Back-Drafting

Safety - Home Energy and Building Envelope pillar

Also known as: backdrafting, back drafting

When negative house pressure pulls combustion gases (including CO) back down a chimney into the living space instead of out through the vent.

Back-drafting occurs when a depressurized house pulls combustion gases from an atmospheric-vented gas appliance (water heater, older furnace, fireplace) back down the chimney into the home. Causes include large exhaust fans (kitchen range hoods over 400 CFM, dryers, central vacuums) running while combustion appliances fire, very tight envelopes without designed make-up air, and blocked or undersized vents. Back-drafting is the leading cause of CO poisoning incidents in Ontario homes. Mitigation: dedicated make-up air, sealed-combustion appliances, atmospheric-to-power-vent conversion.

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