DUCT DIAM.
5"
6"
CROSS SECTION AREA
0.136 sq. ft.
0.196 sq. ft.
The accuracy of the 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 of the Pitot tube.
MAGNEHELIC
0
.1
.2
.3
.4
.5
MAGNEHELIC
0
.1
.2
.3
.4
.5
Magnehelic
gauge
Pitot
tube
Pitot tube
Min 3 ft straight duct
(option #1)
Min 3 ft straight duct
MAGNEHELIC
0
.
1
.2
.3
.4
.5
(option #2)
Note: To take more accurate readings, use option #1(if possible).
(Option #2)
- Remove plug from #2 and #4 locations as
shown for balancing
- Do not use pitot tube to open holes in the
insulation as it may block/damage the pitot tube.
- Take 3-4 readings on each hole and average
for supply side and same for exhaust.
- After finish balancing, plug both two holes back
to avoid air leakage and whistling noise from
the holes.
CFM = Opening / Cross-sectional Area(sq.ft.) x velocity(FPM)
Ø5
0.010 50
0.012 60
0.016 70
0.022 80
0.027 90
0.034 100
0.041 110
0.048 120
0.057 130
P"
CFM
P" = Velocity Pressure in inch
Air Flow Balancing (cont’d)
#2#2
#3#3
MAGNEHELIC
0
.1
.2
.3
.4
.5
Remove plug
while balancing
Remove plug
while balancing
#1
#4
10
Plugs
Rev(1.0), 07/02/15
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