FR3011316A1 - METHOD FOR RENOVATING BOILER EXHAUST DUCTS - Google Patents

Abstract

A method of renovating boiler exhaust ducts (1), the exhaust duct (1) comprising an inner pipe (20) and a chimney pipe (10), the inner pipe (30) being connected to at least one the exhaust pipe (32) and the outer pipe (20) being connected to at least one combustion air connection pipe (22) which surrounds the exhaust gas connection pipe (32), the method comprising the steps of: (a) introducing a cutting tool (40, 42) into the combustion air connection pipe (22); (b) cutting the exhaust gas connection pipe (32) from the inner pipe (30) by means of the cutting tool (40, 42); (c) removing the cut exhaust gas pipe (32), an opening (34) remaining in the inner pipe (30); and (d) inserting a plastic exhaust pipe (50, 52) through the opening (34) into the inner pipe (30).

Description

The present invention relates to a method of renovating boiler exhaust ducts, particularly exhaust ducts in multi-storey buildings that always have a stainless steel or aluminum exhaust duct. The present invention is applicable especially during a restructuring of the heating system according to the technology of the heating power. Today, many existing buildings, especially multi-storey buildings, are equipped with old-fashioned boilers that cause a lot of energy loss. During a renovation of the heating system, these old-fashioned boilers are replaced by modern condensing boilers using heat-power technology. These oil-fired condensing boilers or heating heaters are distinguished by improved energy efficiency, but they necessarily have a very low exhaust gas temperature. Therefore, when replacing the boiler, the boiler exhaust duct must generally be renovated, as the existing boiler exhaust ducts are not suitable for the low exhaust gas temperature. and condensing the exhaust gas into the resulting exhaust conduit. Especially multi-storey apartment buildings are often equipped with a multi-storey gas heating system, where multi-storey heaters are connected to a common vent. The supply of air to the heaters is often effected by an air channel or an aeration slot in the common exhaust duct. Such boiler exhaust ducts are, as a general rule, removed completely from the building in the event of renovation to utilize the heat-power technology and replaced by a modern plastic exhaust and vent system. Such an exchange of the evacuation duct requires a considerable construction effort and results in an exposure of the inhabitants of the building to debris and dust which may last several weeks. During this time, a temporary supply of hot water and heating for the inhabitants must be put in place, if the building is inhabited during the renovation. Overall, an exchange of the boiler exhaust duct also entails considerable costs. The present invention therefore aims to set up a boiler exhaust ducts renovation process that can be performed faster and with less effort of construction and is more economical and causes only a minimum of trouble for the locals. The present invention proposes, in addition, to be able to perform the renovation so quickly that a temporary supply of heat for hot water and for heating is not necessary.

The aforementioned problems are solved by a method of renovating boiler exhaust ducts in which the exhaust duct comprises an inner pipe, an outer pipe and a chimney pipe, the inner pipe being connected to at least one pipe exhaust connection pipe and the outer pipe being connected to at least one flue gas connection pipe surrounding the exhaust gas connection pipe, the method comprising the following steps: a. introducing a cutting tool into the combustion air connection pipe; b. cutting the exhaust pipe of the inner pipe (30) by means of the cutting tool; vs. removal of the exhaust gas connection pipe cut off, an opening remaining in the inner pipe; and D. insertion of a plastic exhaust pipe through the opening in the inner pipe. With this method, the previous vent pipe does not need to be dismantled or demolished completely, but it can remain largely in the building. In order to use modern condensing boilers or heating heaters, plastic pipes for exhausting the exhaust gas are introduced by reticulation into the exhaust duct. The inner pipe, which had been used as the exhaust pipe in the original exhaust pipe, is no longer in contact with the exhaust gas and can, instead, drive the supplied air which is preheated to heating heaters. The outer pipe that also carries supply air may remain unchanged and may continue to perform this task as well. In order to set up the plastic exhaust pipes, the invention only provides for a cutting tool to be introduced into the combustion air connection pipe and, with the aid of this, here, the exhaust gas connection pipe is cut from the inner pipe. After removal of the exhaust connection pipe, there remains an opening in the inner pipe through which the new plastic exhaust pipe can be introduced.

