14
08/23
7038-227L
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
appliances 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
I. Negative Pressure
H. Clear Space
Figure 14.1
Maintain 4 ft (1.22m) clearance to
combustibles in front of appliance
NOTE:
Do NOT place combustible objects within
4 ft (1.2m) of the front of appliance
(Figure 14.1)
.
• Mantel:
Avoid placing candles and other heat-sensitive
objects on mantel or hearth. Heat may damage these
objects.
Do NOT place combustible objects in front of the
appliance. High temperatures may ignite clothing,
furniture or draperies.
WARNING
Asphyxiation Risk.
• Negative pressure can cause spillage
of combustion fumes, soot and
carbon monoxide.
• Appliance needs to draft properly for safety.
WARNING
