The Product of a Fan

Fans produce air movement measured in cubic feet per minute (CFM). The best fans have the best value. To calculate the value of a fan, you need to follow this simple formula.

The value of a fan =  Fan Price / CFM of the Fan,  which really boils down to  = Price / CFM

When someone purchases a fan, they’re really purchasing CFM. When deciding which fan to go with, one must first know how much CFM is required. In a tunnel ventilated dairy barn you can calculate this using the formula:

Barn width x average height x desired velocity in MPH x 88 feet per minute = Total CFM Needed


Barn width: 120’
Average barn height: 15’
Desired Velocity: 7 MPH

120’ x 15’ x 7 MPH x 88 fpm = 1,108,800 cfm needed

When you know the total CFM you need, you start fan shopping to know exactly how many fans you’ll need. Remember, each fan produces different amounts of CFM even if the fans you are considering are the same size! At J&D Manufacturing, we have 11 different 72” exhaust fans. Our best producing fan, the Mega Direct Drive, moves 55,505 CFM at 0.10” static pressure (SP). In the case of our example barn, we would need 20 Mega Direct Drive fans to produce the needed 1,108,800 CFM. Our 72” Mega Storm, single phase, no cone moves 38,960 CFM at 0.10” SP. We would need 29 of these fans to produce the required 1,108,800 CFM in the example barn. Even though they are both 72” fiberglass exhaust fans, they produce very different CFM. Some questions to ask are:

  • Do I have enough space in my wall to accommodate 9 additional fans?
  • The Mega Storm is a belt driven fan. Am I willing to do extra maintenance and change out the belts when these fans require it, or do I want maintenance free?
  • What is the cost/CFM?
  • What is the total cost of ownership difference between the fans you’re considering (purchase, labor, install, freight, energy consumption electricity, potential energy rebates, maintenance, parts, warranty, expected life of the fan, disposal, etc.)?

Fans are not created equal. Just because the fans being considered are the same size, does not mean they move the same amount of air. Always #RequestTheTest to verify fan performance and to get a clear picture what your out-of-pocket costs will be when purchasing a new ventilation system. Performance data should be from an AMCA certified chamber or BESS Lab. If it isn’t, the numbers could be estimates and can be drastically inaccurate. If not tested in a chamber, you won’t have Airflow ratio data which is the performance CFM of the fan in the static pressure environment it will be operating in. Many fans look okay under no pressure differential but sputter out under pressure and winds.

Reach out to the #VentilationExperts at J&D Manufacturing. We will provide you with certified performance data on any of our fans you’re considering and help you compare J&D fans to any other competitor fan. We’re happy to help.