The method according to the invention can be carried out very quickly and in an easy way, and it requires only a very small construction effort. There are no large amounts of sludge or even excavation if the process is carried out in accordance with the invention, unlike the methods of the state of the art. The troubles for the inhabitants are therefore reduced to a minimum.

Because of the rapidity of the process according to the invention, the exchange of several heaters, for example from four to six, and the renovation of the exhaust duct system can be done simultaneously in one day, so that a temporary supply of heat for hot water and heating is not necessary. The process according to the invention therefore has immense cost advantages compared to the processes of the state of the art. Preferably, the cutting tool is introduced into an air gap between the combustion air connection pipe and the exhaust gas connection pipe. By this, the combustion air connection pipe is not damaged and the exhaust connection pipe is cut only to the inner pipe, so that the cutting force is minimized. The exhaust connection pipe can be removed as a whole. Other cutting operations are not necessary.

In another embodiment, the cutting tool is introduced into the exhaust gas connection pipe. This embodiment is suitable when a cutting tool which is too large to be introduced into the ventilation slot between the combustion gas connection pipe and the exhaust gas connection pipe is to be used.

In one embodiment, the cutting tool is an entrance saw. An entry saw can be easily inserted into the ventilation slot between the combustion air connection pipe and the exhaust gas connection pipe and can cut the exhaust gas connection pipe in its entirety. with minimal cutting volume. In addition, an entry saw produces a clean, round opening in the inner pipe, making it easier to insert the plastic exhaust pipe. Preferably, the diameter of the inlet saw is larger than the outside diameter of the exhaust gas connection pipe and smaller than the inside diameter of the combustion air connection pipe. In order to achieve as much opening as possible in the inner pipe, the diameter of the entrance saw is preferably chosen as large as possible. The maximum size of the diameter of the inlet saw is delimited by the inside diameter of the combustion air connection pipe. According to another embodiment, the cutting tool is a plasma fusion cutting tool. A plasma melting tool produces a very hot plasma which melts the material of the inner pipe locally and can thus be used, without deployment of force, to cut the exhaust pipe of the inner pipe. A plasma fusion cutting tool is particularly suitable for an inner pipe made of either stainless steel or aluminum. With a plasma cutting tool, the cutting is done very quickly also in case of thick material thicknesses. For thick material thicknesses, a plasma fusion cutting tool therefore has speed advantages compared to an input saw. The disadvantage is that the cutting edges are not very sharp. Preferably, when cutting according to step b., An earth ground of the plasma melting tool is connected to the exhaust gas connection pipe. The earth connection can be made without problem at the exhaust connection pipe. In another embodiment, the cutting tool is a grinding wheel. By means of a cut-off wheel, which is preferably operated by a straight grinder, the exhaust gas connection pipe can be cut from the inside. To do this, several sheared cuts may be necessary. This embodiment is particularly suitable for a steel exhaust connection pipe which can be easily cut with a suitable cutting wheel.

Preferably, the method further comprises the step of enlarging the opening in the inner pipe. Through a larger opening in the inner pipe, the plastic exhaust pipe is more easily introduced into the inner pipe. This process step is particularly advantageous if the exhaust gas connection pipe has been cut by means of a cut-off grinder. Preferably, a nibbler [German: "Knabber"] is used to enlarge the opening in the inner pipe. A nibbler, which is referred to as "Nibbler" or "Nager" in German, is a tool for working the sheet comprising a cutter tool consisting of a punch and a die. The punch that is actuated by a motor moves up and down in the die and thus cuts a part of the workpiece, for example, from a sheet metal pipe. A nibbler therefore punches a cutting trace by producing knockouts punching. One of the advantages of a nibbler is the separation of metal sheets without distortion. Preferably, a nibbler is electrically operated. Also cordless nibblers powered by accumulator. Preferably, the opening in the inner pipe has a diameter which is larger than that of the exhaust gas connection pipe.

The opening remaining in the inner pipe after cutting has a diameter which is larger than that of the exhaust gas connection pipe removed, so that the introduction of the plastic exhaust pipe is facilitated. . It is advantageous to cut the opening as large as possible.

