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• A positive or negative pressure may occur in the house
• HRV/ERV may not operate at its maximum efficiency
• The unit may not defrost properly
Air Flow Measuring Gauges
The magnehelic gauge and the digital manometer are suitable
instruments for the balancing of air flows.
A magnehelic gauge with a scale of 0 to .25" w.c. is suitable
for accurately measuring air duct velocity. The value on the
gauge will be velocity pressure. A digital manometer requires
the ability to display differential pressures at 3 digits of
resolution.
Gauge Attachments
When sampling an air flow, various attachments are available
for use on a magnehelic gauge or digital manometer.
The following illustration shows a magnehelic gauge with
a scale of 0 to .25" w.c. with a pitot tube attachment. This
combination will measure the system air velocity pressure
accurately, regardless of the duct size or shape (either round
or rectangular).
Balancing Preparation
Prior to performing the air balancing procedure, perform the
following steps:
• Seal the ductwork system
• Confirm the installation and proper operation of all the
components of the HRV/ERV
• Fully open the balancing dampers
• Turn off all household exhaust devices (range hood, clothes
dryer, bathroom fans)
• Set the HRV/ERV at high speed
• Prior to balancing the unit, first adjust air flows in branch
lines to specific areas of the house
• If the outdoor temperature is below 0˚C (32˚F), ensure the
unit is not running in defrost
• Place the magnehelic gauge on a level surface and adjust it
to zero
• If the system is a Simplified or Partially Dedicated
installation, operate the furnace/Air Handler at high speed
M
A
G
N
E
H
E
LI
C
DUCT
AIR
FLOW
Pitot tube
High Pressure Side
Low Pressure Side
Magnehelic gauge
Pitot tube and gauge
Balancing the Air Flows
Continuous, excessive, positive pressure may
drive moist indoor air into the external walls of
the building. Once inside the external walls, moist
air may condense (in cold weather) and degrade
structural components or cause locks to freeze.
Continuous, excessive, negative pressure may
have several undesirable effects. In some
geographic locations, soil gases such as methane
and radon gas may be drawn into the home
through basement or ground contact areas, and
may also cause the backdrafting of vented
combustion equipment.
ATTENTION
Magnehelic Gauge with a scale of 0 to .25” w.c.
Magnehelic Gauge (scale of 0 to .25” w.c.)
with a Pitot Tube Attachment
Balancing the air flows is critical to ensuring that the amount of air introduced from the outside of the building equals the
amount of air exhausted to the outside of the building. If these two air flows are not properly balanced, the following issues
may occur: