dampers allow air travel in one direction only, so they are used in bathroom vent fans, range hoods, and dryer vents as well. Backdraft dampers allow exhaust air to exit the home while outside air pressure prevents reverse air flow.
Butterfly Damper
Industrial HVAC systems sometimes require elaborate airflow control because the structures are so large. For example, 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 in a particular state, or they can be adjusted as needed by the system. Many HVAC systems are divided into control zones, which usually means the rooms that have dedicated ductwork. Each room will have its own ductwork, which means it can be considered a zone.
Similar to a security system, each HVAC zone will be controllable and programmable, providing more consistent air flow and pressure. Multi-zone HVAC dampers can be used in conjunction with other dampers, like backdraft and control dampers to establish the most efficient airflow path. Multi-zone dampers are often controlled continuously by the system and the thermostat.