Preferably, the flue gas connection pipe is not damaged, so that it can be used as a flue gas connection pipe for a heating capacity heating apparatus also after the renovation. Preferably, the method also comprises a step of shortening the flue gas connection pipe. Preferably, the method also comprises a step of mounting a wall shutter to the chimney flue. If the flue gas connection pipe is shortened so that it is flush with the outer wall of the chimney flue, a wall shutter can be easily mounted forming a clean screed of the flue gas connection pipe. with the chimney. At this wall shutter, the flue gas connection of the modern condensing boiler or the heating capacity heater can be connected for operation independent of the ambient air.

Preferably, the inner pipe is either stainless steel or aluminum or another mineral material. In the case of an inner pipe of mineral material, it is not possible to use a plasma melting tool; it is for this reason that, in such a case, an input saw is used.

Preferably, the outer pipe is a metal pipe stapled sheet metal. This type of pipe is particularly suitable for supplying combustion air to a heating capacity heating apparatus. Preferably, the boiler exhaust duct extends over several floors of a building and includes a plurality of combustion air connection pipes and exhaust gas connection pipes, the steps a. to d. being executed several times. Because of its advantages described above, the method according to the invention is particularly suitable for multi-storey buildings. As a rule, a renovation of four to six individual floor heaters, for example, can be carried out in one day using the method according to the invention. Preferably, the exhaust duct comprises a plurality of flexible plastic exhaust pipes which are all arranged within the inner pipe. Each self-heating heating unit is connected to a single plastic exhaust pipe which, inside the inner pipe, is ducted upwards to the edge of the exhaust duct. . As a result, heating heaters do not interfere with each other.

