Determining The Cfm - Airia LIFEBREATH ERV Serie Guide D'installation

Determining the CFM

After balancing the airflows, calculate the CFM flow rate.
Example
This example shows how to determine the airflow for a 6 in
diameter duct. As shown in the illustration, the duct velocity
pressure reads 0.025 in w.g. on the magnehelic gauge. Use
the chart that came with the pitot tube to determine a duct
velocity of 640 ft/min. for a duct velocity pressure of 0.025 in
w.g.
CFM Calculation
CFM = feet per minute x cross section area of duct
= 640 x 0.196
= 125
Units with Balancing Collars
Install these units with the dampers fully open and damper down the duct with the higher airflow
to equal the lower airflow. Refer to the "Balancing the Airflows" page found in this manual.
All other units require dampers for balancing airflows installed into the "Fresh Air to Building" and
"Stale Air from Building" ductwork.
Attention
 Installations where the ERV is ducted directly to the return of a furnace may require additional dampening on the
fresh air to building duct. This is due to the high return static pressures found in some furnace installations.
Push and turn with slotted
screwdriver. Damper automatically
locks when pressure is released.
Hard/Rigid ducting
Cross section area of some common
duct sizes:
0.087 for 4 in duct
0.139 for 5 in duct
0.196 for 6 in duct
0.267 for 7 in duct
When connecting ductwork to the
collar, take note where screws are
located. Screws should be located
no further than 1/2 in from
outside edge of collar, so as not
to impede operation of the
damper.
1/2 in
Insulated flexible ducting
Magnehelic
Gauge reading
0.025 in w.g.
18