Exhaust fan calculations

  • Thread starter JoshDeM
  • Start date
I've been given some specifications by a company for an exhaust fan that I am looking at purchasing for my company. They tell me it is 10,900 cfm. Then given some specs on the electrical requirements. I am wondering with the information given could I check their given flow rate?

I imagine that I will need to make a few assumptions along the way. I want to make sure they aren't out to lunch.
Below are the specs

The actual volume for the fan will depend on inlet and outlet conditions. The manufacturer will have (or you may not want to do business with them) a fan curve showing the relationship between pressure and flow. unless you're using it with no ducts and no restrictions, you'll need to figure out where your system curve intersects their fan curve. Figuring out your system curve can be a real PITA.
you'll need to figure out where your system curve intersects their fan curve.
Yes! The single published CFM number isn't very useful in design, it's really for sorting fans to consider more carefully. Start by finding the "fan curve" (CFM vs. pressure) in the data sheet. Notice that for almost every fan you will actually get much lower CFM than that single number at most pressures. Systems are usually designed to operate in the middle, flatter part of the fan curve, where the flow is less sensitive to back pressure. It is your system (enclosure, ducting, etc.) that will determine the pressure that the fan will experience. As Dullard said, your system has its own flow vs. pressure curve.

Want to reply to this thread?

"Exhaust fan calculations" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads