B. Negative Pressure
WARNING
Asphyxiation Risk
•Negative pressure can cause spillage of combustion fumes and soot.
•Fire needs to draft properly for safe operation.
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
•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 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 fireplace 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
•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.
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| Recommended | Recommended |
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| Location | |
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| Location |
| Location | Marginal |
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| Location |
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| Not |
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| Recommended |
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| Location |
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| Not |
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| Recommended |
| Windward |
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| Leeward |
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| Figure 2.1 Recommended Chimney Locations |
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6 |
| Heatilator • GB4336/GB4992 • | |