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Broan Automatic Make-Up Air Damper Product Guide – 04-17-13 14
One of the key functions of the Tool is its ability to allow users to take credit for make-up air that
is supplied through cracks and gaps within the building envelope. While the building code
requires that some of the make-up air for range hoods over 400 cfm be provided through a
system that can be “automatically controlled to start and operate simultaneously with the
exhaust system” (e.g., the Broan Automatic Make-Up Air Damper), it also recognizes that some
make-up air can be provided through air leakage across the building envelope. Using
engineering equations
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, the Tool makes it easy to estimate the expected amount of make-up air
that can be provided at the user-selected design depressurization limit, both naturally through
leakage across the building envelope and intentionally through automatically opening the
Damper(s). To avoid double-counting building openings used for combustion air, the Tool has
the user input the cross sectional area of any combustion air openings for combustion
appliances that are not direct-vent appliances.
Finally, the Tool outputs a cut-sheet of the recommended make-up air solution, including a list of
user-selected range hood, Damper(s), design performance characteristics, and information that
can be submitted to the code official to demonstrate code compliance.
7.1.2 Simplified Sizing in the Absence of Building Codes
The Tool is configured to provide code-compliant make-up air system specifications for kitchen
exhaust systems exceeding 400 cfm. In the case where make-up air is not required by code, but
the designer believes that the building’s performance would benefit from installing the Broan
Automatic Make-Up Air Damper, the following rule of thumb is offered: Select a Broan
Automatic Make-Up Air Damper such that the Damper diameter is greater than or equal to the
exhaust duct diameter.
7.1.3 Testing
Regardless of the make-up air sizing method selected, Broan highly recommends that a
qualified HVAC professional be consulted after installation to ensure that the
Damper opens and closes as designed,
Depressurization is not excessive during operation of exhaust appliances, and
Exhaust and combustion appliances operate as designed.
Where combustion appliances are located within a home’s pressure boundary, a combustion
appliance zone test performed by a qualified HVAC professional is recommended. Note that
other systems and features of the home can also create negative pressures in the home relative
to outdoors, and that the Damper is not intended to address these.
7.2 Outdoor Air Intake Location
Proper design and location of the outdoor air intake location is critical in ensuring that the
Damper can safely and reliably provide an opening for fresh outdoor air to enter the home. The
following requirements for the location of the outdoor air intake should be met:
- Outdoor air intake is located a minimum of 10’ from combustion appliance vents,
chimneys, plumbing stacks, and bathroom or kitchen exhaust vents. If local codes have
more stringent separation requirements, they shall apply.
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The Tool uses the Darcy-Weisbach equation and others sourced from ASHRAE Fundamentals 2009,
Chapters 16 and 21.
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