In the Figures, preferred embodiments of the present invention are reproduced which show: FIG. Fig. 1 is a horizontal cross-sectional view of a preferred embodiment of a boiler exhaust duct prior to retrofit, with a first embodiment of the cutting tool; Fig. 2: a horizontal cross-sectional view of the exhaust duct of FIG. 1 with the first embodiment of a cutting tool during a cutting operation; Fig. 3: a horizontal cross-sectional view of the exhaust duct of FIG. 1 with the second embodiment of a cutting tool, during a cutting operation; Fig. 4: a horizontal cross-sectional view of the exhaust duct of FIG. 1 after the cutting operation, when removing the exhaust gas connection pipe; Fig. 5: a horizontal cross-sectional view of the exhaust duct of FIG. 1 after the introduction of a plastic exhaust pipe; Fig. 6: a horizontal cross-sectional view of a preferred embodiment of a discharge duct before the renovation with a third embodiment of a cutting tool, during a cutting operation; Fig. 7 is a cross-sectional horizontal view of FIG. 6 with the third embodiment of a cutting tool in the shortening operation of the combustion air connection pipe, FIG. 8: a horizontal cross-sectional view of FIG. 6 with the third embodiment of a cutting tool in another cutting operation; Fig. 9: a horizontal cross-sectional view of the exhaust duct of FIG. 6 with a nibbler during the operation of enlarging the opening in the inner pipe; Fig. 10: a horizontal cross-sectional view of the exhaust duct of FIG. 6 after mounting a wall shutter; Fig. 11: a horizontal cross-sectional view of the exhaust duct of FIG. 6 after the introduction of a plastic exhaust pipe into the inner pipe; Fig. 12: a horizontal cross-sectional view of another embodiment of a discharge duct with the third embodiment of a cutting tool in a cutting operation; Fig. 13: a horizontal cross-sectional view of the exhaust duct of FIG. 12 with the third embodiment of a cutting tool during the shortening operation of the combustion air connection pipe; Fig. 14: a horizontal cross-sectional view of the exhaust duct of FIG. 12 with a nibbler during the operation of enlarging the opening in the inner pipe Fig. 15: a horizontal cross sectional view of the exhaust duct of FIG. 12 after mounting a wall shutter; and 16: a horizontal cross-sectional view of the exhaust duct of FIG. 12 after the introduction of a plastic exhaust pipe into the inner pipe. In the following, preferred embodiments of the present invention are described with reference to the Figures. The characteristics of individual embodiments may be combined with features of other embodiments, even if not shown in detail. Figure 1 shows a horizontal cross-sectional view of a preferred embodiment of an exhaust duct 1 prior to refurbishment. The vent pipe includes an inner pipe 30 which at the beginning was used to evacuate the flue gases. The inner pipe 30 is either stainless steel or aluminum or fire clay, said pipe having an exemplary diameter of 315 mm. To connect boilers or heaters which are not shown, exhaust gas connection pipes 32 are connected to the inner pipe in which the heaters had passed its exhaust gases previously. The exhaust duct 1 may extend over several floors of a building where, on each floor, a heater may be connected to the same exhaust duct 1. The exhaust connection pipes 32 are made as a rule, of the same material as the inner pipe 30 and have an exemplary diameter of 80 mm. The inner pipe 30 is arranged concentrically within an outer pipe 20 for supplying combustion air to the heaters. Thus, an air vent 24 for the combustion air is formed between the outer pipe 20 and the inner pipe 30. To supply the combustion air to the respective heating apparatus, combustion air connection pipes 22 are connected to the outer pipe 20 surrounding the exhaust gas connection pipes 32 in a concentric manner. The outer pipe 20 is preferably a stapled metal pipe of galvanized steel sheet with an exemplary diameter of 500 mm. In general, the flue gas connection pipes 22 which may have an exemplary diameter of 125 mm are made of the same material. The outer pipe 20 and the inner pipe 30, in turn, are arranged concentrically in a chimney pipe 10 made of a mineral material which, as a rule, is masonry and, in the example, has the form of a square and can have a length taken in the work of 570 mm. In this case, the combustion air connection pipes 22 pass through an opening of the evacuation duct 12 and project from the evacuation duct 10. In a first step of the evacuation duct renovation process 1 a cutting tool 40, 42 is introduced inside the combustion air connection pipe 22. In the first embodiment shown in Figures 1 and 2, the cutting tool 40, 42 is an entrance saw 40. The diameter of the inlet saw 40 is larger than the diameter of the exhaust connection pipe 32 and smaller than the inside diameter of the combustion air connection pipe 22. The saw The inlet 40 is thus introduced into the ventilation slot 60 between the combustion air connection pipe 22 and the exhaust gas connection pipe 32 until it reaches the inner pipe 30. The diameter of the input saw 40 is preferably chosen as large as pos However, the inlet saw must not damage the combustion air connection pipe 22. Figure 2 shows the second step, the cutting of the exhaust pipe connection pipe 32 of the inner pipe 30 by means of the tool 40, 42. In the case shown, the input saw 40 is rotated by means of a rotating tool, for example a hand drill. Thus, the cutting teeth arranged at the tip of the input saw 40 cut into the wall of the inner pipe 30. By the appropriate choice of the material of the cutting teeth, the input saw 40 can be adapted to the material of the pipe In the case of stainless steel or aluminum, the cutting teeth are preferably of hard metal or of a ceramic removable plate. If the inner pipe 30 is of a mineral material, for example, of fire clay, the cutting teeth may be diamond-shaped. The inlet saw 40, after cutting the exhaust gas connection pipe 32 from the inner pipe 30, must be removed from the combustion air connection pipe 22. FIG. 3 shows another preferred embodiment of the invention. second step of the process. Here, a plasma fusion cutting tool 42 is used to cut the exhaust gas connection pipe 32 from the inner pipe 30. Said plasma fusion cutting tool is also introduced into the ventilation slot 60 between the combustion air connection pipe 22 and the exhaust gas connection pipe 32, until it reaches the inner pipe 30. A plasma fusion cutting tool 42 produces very hot plasma at its tip, this plasma melts the inner pipe 30 locally and the wafer. In order to cut the exhaust connection pipe 32 completely from the inner pipe 30, the plasma fusion cutting tool 42 is conducted once around the exhaust gas connection pipe 32 into the ventilation slot 60 The plasma fusion cutting tool 42 further comprises a base device 46 for generating the voltage required for the plasma, and a grounding plug 44 which is connected in the form of a ground terminal to the pipe. The plasma melting cutter 42 may be used for all metallic materials of the inner pipe 30, for example for stainless steel or aluminum, and may cut such materials. in a quick and easy way also in case of thick material thickness. Figure 4 shows the third step, namely the removal of the exhaust connection pipe 32, as indicated by the arrow 36. After the removal, an opening 34 remains in the inner pipe 30.

