Fume Hood Fan Sizing
Fume Hood Fan Sizing
(OP)
I was called by a customer. They had someone hook up their conventional fume hood and it isn't passing certification. The certifier said he needs to get 500 cfm when the sash is open 18" and 350 cfm when the sash is at 12". Exhaust duct is 10" round. Trying to find out how to size a new fan to get these sash values. The existing fan is rated at 500 cfm @ .5 wc. At 18" sash opening they are getting around 240 cfm now.





RE: Fume Hood Fan Sizing
One of the more experienced MEs may tell me I'm wrong, so wait around.
1) Measure the differential pressure across the fan with your sash open 18". Then verify that you're still getting 240 CFM thru the hood. You'll need a fan that can deliver 500 CFM at 4X the differential pressure you measured.
OR,
2) Do what I'd do. This is a tiny fan. Buy a big honker (in comparison) and a variable speed control. Set the speed that'll give you what the customer needs.
Best to you,
Goober Dave
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RE: Fume Hood Fan Sizing
RE: Fume Hood Fan Sizing