Flue design involves the structure of a vertical chimney that discharges hot air from a heat source. Design choices include inside or outside a building, and can be modified to support multiple heat sources. Flue designs can be open, balanced, or vented, and can be retrofitted with a flue kit.
Flue design refers to the structure of a vertical chimney that discharges hot air as a by-product of combustion into a stove, fireplace, boiler, or other heat-producing system. Design choices for flues are inside or outside a building and can be modified to support more than one heat source or lined to downsize an existing chimney. Airflows in a flue design include those that use natural vents and those supported by a blower or blower.
The simplest type of flue design is an internal vertical pipe or channel that runs directly from the heat source through the roof of the building. In residential situations, the chimney must be insulated wherever it meets walls or ceilings to protect these structural components from the chimney’s high temperatures. For safety, flues are often lined throughout. The point where the chimney meets the roof of the building must be carefully sealed from the outside against the elements.
To accommodate two different heat sources and have only one opening in the roof, it is possible to create a double flue. The vertical space of the flue is divided into two separate channels, allowing the exhaust of the two heat sources to vent independently. This configuration can also vent exhaust from heat sources to several floors of a building.
An outside flue can lead from the heat source directly outside and then flow vertically the rest of its height. This flue design can be less efficient because the entire flue is exposed to cooler outside air. Joining the heat source to the flue and avoiding the gutter to the roofline requires the use of angled connections at an angle of no more than 45 degrees from the vertical. These joints may require more frequent cleaning due to increased soot buildup in the bends.
To retrofit an existing flue for a new heat source, a flue kit can be a good flue design solution. The flue kit includes sheet metal pipes which can be cut to fit, assemble and use within your existing chimney. This solution is generally simpler and cheaper than building a completely new chimney.
A flue design can be open, balanced, or vented. A system that uses only natural ventilation is an open system. A balanced system is one where the heat source does not draw in air from its surroundings, but is sealed and has its own vent or air source. In a hermetically sealed modern house, where no air from outside enters, the movement of air to the chimney can be prevented if the heat source does not have an independent air supply. A ventilated system incorporates a fan, transforming it into a forced draft system, which ensures the supply of air to the heat source and the movement of air upwards towards the flue.
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