Backdrafting occurs when the combustion gases can't go up and out flues and chimneys because outdoor air is already flowing down them (Fig.
B BACKDRAFTING BACKDRAFTING is a condition in which air flows down a flue or chimney rather than up, and combustion fumes can't flow out.
But if it's a furnace or water heater that's backdrafting, you can be in serious--even deadly--trouble.
Backdrafting is a threat to the health of your family and your house.
Backdrafting became an increasing problem after the energy crisis of 1973 when gas lines and rising fuel prices made energy conservation a high priority.
Fortunately you can easily test your furnace and water heater for backdrafting. Set up a worst-case scenario by closing up your house as you would during cold weather or during hot weather when the air conditioner is running full time.
If the flame or smoke is not drawn to the flue, or is blown away from it, you have a backdrafting problem.
Even replacing a couple of old, leaky windows with new, tight ones can upset the sometimes delicate balance of airflow through your house and cause backdrafting.