In a fourth step, a plastic exhaust pipe 50 is then introduced into the inner pipe 30 through this opening 34 and the remaining combustion air connection pipe 22. This insertion can be done from outside passing through the combustion air connection pipe 22 or from the top through the inner pipe 30. FIG. 5 shows the situation after the insertion of the exhaust pipe into plastic 50 in the inner pipe 30 and after the completion of the renovation of the exhaust pipe 1 relating to a connection point of a heater. Preferably, the plastic exhaust pipe is of an acid-resistant plastics material such as, for example, PVDF, which is therefore suitable for modern calorific appliances having high temperature gas temperatures. low exhaust. The plastic exhaust pipe 50 may be composed of firm tubular elements and elbows, as shown in FIG. 5. Exemplary, the inner diameter of the plastic exhaust pipe 50 is 80.degree. mm. In addition, the plastic exhaust pipe 50 may comprise a flexible plastic exhaust pipe, especially in the region within the inner pipe 30 now used as the combustion air pipe. A flexible plastic exhaust pipe 52 has the advantage of a more flexible mounting in the event of construction tolerances and better heat transfer to the combustion air as compared to a rigid pipe. In Figures 6-12, another preferred embodiment of the exhaust duct renovation method according to the invention is shown. In this embodiment, the inner pipe 30 also has a diameter of 315 mm, and the outer pipe 20 has a diameter of 500 mm. In this embodiment, the combustion air connection pipe 22 has a diameter which is preferably 125 mm, and the exhaust gas connection pipe 32 has a diameter which is preferably 80 mm.

In this embodiment, the cutting tool used is a cut-off wheel 48 actuated by means of a suitable machine, for example a straight grinder 49. For this, the electric straight grinder 49 shown in FIG. 6 is particularly suitable. By its slender shape, and thanks to a small diameter of the grinder wheel 48, the latter can be introduced deep into the exhaust gas connection pipe 32. Then, the exhaust gas connection pipe 32 is cut by means of the cutting wheel 48. The cutting of the exhaust gas connecting pipe 32 can be carried out either by a single cutting operation or by two or more cutting operations using the grinding wheel 48. As shown in FIG. Figure 6, a portion of the exhaust gas connection pipe 32 may be cut. After cutting, the part of the exhaust connection pipe 32 is removed. Then, as shown in FIG. 7, the combustion air connection pipe 22 is cut, preferably, flush with the outer wall of the chimney flue 10. For this purpose, the grinding wheel 48 can also be used on However, the section of the combustion air connection pipe 22 can also be made before the first cutting of the exhaust gas connection pipe 32. Then, as shown in FIG. 8, the remaining part of the exhaust connection pipe 32 is cut out. The opening 34 thus created in the inner pipe 30 can then, as shown in Figure 9, be enlarged if necessary. To do this, a nibbler 70 is preferably used which is capable of working well the material of the inner pipe 30. By enlarging the opening 34, the exhaust pipe 50, 52 can be introduced more easily afterwards. After enlarging the opening 34, a wall shutter 80 is mounted to the flue 10, said wall shutter covering the junction between the combustion air connection pipe 32 and the chimney flue 10. This shutter wall 80 is also used for connecting the combustion air of the new condensing boiler or the new heating capacity heating apparatus to the remaining combustion air connection pipe 22. Figure 10 shows the wall shutter 80 already mounted to the flue 10. Finally, the plastic exhaust air pipe 50, 52 is introduced through the opening 34 into the inner pipe 30. For this purpose , a flexible plastic exhaust pipe 52 is lowered from the top opening of the chimney into the inner pipe 30 until it reaches the height of the opening 34 in the inner pipe. Then, the bottom end of the flexible plastic exhaust pipe 52 is exhausted from the exhaust duct 1 through the opening 34 and the combustion air connection pipe 22. Now, the bottom end of the Flexible plastic exhaust pipe 52 may be connected to a plastic exhaust pipe 50 which is preferably rigid and has a 90 ° elbow. After the connection, the flexible plastic exhaust pipe 52 is pushed back into the inner pipe 30, so that the rigid exhaust pipe extends through the opening 34 and the wall shutter 80. Since the installation of the exhaust gas pipe 50, 52 is thus finished, the latter can serve as a connection for the new condensing boiler or the new heat-energy heating device. Figure 11 shows the exhaust duct 1 after completion of the renovation with the plastic exhaust pipe 50, 52 already fitted. Figures 13-16 show another preferred embodiment of the process for renovating boiler exhaust ducts 1 according to the invention. This embodiment differs from the embodiment shown in FIGS. 912 by the fact that the method is carried out on an evacuation duct 1 with smaller dimensions. In this embodiment, the inner pipe 30 has a diameter of only 200 mm, and the outer pipe has a diameter of 380 mm. In this embodiment, the combustion air connection pipe 22 has a diameter which is preferably 100 mm, and the exhaust gas connection pipe 32 has a diameter which is preferably 60 mm.

