8
This is an example for determining the airflow in a 6-in.
duct. The pitot tube reading was 0.025 inches of water. From
the chart, this is 640 feet per minute.
The 6-in. diameter duct has cross-sectional area of:
Area = Pi x Radius
2
6-in / 2 = 3-in. radius
3-in. /12 = 0.25 ft radius
A = 3.14 x (0.25)
2
A = 0.2 sq ft
The airflow is then:
640 ft/min x 0.2 sq ft = 128 cfm
For convenience, the cross sectional area of some common
round ducts are listed below:
The accuracy of the airflow 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.
BALANCING DAMPER ADJUSTMENT — Installation
where the HRV 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 fur-
nace installations.
A butterfly damper is provided for field-installation in the
fresh air to building duct. Install the damper and adjust as
necessary.
DUCT DIAMETER (in.)
AREA (sq ft)
5
0.14
6
0.20
7
0.27
8
0.35
FORCED AIR
FURNACE
COOL AIR
RETURN
RETURN AIR
1 M
(3’-3") MIN
RECOMMENDED
* UNIT IS NORMALLY BALANCED ON HIGH SPEED
WITH FURNACE BLOWER ON.
OUTDOORS
* DUCTS CONNECTION MAY VARY
DEPENDING ON MODEL
1 M
(3’-3") MIN
RECOMMENDED
NOTES:
1. Furnace blower may be required to operate when ventilation from HRV is required. The furnace should be set to run continuously or inter-
locked with HRV.
2. The exhaust air connection should be upstream of the supply air connection to prevent exhausting any fresh air.
3. Weather hood arrangement is for drawing purposes only. 6
′
(2 m) minimum separation recommended. 18
″
(460 mm) above grade minimum.
4. Due to the differences in pressure between the HRV and the equipment it is being connected to, the HRV’s airflow must be confirmed on site,
using the balancing procedure found in the installation manual.
Fig. 20 — Direct Connection to Furnace (Supply/Return) Airflow Diagram
.
.
.
.
.
Fig. 21 — Secure Airflow Station
Fig. 22 — Magnehelic Gage
Fig. 23 — Adjust Damper Position
