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.
Hood Length | 48 to 72 | 72 to 120 | 120 to 192 | |
inches | inches | inches | ||
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Minimum Number | 3 | 5 | 7 | |
of Test Locations | ||||
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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.
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.
Sum of Velocity Readings
Average Velocity =
Number of Readings
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
NOTE
The constants 4.846 and 2.47 are factory derived for use with the Grease Grabber™ H2O.
Calculation Example:
Five (5) inlet slot velocity readings (minimum)
Hood Length | 96 inches |
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Test Location | 6 | 27 | 48 | 69 | 90 | |
(off left; in inches) | ||||||
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Velocity Reading (fpm) | 175 | 210 | 250 | 190 | 160 | |
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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
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Model GGH2O 21
