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Broan Automatic Make-Up Air Damper Product Guide – 04-17-13 15
- If integrated with the return trunk of the central duct system, the outdoor air intake is
located at least 10’ from the HVAC appliance.
- Outdoor air intake is placed high enough above grade to prevent blockage from snow or
other debris such as leaves, and at a minimum of 1’ above grade.
- Make-up air damper should not
draw air from crawlspaces, garages, attics, adjacent
dwelling units, or any enclosed part of the building. The Damper should be installed to
draw air directly from outdoors.
7.3 Outdoor Air Intake Opening Protection
Because the Damper, together with the end cap and outdoor air duct which are installed with it,
will allow outdoor air into the indoor environment, it is important to meet the following
requirements:
- Install the protective screen provided with your Damper to protect the opening to the
outdoor air duct
- If a protective screen other than the screen provided with your Damper is used, it must
cover the entire opening of the outdoor air duct. This screen must also have openings of
at least ¼” but no larger than ½”
- The outdoor air intake opening should meet local code provisions for the protection of
openings in exterior walls, including steps to prevent moisture intrusion around the
opening.
Note that the screen over the outdoor air opening is not a filter. It is intended to prevent the
intake of leaves, animals, or debris into the outdoor air duct. A downstream filter is necessary to
remove pollen, dust, and other airborne particles. Potential filter locations are shown below in
the Typical Installations section (section 8).
7.4 Climatic Considerations for Outdoor Air (OA) Ducts Connected to Central Duct Systems
If connecting the OA duct to the return side of a central duct system, check to see if the HVAC
equipment manufacturer has any minimum requirements for the air temperature in the return air
plenum (a minimum of 60°F return temperature for gas-fired forced air furnaces is
recommended by some manufacturers). The installer should adjust both the size of the OA duct
and the location of its connection to the return side of the central duct system so that minimum
air temperature requirements are satisfied under design conditions. While the volume of OA
that can be provided will vary between locations, the following guidance is offered as a rule of
thumb:
International Energy
Conservation Code
Climate Zone
Maximum Recommended
Outdoor Make-Up Air Flow as %
of Total Furnace Air Handler Flow
1 No limit
2 40%
3 30%
4 25%
5 20%
6 15%
If necessary, homes with more than one central HVAC system may increase the OA volume by
installing OA ducts with Dampers on each system.
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