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Airflow Testing Procedure
Short Ridge Meter Components
For measuring exhaust airflow rates (cubic feet per
minute = CFM), use a short ridge meter to measure
velocities along the inlet slot of the hood. To ensure
accurate data, all appliances should be on. Multiple
locations need to be tested as outlined below to
ensure an accurate reading.
48 to 72
Hood Length
inches
Minimum Number
of Test Locations
To take velocity readings along the length of the hood,
the edge of the short ridge meter must start/stop six
(6) inches from the end of the hood. Vertical placement
of the short ridge meter along the inlet is shown.
®
72 to 120
120 to 192
inches
inches
3
5
7
After the appropriate number of readings have been
taken from the inlet slot of the hood, an average
reading can be calculated by summing the velocity
readings and dividing the total value by the number of
readings taken.
Average Velocity
=
Next calculate the total hood airflow volume (CFM) by
using the following equation:
Hood CFM = [(Length of Hood in inches x 4.846) x
(Average inlet slot velocity x 2.47)] 144
The constants 4.846 and 2.47 are factory derived for
use with the Grease Grabber™ H
Calculation Example:
Five (5) inlet slot velocity readings (minimum)
Hood Length
Test Location
(off left; in inches)
Velocity Reading (fpm) 175
Average Velocity (FPM) =
(175 + 210 + 250 + 190 + 160) 5 = 197 FPM
Hood Exhaust Rate (CFM) =
[(96 x 4.846) x (197 x 2.47)] 144 = 1572 CFM
Sum of Velocity Readings
Number of Readings
NOTE
O.
2
96 inches
6
27
48
69
210
250
190
Model GGH2O
90
160
21
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