The fireplace is an area many owners overlook when upgrading the energy efficiency of their homes. One of the most important mechanisms in an energy-efficient fireplace is the flue damper. When missing or inoperable in a fireplace, valuable warmth escapes from the firebox in the wrong direction and wood or combustible fireplace products may burn too quickly.
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A flue is a pipe or tube used to carry steam, gas, hot air, fumes or smoke produced by a fire, gas heater or other fuel-burning mechanism away from its source. Sometimes referred to a smokestack or chimney flue, a flue is not a chimney but a separate shaft that sits inside a chimney. The flue prevents the chimney from interior damage caused by the substances it expels -- noxious fumes and particulates, such as soot and embers. Containment by the flue helps direct these caustic substances away from areas inside the house where people, animals and things might otherwise be harmed or damaged by them.
A damper is a mechanism that closes off or silences vibration or substances such as air, flame or water. Merriam-Webster's online dictionary describes a damper as having “a dulling or deadening influence.” The purpose of a damper is to reduce, soften, muffle, mute or end a process, the movement of a process or a substance in a process, such as the vapors generated by a steam engine or the smoke and ash that burning wood creates in a fireplace. In a fireplace, a metal plate is used to create a damper.
The purpose of a flue damper is to reduce the loss of heat in the room -- heat rises and easily escapes up a flue. Once closed, the flue damper retains what heat is left in the firebox and the warmth exits into the room. Flue dampers can be adjusted incrementally to control the speed at which air escapes up the flue; this controls the rate the fire burns.
Once a fireplace burner has turned off, an automatic door attached inside the flue closes. That door is called a flue damper. Fireplaces without a burner have a manual flue damper that requires the user to close it once heat is no longer generated in the fireplace.
Chimneys and flues should be cleaned and maintained seasonally for best results. During warmer months, when the flue damper is closed and the fireplace unused, all manner of debris can collect on top of a closed damper, including nests used by birds or small animals and pests. Cleaning the flue and damper before lighting a fire prevents the igniting of this buildup once the flue is opened for first use in the fall or winter. Catching all the debris piled on top of the closed flue damper requires a large, sturdy bin or bag placed inside the firebox to catch the items as the flue opens.