Installation manual

Balancing the Air Flows with a Pitot Tube (applicable to All Models)
STEP 1. D
rill a 3/16” hole in the duct (ideally 3 feet downstream of
a
ny elbows or bends and 1 foot upstream of any elbows
o
r bends) in the Fresh Air and Stale air streams.
Note:
T
he duct configuration in these illustrations may
v
ary from the duct configuration on your model.
CORE
Stale Air From Building Fresh Air to Building
Balancing
Damper
Balancing
D
amper
Drill 3/16” holes in
Stale & Fresh Air
ducts
CORE
Stale Air From Building Fresh Air to Building
STEP 2. I
nsert the Pitot tube with the tip facing towards the air
stream in the Stale Air From Building air stream. Move
the Pitot tube around in the duct (facing towards the
airflow) and take an average reading. Record the reading.
Pitot tube tip facing
towards the air stream
M
A
G
NE
H
E
L
I
C
Magnehelic Gauge must be level
CORE
Stale Air From Building
Fresh Air to Building
Pitot tube tip facing
towards the air stream
M
AG
N
E
H
E
L
I
C
Magnehelic
Gauge must
be level
STEP 3. Repeat Step 2 to measure the Fresh Air to Building duct.
STEP 4.
A) Review the readings and damper down the duct with the
highest duct velocity pressure. Repeat Step 2 and Step 3
until both ducts show identical readings. For this example,
the Fresh Air to Building air stream has the highest duct
velocity pressure.
Damper down the duct with the
hightest duct velocity pressure
B) Seal the holes upon
completion of the balancing
Determining the cfm
After balancing the air flows, calculate the cfm flow rate.
Example
This example shows how to determine the air flow for a 6” diameter
duct. As shown in the illustration, the duct velocity pressure reads
0.025” w.c. on the magnehelic gauge. Use the chart that came with
the magnehelic gauge to determine a duct velocity of 640 feet per
minute for a duct velocity pressure of 0.025” w.c.
Cfm Calculation
cfm = feet per minute x cross section area of duct
= 640 x 0.196
= 125
Cross Section Area of some common round duct sizes:
0.087 for 4” diameter duct
0.136 for 5” diameter duct
0.196 for 6” diameter duct
0.267 for 7” diameter duct
Magnehelic Gauge reading .025” w.c.
27