With so many dampers being used in the HVAC industry the sizing of an electronic actuator like Belimo, Johnson Controls, and Honeywell is critical.

No matter if the electronic actuator is spring return or non-spring return the proper torque rating (in-lb += inch pounds) of the actuator is necessary to drive the blades of the damper in a open or a closed position. So the first step in selection of the proper damper actuator is to find the damper’s square footage AREA. A simple formula of Width X Height divided by 144 will give you the square footage of a damper.

Example: The damper in question is 45 inches X 23 inches using the formula. 45 X 23 = 1035 divided by 144 = 7.1875 square feet of damper area.

The next important piece of information is the type of damper you need the actuator for.

1. NO SEALS….. Usually an outside air damper

2. WITH SEALS….. Usually interior dampers like zone control dampers

3. Fire/Smoke dampers

NO SEALS dampers require 7 in-lb of torque per square foot of damper area to open/close the damper blades *

WITH SEALS dampers require 8 in-lb of torque per square foot of damper area to open/close the damper blades *

FIRE/SMOKE dampers require 9 in-lb of torque per square foot of damper area to open/close the damper blades *

* ( Less than 1000 feet per minute air flow)

Multiply 7, 8, or 9 by the damper’s square footage to arrive at the minimum torque value needed by the actuator motor to open and to close the damper. Note: If the torque necessary is too close to the actuators maximum torque valve go to the next highest torque value actuator.

With this in mind let’s look at the different torque requirements for the example above.

The square footage of our damper is 7.1875 square feet

NO SEALS damper = 7.1875 X 7 = 50.3125 in-lbs of minimum torque necessary

WITH SEALS damper = 7.1875 X 8 = 57.50 in-lbs of minimum torque necessary

FIRE/SMOKE damper = 7.1875 X 9 = 67.3875 in-lbs of minimum torque necessary

Industrial dampers will usually have different requirements for the sizing of electronic damper actuators but this simple formulas can be used on domestic and commercial sizing of actuatrors. If you need help sizing your damper actuators pleases give Stromquist and Company a call at 1-800-241-9471 and we can help you in the selection process.

Bob Jordan says

Great post Mr. Jones, this is very useful information. Thanks.

Bill Jones says

Bob Jordan…. Thank you for the comment. We at Conrol Trends really appreciate comments on the articles.

Taz says

Keep it up! , Useful post

Osaid says

Thanks a lot for this information

I am an engineer working with international company for AC equipment

And I am trying to find a formula to calculate the “minimum torque necessary”

But i need this formula to be related to damper pressure drop

Anybody can help me?