How does a fireplace flue work?

Fireplace flue principle and updraft

Fireplace flue can generally be divided into: metal pipe, ceramic pipe or brick chimney. Connecting from the back of the fireplace and extending into the outer space, the flue channels the exhaust gas and debris from the fireplace upward to the outside and into the outside air. The flue is effective because it takes advantage of the chimney effect that occurs when there is a significant temperature difference between the indoor and outdoor ends of the flue.

This effect can draw exhaust gases and soot, which are lighter than cold air outside, into the fireplace flue and discharge them to the outside. Some heat is also lost during this process, and sometimes some changes can be made in the fireplace furnace or above the furnace to minimize this loss of auxiliary heat.

Fresh air is drawn in from the outside to supply the fire

The second purpose of the flue is to allow fresh air to be drawn in from the outside, helping to supply the fireplace with oxygen needed for combustion. At one end of the fireplace, where the flue is connected, is a lever-operated damper device that can be opened when the fireplace is running to allow exhaust gases from the furnace to escape and fresh air from outside to enter. When the fireplace is not in use, the control lever can be turned off to prevent cold air from entering the home.

Troubleshoot the fireplace flue
Flue problems may make the fireplace operate inefficiently or hinder the effectiveness of pumping and normal exhaust work. If your fireplace emits smoke while it is burning, and the damper is now fully open, the flue may become blocked by soot, creosote residue, trapped animals, and even bird nests.

If there is smoke backfilling in the room, it is best to hire professional chimney cleaning. If this happens occasionally in the fireplace, make sure the damper is in the fully open position. It may be stuck in a half-open position or the lever arm is damaged, in which case you need to make a fireplace chimney repair or replace it.

Another problem may be insufficient pumping. If the top of the flue is not exposed to enough air, whether it is trees or shrubs gathering around the flue outlet, or the addition of buildings changes the air flow around the flue, even subtle airflow restrictions can significantly alter the fireplace flue function. This can usually be solved by increasing the chimney exhaust fan or increasing the length of the fireplace flue.