Make-Up Air Application Guide

Broan Automatic Make-Up Air Damper Product Guide – 04-17-13 13
7.1.1 Using the On-line Range Hood Make-Up Air Specifier
The Range Hood Make-Up Air Specifier (the “Tool”) takes the guess work out of specifying
code-compliant make-up air systems by customizing an engineered design based on user-
entered building and system characteristics. All Tool inputs are selected using dropdown lists.
Most of the inputs in the Tool are straightforward, including duct characteristics like length,
dimension, roughness, and configuration (for example, does the outdoor air duct feed into the
return trunk of the central air handler, and does the central air handler operate automatically
when the Damper opens?); range hood model and rated flow; and home characteristics like
leakage rate to outside, ceiling height, and floor area. See the following schematic for an
illustration of Tool inputs and outputs.
Of the Tool inputs, the least familiar is probably the home’s
“design depressurization limit”. Depressurization can occur when
the exhaust appliances in a home cause it to operate at a lower
pressure than outdoors. The greater the depressurization, the
more make-up air will be introduced across cracks and gaps in
the building envelope and across the Broan Automatic Make-Up
Air Damper. However, the greater the depressurization, the
more difficult it is for exhaust appliances and some combustion
appliances to work as designed. The design depressurization
limit is the user-targeted value that sizes the make-up air
Damper(s) to avoid compromising the performance of exhaust
and combustion appliances. See the Definitions section of this
Guide or the Tool itself for information on industry guidance in
selecting a design depressurization limit.
Design Exhaust Rate
 Range Hood Flow
 Range Hood Selection
 Exhaust Duct Dimension
 Exhaust Duct Length and Elbows
 Additional Exhaust Rate, if Any
 Design Depressurization Limit
 Floor Area in Pressure Boundary
 Average Ceiling Height
 Home Leakage Rate to Outside
 Combustion Air Openings
Building Leakage at Design Depressurization
 Design Depressurization Limit
 Outdoor Air Duct Surface Roughness
 Outdoor Air Duct Length and Elbows
Flow through Automatic Make-Up Air
Damper(s)
 State
State-level Code Make-Up Air Requirements
 County
Climate-Specific Installation Considerations
 Tool In
p
uts
Tool Outputs
Frequent users of the Tool will
discover that very tight dwellings with
natural vented combustion appliances
may require multiple Dampers to
satisfy code requirements. In this
case, consider specifying
mechanically vented combustion
appliances or direct vent appliances,
which can typically withstand higher
design depressurization limits, leading
to more make-up air introduced
through the Dampers and across
cracks and gaps in the building
envelope. Another option for
increasing the make-up air flow rate is
connecting the Damper to the return
side of the central duct system.