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RATE OF EXHAUST FLOW CALCULATIONS
Based on the 1996 International Mechanical Code.
The Rate of air flow required for a vent hood is
calculated using the following definitions (Fig. 6):
Q = Rate of Air Flow in Cubic Feet Per Minute
or [ CFM ] Required for the Hood.
A = Area of Hood Opening in Feet
2
= (L x W)
D = Clearance Height = Distance in Feet from
lower lip of hood to top of dishwasher
chamber.
P = Perimeter of Hood that is Open. This
depends on the hood design, as follows:
If there are four open sides (Island Design), the calculation of the Rate is as follows:
Q = 75 x A
If there are three or fewer open sides, the calculation of the Rate is as follows:
Q = 50 x A
As an alternate method, the Rate can be calculated as follows:
Q = 50 x P x D
Example:
L = 3 W = 3 D = 2
Perimeter Calculation Formula
Hood Design Corner Wall Island
Number of Open Sides 2 Sides Open 3 Sides Open 4 Sides Open
P = L + W L + W + W L + L + W + W
Dimensions Feet Feet Feet
Rate Calculations
Hood Design Corner Wall Island
Number of Open Sides 2 Sides Open 3 Sides Open 4 Sides Open
Q = 75 x A
675 CFM
Q = 50 x A 450 CFM 450 CFM
Q = 50 x P x D 600 CFM 900 CFM 1200 CFM
NOTE: Any listed and labeled factory-built
commercial exhaust hood tested in accordance
with UL Standard 710 by a nationally recognized
testing laboratory, should be installed according
to the terms of its listing and the manufacturer's
installation instructions.
➤
➤
LENGTH
➤
➤
CLEARANCE
HEIGHT
➤
➤
WIDTH
Fig. 6