The flue is a construction element used to convey smoke from the combustion of different materials and to release them outside the home.

The need to have one depends on the type of heating used and the need to expel smoke and fumes that would otherwise be harmful to persons in the rooms.

It is generally positioned above the combustion chamber and this also applies to fireplaces, but often the configuration of the rooms does not allow a vertical linear positioning for expelling fumes.

We will describe specifically what a flue is and why it is so important.

What is the flue?

As previously mentioned, the flue is a duct that carries smoke outside the building, its correct installation guarantees a perfect draft for a fireplace or stove.

It is composed of two parts, the smoke channel that is the part between the stove or the fireplace and the walls or ceiling of the house, while the flue is the section that reaches the chimney, which is the final part of the flue outside the building, from the ceiling or wall.

The flue can be made of masonry or steel, however, it must be made of materials that are refractory to both heat and fumes that need to be conveyed to the outside.

Why do you need a flue?

Stoves and fireplaces create combustion that generates columns of hot air that rise as smokes and fumes due to their difference in density with the surrounding air. The presence of a well-functioning flue ensures that these exhaust elements are extracted and dispersed into the atmosphere to avoid intoxication of the inhabitants.

Furthermore, the flue or chimney is the combustion engine considering that it guarantees the right supply of air, necessary for the correct functioning of the stove.

It must be specified that for wood or pellet stoves you may not have collective flues, for each duct there must be a dedicated chimney, where other fumes cannot be channelled to avoid overloading and therefore damage.

Why is it so important?

The flue is a crucial component of the heating system and, as we will see later, it is subject to specific standards.

Its perfect functioning must be guaranteed and to facilitate this there are some fundamental characteristics:

• smooth internal walls;
• an almost straight internal path must be provided for the exhaust fumes;
• a chimney that must function properly even during adverse weather events;
• a correct height so that the fumes have no problems of being expelled outside.

A well-built fireplace that periodically receives the right maintenance ensures that the fumes produced by combustion do not remain inside the home, guaranteeing the right supply of air for combustion which otherwise would not occur and, therefore, there would be no way of heating the surrounding environment.

Correct installation of the flue

As you have understood, the correct installation of the flue allows a perfect functioning of the heating system whether it is for a pellet stove or a fireplace.

For the installation to be done correctly, you must first know perfectly where the stove will be placed inside the home. This preliminary study allows you to study a path that is as linear as possible, if this is not possible then you should foresee at most 3 or 4 curves and it will be stable, however, it is best to seek a path that arrives outside that is short enough to make the draft work efficiently.

Whenever the direction is changed, it is necessary to provide a T and condensation collection caps, useful when the stove is lit.

It is better to choose curves and pipes that can be inspected to check them periodically, avoiding any excessive build-up of soot inside the duct.

The flue’s pipes can be made of different materials, we generally recommend porcelain ones resistant to corrosion, scratches and bumps.

For each directional change or for each section where the pipes are joined, there must be fixing brackets that guarantee stability. Furthermore, to avoid fumes leaking between one tube and the other, it is good to place the tube’s female joint upwards and be very careful not to damage the gaskets that serve as insulation for the various tubes.

It is good to specify that both the pipes for wood-burning stoves and those for pellet-burning stoves must be installed by professionals and who know how to do the job in compliance with the regulations we will discuss below, who can also guarantee the post-installation verifications and provide the smoke certificate, with the other documentation released upon completion of each flue’s installation.

Flue draft: perfect cleaning of the flue

For a correct functioning of the heating system, the flue must be maintained periodically cleaning the entire smoke disposal system. Below, we will illustrate the techniques and tools useful for this purpose.

Soot or a physical obstruction can cause a malfunction and self-ignition, bringing high risks for the people inside the house.

There are no universal rules regarding the regularity of cleaning or the methods to use, considering that all flues are not the same, but there are some small tricks that everyone can do daily when using a stove or fireplace.

The first sign to notice to understand if it is time to perform maintenance is to check the heating system’s functioning. The first alarm bells are a fall of soot and the presence of smoke.

For cleaning you can proceed from the top, starting from the chimney or the bottom starting from the inside of the house, from where the pipes enter the wall or from where they go outside.
The tools necessary for cleaning are:

• sramrod – a brush with metal bristles that must be of a length such as to occupy the entire diameter of the tube and therefore clean its walls adequately;
• a rod with adjustable and articulated couplings to adapt to any length of pipes;
• rope and weight when acting from the top to bottom, they are tied to the rod to facilitate the descent into the chimney and its retrieval once the cleaning is finished.

Whether you are cleaning pipes for a wood stove or pipes for a pellet stove, the technique is that of sliding the brush inside the pipe channel to remove any sediment that could cause the stove to malfunction.

If you decide to operate from above, the important steps are those of fixing the ladder to get to the roof and to avoid dirtying the whole environment it will be necessary to seal the pipes’ vent so that soot will not fill the whole house.

Everything we have talked about so far for correct maintenance does not go beyond the fact that both for installation and for cleaning it is good to contact specialised personnel such as installers and chimney sweeps, who can do the job with extreme efficiency and above all in complete safety. These people will have the ideal tools to do the job in the best possible way, without endangering the safety and integrity of people and things.

Flues: the reference legislation

As mentioned in the previous paragraphs, each flue must meet the characteristics imposed by the law to protect anyone who has a heating system at home that includes an external flue.
The main regulatory references which must be followed for fireplaces are:

• • UNI EN 1443: which is the basic standard for the proper functioning of the flue. It is the legislation that conveys all the others and identifies the minimum compliance requirements;
  • UNI EN 1856: this regulation supervises the use of metal pipes which must be insulated and must also have the EU marking to comply with the product standards in force in the European Union market;
  • UNI TS 11278/08: this regulation instead specifies the materials to be used for flues, ducts and chimneys, per the appliance used and the type of installation to be carried out;
  • UNI 10683/12: if previously the discharge of the fumes to the wall was allowed, this legislation required that the expulsion and therefore the dispersion fumes be made on the roof.

The flue’s size and characteristics for stoves and fireplaces

In order for a flue to be considered as built in a workmanlike manner it must comply with certain characteristics, many of which we have seen in the course of our text, others in the following.

The flue’s height and size of the chimney must be such as to guarantee a perfect draft therefore it must be commensurate with the pipes for a pellet or wood stove. Its course must be vertical and avoid changes of direction as much as possible, the internal walls must be smooth and insulated to be heat resistant. It is good to opt for circular sections. If you need them to be square or rectangular they must have rounded corners to allow the fumes to flow better.

The curves used must not exceed 45 degrees and remember that to be efficient, the flue’s length must be as short as possible.

Installing a flue in an apartment building

If you decide to install a flue inside an apartment building you will need to pay attention to certain details. Meanwhile, the condominium regulations need to be consulted in the implementation of the works especially for the part that concerns the common areas, also verify that there are no impediments to third parties.

The work must not adversely affect the property of others by affecting their right of view and it is also necessary to comply with the minimum distances’ rules imposed by the various municipalities.