What’s a double flue?

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A double flue is two flues routed together out of a structure, used to minimize the number of holes in a roof. It allows for multiple fireplaces or different types of fuel combustion devices to be connected to the same chimney, but special code restrictions apply for safety reasons.

A double flue is a set of two flues that are routed together out of a structure. These types of flues are sometimes fitted into existing fireplaces, and in other cases, a fireplace may be designed from the outset with the intent of being a double flue. For an example of what this type of flue looks like, an analysis of photographs of large villas may provide some examples, as many of these structures use double flue designs to minimize the number of holes in a roof and, as a result, chimney pots are often seen in pairs emerging from the same chimney.

There are a number of reasons for using a double flue. In cases where multiple fireplaces, wood stoves or other heating devices are connected to the same fireplace, that fireplace may not be able to generate enough draft to handle all of these accessories. As a result, lighting a fire upstairs could cause smoke to escape downstairs. In these cases, enclosing a double flue inside the flue allows you to have two fireplaces on separate flues. The design also allows a flue to be plugged to prevent drafts when a room is closed without affecting the function of another device connected to that flue.

A double flue can also be used when two different types of fuel combustion devices are connected to the same flue. For example, someone might use dual fuel to vent an oil stove and a gas stove through the same chimney. Since different fuels burn at different temperatures, causing differences in the temperatures of the fumes they produce, it may be necessary to use separate flues to obtain an adequate draft, or for safety reasons.

The new double flue construction is popular because it gives people flexibility and some additional options. Separate flues can be used to vent a wide variety of fuel burning devices and if a flue becomes unnecessary it can be plugged to minimize drafts and uncovered later in case someone want to use it.

For safety reasons some special code restrictions apply to a double flue design. When designing this type of flue it is important to use a heating specialist who is familiar with flue design and associated codes to confirm that the flue will operate efficiently within the law. If you are modifying an existing flue to create a double flue, a heating professional can help the modification go as smoothly and painlessly as possible.




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