Harman® • P35i-C Installation Manual_R2 • 2019 -___ • 02/20
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8390-784i
F. Negative Pressure
WARNING! Risk of Asphyxiation!
Negative pressure can
cause spillage of combustion fumes and soot.
Negative pressure results from the imbalance of air available
for the appliance to operate properly. It can be strongest 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 appliance
• Avoid installing the appliance 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
NOTICE:
Hearth & Home Technologies assumes no
responsibility for the improper performance of the chimney
system caused by:
• Inadequate draft due to environmental conditions
• Down drafts
• Tight sealing construction of the structure
• Mechanical exhausting devices
G. Avoiding Smoke and Odors
Avoiding Smoke and Odors
Negative Pressure, Shut-down, and Power Failure:
T
o reduce the probability of back-drafting or burn-back in
the pellet burning appliance during power failure or shut-
down conditions, the stove must be able to draft naturally
without exhaust blower operation. Negative pressure in the
house will resist this natural draft if not accounted for in the
pellet appliance installation.
Heat rises in the house and leaks out at upper levels. This
air must be replaced with cold air from outdoors, which flows
into lower levels of the house. Vents and chimneys into
basements and lower levels of the house can become the
conduit for air supply, and reverse under these conditions.
Outside Air:
Hearth & Home Technologies recommend attaching
outside air in all installations, especially lower level and
main floor locations.
Per national building codes, consideration must be given to
combustion air supply to all combustion appliances. Failure
to supply adequate combustion air for all appliance demands,
may lead to back-drafting of those and other appliances.
When the appliance is side-wall vented: The air intake is best
located on the same exterior wall as the exhaust vent outlet
and located lower on the wall than the exhaust vent outlet.
When the appliance is roof vented: The air intake is best
located on the exterior wall oriented towards the prevailing
wind direction during the heating season.
The outside air connection will supply the demands of the
pellet appliance, but consideration must be given to the
total house demand. House demand may consume some
air needed for the stove, especially during a power failure. It
may be necessary to add additional ventilation to the space in
which the pellet appliance is located. Consult with your local
HVAC professional to determine the ventilation demands for
your house.
