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Fume Hood

“The calculation for the CFM of a fume hood is obtained by multiplying the total opening (comprised of the face opening and the bypass opening) and the face velocity.

The face opening is defined as the width of the sash opening multiplied by the height of the sash opening. The bypass opening is defined as the area of additional opening above and below the sash. The bypass performs an important role by allowing air to enter the hood while the sash is closed and preventing the buildup of chemical fumes.

The face velocity is the speed of the air entering the hood, expressed in units of feet per minute (FPM). The typical range of face velocity falls between 80 FPM to 120 FPM, although new high performance fume hoods like the Kewaunee Venturi fume hood can be operated as low as 50 FPM. “

Kewaunee Fume Hoods

Model Number
Fume Hood Values
Opening Width
(In Inches)
Opening Height
(In Inches)
Face Velocity
(In FPM)
Bypass Area
(In SQ FT)
Number of
Duct Collars
Size of Duct Collar
(In Inches)

CFM diagram

A C D B B - Opening Height C - Bypass Opening D - Duct Connection A - Opening Width 0 0 0 0 - - - - inches inches Sq. Feet inches
Kewaunee Fumehood
Exhaust (CFM))
Duct SP

FACE OPENING Calculation:
22″x 12″= 264 square inches.
Divide this by 144 to get Square Feet. 264 ÷ 144 = 1.83 square foot opening

You would now multiply this area measurement (1.83sq.ft.) by your desired FACE VELOCITY, in this case 100fpm and that will give you the CFM requirements you need.
1.8 square feet x 100 fpm = 180 CFM
So in this case, you would need your exhaust fan to be able to draw 180 CFM. Our catalog listing for 50000-0002 lists that an even 200 CFM needed, rounding up from the 180 CFM calculated here. Getting to here is the easy part. To determine how powerful a fan is needed, you still need to calculate the length of exhaust pipe (including turns) leading from the fume hood to the end exit point. The longer the distance and the more cu

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