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Negative pressure results from the imbalance of air avail-
able for the fi replace to operate properly. It can be stron-
gest in lower levels of the house.
Causes include:
• Exhaust fans (kitchen, bath, etc.)
• Range hoods
• Combustion air requirements for furnaces, water heaters
and other combustion appliances
• Clothes dryers
• Location of return-air vents to furnace or air
conditioning
• Imbalances of the HVAC air handling system
• Upper level air leaks such as:
- Recessed lighting
- Attic hatch
- Duct leaks
To minimize the effects of negative air pressure:
• Install the outside air kit with the intake facing prevailing
winds during the heating season
• Ensure adequate outdoor air for all combustion
appliances and exhaust equipment
• Ensure furnace and air conditioning return vents are not
located in the immediate vicinity of the fi replace
• Avoid installing the fi replace near doors, walkways or
small isolated spaces
• Recessed lighting should be a “sealed can” design
• Attic hatches weather stripped or sealed
• Attic mounted duct work and air handler joints and seams
taped or sealed
• Basement installations should be avoided
WARNING! Risk of Asphyxiation! Negative pressure
can cause spillage of combustion fumes and soot. Fire
must draft properly for safe operation.
NOTICE: Hearth & Home Technologies Inc. recommends
the use of direct vent fi replaces in basements.
D. Negative PressureB. Design and Installation Considerations
Draft is the pressure difference needed to vent fi replaces
successfully. When a fi replace is drafting successfully, all
combustion byproducts are exiting the home through the
chimney.
Considerations for successful draft include:
• Preventing negative pressure
• Location of fi replace and chimney
Before installing, determine the following:
• Where the fi replace is to be installed.
• The vent system confi guration to be used.
• Gas supply piping.
• Electrical wiring.
• Framing and fi nishing details.
• Whether optional accessories—devices such as a fan,
wall switch or remote control —are desired.
NOTICE: Check building codes prior to installation.
• Installation MUST comply with local, regional, state and
national codes and regulations.
• Consult insurance carrier, local building inspector, fi re
offi cials or authorities having jurisdiction over restrictions,
installation inspection and permits.
NOTICE: Hearth & Home Technologies assumes no
responsibility for the improper performance of the fi replace
system caused by:
• Inadequate draft due to environmental conditions
• Downdrafts
• Tight sealing construction of the structure
• Mechanical exhausting devices
• Improper location of the chimney
C. Draft
Heatilator • A36C & A42C • 28396 • Rev AG • 11/08