16
7038-227C
August
13,
2018
57ST-ACC-C
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
K. Clear Space
• Do NOT place combustible objects within 4 ft (1.2 m) of
the front of appliance
(Figure 16.1)
.
• Mantel - avoid placing candles and other heat-sensitive
objects on mantel or hearth. Heat may damage these
objects.
Figure 16.1
Maintain 4 ft (1.22m) clearance to
combustible in front of appliance
WARNING
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.
