What Is A Flue And Why Do You Need One?

What is a Flue?

A flue is a passageway for smoke and fumes to travel through, away from a fire. Most older properties will have a brick chimney to carry smoke and fumes away from the fire. Flues are lined differently depending on whether a fire is wood/coal fired or gas.

Brief History of Flues

Early indoor fires were allowed to billow smoke around inside buildings. This had obvious disadvantages, which led to the creation of the first flues. The first flues were built out of stone, however it was soon discovered that brick flues could withstand higher temperatures, and by the 18th century most flues were made of brick. In more modern times, flues have evolved still further to meet the needs of ever changing heating solutions.

Types of Flue

Chimney – the traditional chimney style flue is still a common sight on most rooftops.

Clearly defined by a chimney stack and a pot, these flues are still made out of brick.

Pre Cast Flue – hollow concrete blocks are used to create a flue up through the property. This is usually topped with a ridge vent up on the roof.

Pre Fabricated Flue – metal flue pipes run up from a metal flue box behind the fire up through the roof.

Power Flue – if there is no way to run a flue up to the roof (you may for instance have a flat above you), then a power flue is one solution. This is where a quiet but powerful electric fan expels the gases through the wall.

Balanced Flue – in a similar fashion to the power flue, the balanced flue vents gases away from the fire out through the wall. Unlike the power flue though, the balanced flue does not require mains electricity. Instead, it uses horizontal twin wall pipes.

Flue Safety

It is of great importance that the right type of flue is used for the fire used. A wood stove should not be connected to a flue pipe that is used to service a gas appliance. This type of flue will have an aluminum lining, and when connected up to a wood stove it will soon corrode or burn out.

If you have a wood fire or stove, remember to get the chimney swept on a regular basis. This prevents the build up of creosote in the lining. A cool chimney (think depths of winter) could allow third degree creosote (sometimes called glaze creosote) to form. This is much denser and more difficult to remove than regular creosote. Creosote is a flammable by product of burning wood. If the creosote is allowed to build up, and the chimney gets hot, it can catch alight and get out of control. Sweeping your chimney on a regular basis will help prevent this. An alternative to sweeping is to have the chimney lined. These days, flue linings made from steel have been developed for use with different fuel type fires. Another option is to pyrolise your chimney. This is the process of deliberately letting your fire get very hot, and burning off the creosote before it can build up too much.