Lifebreath 2000EFD - Airflow Balancing Example; Calculating Airflow and Duct Sizing

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Page 16
BALANCING THE AIRFLOWS
Example:
This is an example for determining the airflow in a 6 in. (0.5 ft) duct.
• The Pitot tube reading was 0.025 inches of water. From the chart, this is 640 ft/min.
The 6 in. (0.5 ft) duct has a cross sectional area of:
A = πr
2
= [πd
2
] / 4
A = [3.14 x (0.5 ft)
2
] / 4
A = 0.2 ft
2
The airflow is then: (640 ft./min.) x (0.2 ft
2
) = 128 cfm
For your convenience, the cross sectional areas of some common duct sizes are listed below:
DUCT. DIAM. (inches)
CROSS SECTION AREA (sq. ft.)
5 (127 mm)
0.14
6 (152 mm)
0.20
7 (178 mm)
0.27
The accuracy of the air flow reading will be affected by how close to any elbows or bends the readings are
taken. Accuracy can be increased by taking an average of multiple readings as outlined in the literature
supplied with the Pitot tube.
Note: Place pitot tube a minimum
of 18” from blower or elbows
Note: Duct connections may
vary, depending on model.