DIYbanter - View Single Post - Calculating Ventilation fan / vent "free area"

DT

In article .com,
says...

Consider a room that measures 8' x 10' x 8', or 640 cubic feet.
I want to install a fan and vents that will exchange the air in this
room about once every 2-3 minutes, so a fan should be rated in the
range of 210 - 320 cfm.

I need some guidance in how to calculate the appropriate free area of
the vent(s) that will allow the fan to pull air from adjoining rooms
through this room.'

That's a heck on an exchange rate, higher than a clean room! Anyway, for a
quickie estimate, select your fan first and see what size duct it uses. I'm
guessing an 8" round duct. Of course, you don't need your intake air velocity
to be anywhere near as fast as the exhaust, so start with maybe double the fan
exhaust area. For an 8" fan, of 50 square inches, 100 square inches would
give you half the exhaust velocty, 150 would give you 1/3, etc. And if you want
efficient 'washing', the intakes need to be distributed in the correct areas.

--
Dennis