In my recent article, “Hidden Problems Can Cause Carbon Monoxide”(The News, October 10, page 10), I discussed, among other things, the combustion air system. This system is made up of the venting to the furnace enclosure, which allows fresh air to be drawn from the outside of the structure to the inlet of the heat exchanger; the heat exchanger itself; and the flue system, which allows the combustion products being generated by the furnace to exit the structure to the outside. In this article, I’d like to cover more about the discharge side of the combustion air system, the flue.
The natural pressure differential created by heating the combustion gases in the furnace is what pushes the flue gases up and out of the flue.