Backdrafting
A condition where combustion gases from a furnace, water heater or fireplace spill back into the living space instead of venting outside.
What is Backdrafting?
Backdrafting occurs when a fuel-burning appliance cannot establish proper draft and its exhaust — which contains carbon monoxide — enters the home. Common causes include a blocked or disconnected vent, an undersized or oversized flue, negative pressure created by exhaust fans or a clothes dryer in a tight house, or a water heater sharing a flue with a newer high-efficiency furnace. Because the consequence is potentially fatal, backdrafting is one of the findings inspectors treat as immediate rather than routine. Testing typically involves closing the house, running exhaust appliances, and checking for spillage at the draft hood after the appliance fires. Any evidence of spillage, scorching or rust streaking at the vent connector deserves prompt evaluation.