HVAC Damper Types - Most of us, when we think of an air damper, think of rushing to a freshly lit fireplace to flip the soot-covered handle that opens the chimney as the room fills with smoke. The HVAC damper is a simple enough concept, directs or redirects airflow in your air conditioning or exhaust system according to your specific requirements. So why are there so many different styles? They range from $5 to $500, so what’s the difference, and which one do you need?
HVAC Damper Types
Damper, I barely know her?
Basic Manual Volume Damper
These are the most typical of the HVAC ductwork dampers. The purpose of these duct fittings is to adjust the air velocity for specific branches of the duct. For example, if you have way too much air coming out of your master bedroom, you can close the damper to that room, either partially or all the way, and the air will be redirected to other parts of the system. Many novices buy these thinking that they can use them to completely shut off a branch of duct, this is not the case. Finally, make sure to read the supply vent myth about this.
These volume dampers, even when all the way closed, still allow some air through. You will notice that even when closed there is a small gap all the way around the blade. These are not for closing off a duct completely, they are simply for “balancing” the airflow in a system to the desired levels. Always make sure you tighten the wingnuts and hardware as tightly as possible so that the blade is locked in place, and so you don’t get an annoying rattling or buzzing sound. Lower-quality fittings will often buzz and rattle, so make sure you’re not cutting corners on quality!
Manual Volume Damper W/Standoff Handle | HVAC Damper Types
The manual volume damper with a standoff handle is required when the sheet metal duct has external insulation. The standoff handle allows the damper blade to be adjusted without being hindered by the insulation. But, these are also a great option for dust collection systems, paint spray booths, smokers, or any application that requires frequent airflow adjustments. At The Sheet Metal Kid, we make them with a slightly thicker gauge of metal, and the handle allows for convenient access and maximum adjust-ability.
Backdraft Dampers (aka Butterfly Damper) | HVAC Damper Types
The purpose of the backdraft damper is exactly what the name suggests, it blocks air from reversing and blowing back into the vent in the wrong direction. For example, you may put these on a fresh air vent that goes out an exterior wall so that the indoor air can go out, but the outdoor air cannot get back into the conditioned space. There are different designs, but most commonly the backdraft damper has a hinge in the center of the balancing blade that only collapses in one direction.
Barometric “Bypass” Damper | HVAC Damper Types
These are rather elegantly designed little fittings with no electricity required, and minimal moving parts. They have a handle similar to the “standoff” style, but there is also a weight that can be slid up or down. These dampers open and allow air to escape when a certain barometric pressure is reached, thus equalizing the air pressure on either side of the metal fitting according to how you have adjusted the weight.
Control Dampers (aka Zone Damper) | HVAC Damper Types
The control damper has an electric motor that can open or close the damper when the temperature control system commands. These are often used for optimizing the air conditioning system by adding zones. Zones are designated in a building according to many criteria; occupancy, solar heat gain, fresh air requirements, etc. You may use a zone damper along with an occupancy sensor so that when a room is occupied the zone damper opens, and when it is not occupied, the zone damper is closed so that air is directed to other zones in the building that are in use.
Fire Damper or Fire/Smoke Damper | HVAC Damper Types
Fire dampers and Fire/Smoke dampers part of the building’s life safety system. They usually require an auxiliary power source that will not be interrupted if the building catches fire. Building codes differ on exactly when these are required, but it’s usually when a duct is penetrating a partition of a certain fire rating. The fire damper automatically closes ventilation when it gets the signal that there is a fire. This closes the air duct so that the fire isn’t fed by the ac system, and slows the fire from spreading to other areas. Fire/smoke dampers are essentially the same thing, except that they also have a smoke sensor, in addition to the fire sensor.
Technical Resource: Refrigeration and Air Conditioning Technology
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