CHIMNEYS – repair method

When we mention chimneys, we usually first think of the brick / stone chimneys on family homes. Smoke comes out at the top of the chimney, and a fire burns in the fireplace.

Today, in most cities, a gas boiler is connected to the chimney, which is used for heating and preparing hot water, or a gas storage furnace.

When installed in a new facility, heating devices using gas, solid, or other type of fuel, it is also necessary to provide for a flue gas drain. The mechanical installation project will provide for next-generation devices. Accordingly, adequate chimneys will also be provided.

If the building is being reconstructed and that the old appliances need to be replaced with new ones, it is often necessary to carry out the chimney replacement, that is, to carry out its "repair".

Principle of operation

Old devices that are still in use, known as "façade" or "atmospheric", will need to be replaced in due course. Old devices took combustion air from the premises, and flue gases were released through the façade or roof chimney. Old devices are no longer allowed to be installed. In the last few years, "turbo" boilers have been installed, which also have a flue gas fan.

New devices, known as "condensing", take combustion air off-site, and flue gases are released through the chimney on the roof. Flue gas discharge is not allowed on the façade except in special cases. For new devices, it is necessary to provide, in addition to the flue gas exhaust, the combustion air supply. "Turbo" boilers have a similar principle of operation.

Chimney "repair"

When you hear the term "repair", you often think of everything, and it is simply necessary to repair the chimney if it is defective or to adapt it to a new boiler.

If you change the boiler from " façade" to "condensing" one, it is necessary to carry out the chimney "repair".

The first step in the "repair" process is an inspection of the local chimney sweep, who will give a report on the condition of the chimney, and from which it will be visible how the chimney "repair" can be carried out.

In some cases, it will also be necessary to develop a project for it.

In the following few examples, simplified chimney schemes are given, offering you an indicative idea of the possible ways of carrying out the chimney "repair", noting that before each repair it is necessary to request a report from the local chimney sweep on the condition of the chimney and the possibility of its repair, and that the installed equipment must be attested, have the prescribed documentation and be installed by professional staff.

Option 1

We use the existing chimney only as a construction shaft through which we pass the flue pipes for the supply of air to the boiler and the discharge of flue gases (Figure 1). Depending on the boiler type we are installing, the horizontal distance from the chimney and the vertical height of the chimney must be considered. Certified chimneys, depending on the manufacturer, allow a horizontal distance of up to 3 m', and a vertical height of more than 12 m'. If we have other parameters, it is obligatory to ask the suppliers for a chimney calculation from which it is visible that they meet the specified conditions.

Slika 1 - Dovod zraka sa krova

Slika 2 - Dovod zraka iz okna

Option 2

We use the existing chimney as a construction shaft through which we run the flue pipe for flue gas discharge. Only the construction shaft serves us to supply combustion air (Figure 2).

Option 3

In case we are not able to bring combustion air through the construction shaft, or through pipes from the roof of the building, there is also the possibility of bringing air through separate pipes from the building’s façade (Figure 3).

Slika 3 - Dovod zraka sa fasade

Other options

In addition to the aforementioned possibilities and, depending on the place of installation of the boiler, it is possible to pull the chimney along the façade or, if it is in the attic, directly through the flat/sloping roof (Figure 5). If the chimney goes along the façade, then the intake can be from the roof of the building or from its side (Figure 4).

Slika 4 – Vođenje po fasadi


Slika 5 – Prodor kroz krov


The above examples are given for cases where “repair” is carried out through straight chimneys with rigid pipes. In case the chimney is not straight, the "repair" can be carried out with flexible pipes (Figure 6). It is necessary to pay attention to the combustion air supply method.

Older buildings are most often constructed in such a way that each apartment has its own chimney, so that "repair" is possible even without affecting other chimneys in the building.

If more than one boiler is connected to the existing chimney, then it is necessary to carry out a joint repair by connecting it to one flue pipe (Figure 7) or to check another possibility with the chimney sweep.

Slika 6 – Sanacija fleksibilnom cijevi

Slika 7 – Više bojlera

All the above-mentioned repair options are given with a simplified chimney display scheme. The exact appearance of the chimney, flue and other parts depends on the boiler type to be installed, the required chimney height and the place of installation.

Usually, boiler manufacturers also offer certified chimneys for the selected device. If this is not possible, the chimney supplier should confirm the correctness of the selection decision with a satisfactory calculation


      • Before making any decision, request a report from a local chimney sweep on the condition of the chimney.
      • Use the services of authorized contractors to install the chimney.
      • Only install certified products i.e., equipment confirmed by the project.
      • Before putting the device back into operation, it is necessary to obtain a chimney sweep's certificate