When it comes to building safety, it helps to understand the components that prevent and contain fire. Fire dampers play a pivotal role among them. Designed to stop fire from spreading through ductwork, they are integral to the safety infrastructure of any building. They give occupants time to evacuate safely and give first responders time to do their jobs.
Selecting the right fire damper for the application is key to ensuring a building performs as designed should disaster strike.
Fire dampers are grouped in several ways. By blade design, they are curtain or multi-blade, and by trigger, they are fire, smoke, or combination dampers. They are also classified as static or dynamic based on airflow during a fire. Frame style adds another layer, with Type A, Type B, and Type C/CR models that differ in how much the blade stack blocks the airstream. Ceiling radiation dampers are a separate type used in fire-rated ceilings.
Over the years, building codes have evolved based on lessons learned from past fires and disasters. One of those lessons is that occupants need a fire-reinforced path to evacuate. When designing a building, certain wall and ceiling assemblies may require fire ratings to protect that path. Fire ratings are measured in hours, which represent how long an assembly can resist a fire before failing.
A fire damper is a safety device installed in HVAC ductwork where the duct passes through a fire-rated boundary. Fire dampers are tested and listed to UL 555. Assemblies rated under 3 hours use 1½-hour dampers, while assemblies rated 3 hours or more use 3-hour dampers.
Without a fire damper, these duct openings would create a weak point that could allow fire to spread. During a fire, the damper closes automatically, usually triggered by a thermal element called a fusible link. Standard links release at about 165°F. Higher-temperature links are available for systems that run warm. This mechanism keeps fire contained to one area, a core strategy in fire safety known as compartmentalization.
Not all fire dampers are created equal. Dampers come in many varieties to suit different applications, and they are classified by blade type, trigger, airflow condition, and frame style.
Fire dampers use two major blade designs: curtain blade and multi-blade, available in 3V or airfoil (AF) styles. Curtain blade dampers are often thought of as the standard design, and they are typically cheaper to manufacture. When triggered, the blades fall like a curtain.
Multi-blade dampers sit in the airstream and rotate via a linkage to close off airflow. The blades can even be designed in low-leakage configurations for a very tight seal, even at high static pressure.
Simply put, fire dampers are triggered by fire and smoke dampers are triggered by smoke. Combination dampers respond to either one. All three work in a similar way, releasing a blade stack or rotating blades to stop the flow of air. Code requirements typically dictate which type is needed. For every type, regular inspection of the damper helps ensure it is ready to respond.
Smoke and combination dampers close using life safety actuators. These actuators are often tied to duct smoke detectors or the building's fire alarm system.
Dampers can be either static or dynamic. Static fire dampers are typically gravity-assisted. They are designed for HVAC systems where the fans turn off in the event of fire or smoke.
Some air handling systems are designed to keep running during a fire so they can pressurize certain compartments. These systems need dynamic fire dampers, which use springs or other mechanisms to force the damper closed. Because UL 555 rates them to close against a set airflow and pressure, dynamic dampers cost more than static models.
Beyond static and dynamic, fire dampers also come in Type A, Type B, and Type C varieties.
Type A fire dampers have blades that sit in the airstream. They cause a higher pressure drop, but they are easy to install and less expensive to manufacture. These dampers work best where blade stack intrusion is not a big concern. Pressures should also be fairly low, typically under 3" w.c.
Type B fire dampers lower the pressure drop by moving the blade stack out of the airstream. With nothing in the way, air passes through easily. Short ducts (typically under 12" tall) and high velocity ducts benefit the most. In a short duct, a Type A blade stack blocks a larger share of the free area, and Type B solves that problem.
Type C (square/rectangular) and CR (round) fire dampers are the highest performing type. They typically have a collar for easy duct installation and are designed for medium to high velocity ductwork. Like Type B, they fully remove the blade stack from the duct area to maximize free area. Type C and CR dampers can handle high pressures, often up to 10" w.c. They can also be configured with transition collars to connect to round or oval ductwork.
Ceiling radiation dampers protect openings in fire-rated floor/ceiling and roof/ceiling assemblies, such as where a diffuser or grille sits in a rated ceiling. Rather than stopping flames inside a duct, they limit radiant heat moving into the space above. They are tested to UL 555C and must be installed as part of the specific rated assembly design.
When comparing Types A, B, and C/CR, start with the environment and requirements of the HVAC system. Cost typically goes up as you go down the alphabet, with Type A being the cheapest and Type C the most expensive. Type C dampers can be used in any application. Type B dampers can be used in place of Type A. Type A dampers should only be used when blade stack intrusion into the airstream is not a concern.
For each location, choose the lowest-rated fire damper that meets the application requirements. Over-specifying leads to excess cost and over-engineering. Using only Type C dampers where Type B or Type A would work is a common example. The right choice depends on the specific needs of the building and its HVAC system, so it deserves careful consideration.
Choosing United Enertech for your fire damper needs means opting for quality, compliance, and customization. Our products are known for durable construction and adherence to strict safety standards. Because dampers can be customized to specific requirements, every building gets an effective and efficient fire protection solution. Browse the full line of UL-listed fire and smoke dampers to compare options.
To learn more about fire dampers and the difference between Type A, Type B, and Type C, reach out to the fire damper experts at United Enertech today!
Fire dampers are classified by blade design, trigger, airflow condition, and frame style. That includes curtain and multi-blade dampers, fire, smoke, and combination dampers, static and dynamic dampers, and Type A, B, and C/CR dampers. Ceiling radiation dampers are a separate category for rated ceilings.
The main difference is where the blade stack sits. Type A blades sit in the airstream, which adds pressure drop, while Type B moves the blade stack out of the way. Type C/CR removes it fully from the duct area and adds a collar, making it the best fit for high velocity and high pressure systems.
A static fire damper closes by gravity and is used where fans shut down during a fire. A dynamic fire damper is rated to close against moving air. It is the right choice when fans keep running during a fire.
A fire damper closes in response to heat, usually when a fusible link melts. A smoke damper closes when it receives a signal from a smoke detector or fire alarm. A combination fire/smoke damper does both.
Fire dampers are tested to UL 555, and smoke dampers are tested to UL 555S. Combination dampers meet both standards. Ceiling radiation dampers are tested to UL 555C.
Most fire dampers use a fusible link that releases at 165°F. For systems with higher operating temperatures, higher-temperature links are available.
Fire dampers are generally required where ductwork passes through fire-rated walls, floors, and partitions. These requirements come from the International Building Code, NFPA 90A, and local code. The project engineer and local code official determine the exact locations.
NFPA 80 and NFPA 105 call for testing within one year of installation, then every four years after that. Hospitals follow a six-year cycle instead. See our fire damper inspection guide for details.
