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A flue pipe is a metal pipe that is run inside of a masonry chimney or run as a stand-alone chimney pipe leading from a furnace or heating stove. The flue pipe carries smoke and noxious fumes out of the living space of a building and vents the fumes into the atmosphere. In some instances, a flue pipe may also be used to exhaust fumes from a cooking stove or grill out of a structure and into the open air outside of the building. In order to maintain a properly working flue pipe, regular cleaning and maintenance must be completed.
In many old masonry chimneys, the tile flues become cracked and broken over time. The effects of repeated heating and cooling cause the clay tiles to become brittle and fragile. As cracks form, heat and soot can fill the cracks, creating hot spots. The hot spots can lead to dangerous chimney fires, which can cause total loss of the structure. Placing a metal flue pipe inside of the broken chimney is often a cost-effective way to avoid such fires.
The sections of flue pipe are assembled and slid down inside the chimney. This gives the chimney a way to exhaust fumes and smoke without the heat ever making contact with the damaged masonry tiles. The original chimney offers protection to the weaker metal flue pipe, and the entire chimney system benefits from the installation. While still requiring regularly scheduled maintenance, the metal flue pipe is much easier to clean due to its smooth interior and very tight joints between sections.
In new construction, a metal flue pipe is often installed within the building's walls and vented to the outside of the building through the roof or wall. While some flue pipes are placed inside of chimney facades, others are run straight out of the roof much like a sewer vent pipe. Typically made of multi-walled pipe, the flue remains cool to the touch on its exterior and promotes no hot spots or fire dangers to the structure. Decorative caps and covers are often used to provide an aesthetic view to the public.
Modern high-efficiency heating systems often require much smaller flue designs than older models. The flue plays an integral part in the performance of the heating unit and is designed to vent a certain amount of fumes out of a structure in a given time period. By controlling the amount of fumes exhausted from the unit, the amount of ambient heat lost through the flue can be calculated and decreased.