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B. Negative Pressure
WARNING
Asphyxiation
Risk.
Negative pressure can cause spillage of
•
combustion fumes and soot.
• Fireplace needs to draft properly for safety.
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 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 heat-
ers and other combustion appliances
• Clothes dryers
• Location of return-air to furnace or air conditioning
• Imbalances of the HVAC air handling system
• Upper level air leaks (recessed lighting, attic hatch
opening, duct leaks)
To minimize the effects of negative air pressure, the fol-
lowing must be considered:
Location
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W indw ard
Figure 2.1
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Location
M argin al
Location
N o t
Heat & Glo • SL-550 / 750 / 950TV-IPI-E • 2119-900 Rev. G • 9/08
• Install the fresh 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 combus-
tion 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 of "sealed can" design;
attic hatches weather stripped or sealed; and attic
mounted ductwork 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 perfor-
mance. As shown in Figure 2.1, the chimney should:
• Be installed through the warm space 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, un-
even 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.
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Location
Location N O T
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M u lti-level R o o fs
Leew ard
7
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