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6 Heatilator • RBV4236/RBV4842 • 4048-210 Rev K • 02/07
B. Negative Pressure
Asphyxiation Risk
• Negative pressure can cause spillage of
combustion fumes and soot.
• Fire needs to draft properly for safe
operation.
WARNING
To minimize the effects of negative air pressure, the follow-
ing must be considered:
• Install the outside air kit. Install the intake on the side of
the house towards prevailing winds during the heating
season.
• Ensure adequate outdoor air is supplied for 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 due to stack
effect. Stack effect creates negative pressure in lower
levels. Hearth & Home Technologies recommends the
use of direct vent fi replaces in basements.
Location of the fi replace and chimney will affect performance.
As shown in Figure 2.1 the chimney should:
• Be installed through the warm airspace enclosed by the
building envelope. This helps to produce more draft,
especially during lighting and die-down of the fi re.
• Penetrate the highest part of the roof. This minimizes the
effects of wind turbulence.
• Be located away from trees, adjacent structures, uneven
roof lines and other obstructions.
Offsets can restrict draft so their use should be minimized.
Consider the fi replace location relative to fl oor and ceiling
and attic joists.
Recommended
Location
Marginal
Location
Location
Not
Recommended
Recommended
Location
Multi-level Roofs
Windward
Leeward
Location
Not
Recommended
Figure 2.1 Recommended Chimney Locations
Draft is the pressure difference needed to vent fi replaces
successfully. Considerations for successful draft include:
• Preventing negative pressure.
• Location of fi replace and chimney.
Negative Pressure
Negative pressure results from the imbalance of air avail-
able for the fi replace to operate properly. Causes for this
imbalance 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 (recessed lighting, attic hatch
opening, duct leaks).