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Hearth & Home Technologies • BV4236DBI, BV4842DBI • 2209-900 Rev. P • 4/14
Figure 4.2
E. 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
available 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 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:
• 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 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 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 4.2, 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, 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
Location NOT
Recommended
Multi-level Roofs
Windward
Leeward