As can be seen from FIG. 12, in this embodiment, the exhaust gas connection pipe 32 can be cut from the inner pipe 30 by a single cut by means of the cut-off wheel 48. Then, again here, the air connection pipe 22 is shortened, so that it is flush with the outer wall of the flue 10, so that a wall shutter 80 can be mounted thereafter. Then, the opening 34 in the inner pipe 30 is enlarged by means of a nibbler, as shown in FIG. 14.

Subsequently, the wall shutter 80 can be mounted between the chimney duct 10 and the combustion air connection pipe 22, as shown in FIG. 15. Finally, as shown in embodiment 9-12, a pipe The exhaust gas pipe 50, 52 is introduced through the opening 34 into the inner pipe 30. The completely assembled exhaust pipe 1 is shown in FIG. 16. The new condensing boiler or the new water heater Heating with heat output can then be connected independently of the ambient air. The different steps of the preferred embodiments can be combined with each other. Thus, for example, the opening 34 of the embodiments of Figure 1-5 can also be enlarged and / or the combustion air connection pipe 22 can be cut in order to mount a wall shutter 80. As can be seen from the various embodiments, the method according to the invention is suitable for the renovation of boiler exhaust ducts 1, that is to say, ducts 1 of different materials, sizes, diameters, wall thicknesses and superstructures. . The process according to the invention is particularly suitable for the renovation of boiler exhaust ducts in multi-storey residential buildings equipped with individual floor heating installations. In these cases, an individual plastic exhaust pipe 50 is provided for each heat output heater, i.e., as a rule, for each stage. In the inner pipe 30, all the plastic exhaust pipes 50, 52 are led upwards to the edge of the exhaust pipe and attached thereto. The inner pipe 30 is quite large in cross-section for all the plastic exhaust pipes 50, 52 required for the renovated exhaust pipe 1. In the remaining space between the plastic exhaust pipes 50, 52, even all the necessary combustion air could be conducted inside the inner pipe 30 after the renovation, so that the annular gap enters the inner pipe 30 and the outer pipe 20 can be used also for other purposes, for example to evacuate the ambient air. Through the flow of combustion air around the plastic exhaust pipes 50, 52, the heat is transmitted from the exhaust gases to the combustion air according to the principle of a reverse current heat exchanger. Thus, the combustion air is preheated, which comprises an energy gain. List of order numbers 1 vent pipe 10 chimney flue 12 chimney flue opening outside pipe 22 combustion air connection pipe 24 vent slot for combustion air supply 20 30 inner pipe 32 pipe exhaust gas connection 34 opening in the inner pipe 36 arrow to indicate the direction of removal 40 cutting tool, input saw 42 cutting tool, plasma melting tool 44 earth electrode 46 basic device Plasma cutting tool 48 Grinder wheel 49 Straight grinder 50 Plastic exhaust pipe 52 Flexible plastic exhaust pipe 60 Ventilation slot 70 Nibbler 80 Wall shutter

Claims (21)

REVENDICATIONS1. A method of renovating boiler exhaust ducts (1), the exhaust duct (1) comprising an inner pipe (30), an outer pipe (20) and a chimney pipe (10), the inner pipe (30) ) being connected to at least one exhaust gas connection pipe (32) and the outer pipe (20) being connected to at least one combustion air connection pipe (22) which surrounds the exhaust gas (32), the method comprising the steps of: a. introducing a cutting tool (40, 42) into the combustion air pipe (22); b. cutting the exhaust gas connection pipe (32) from the inner pipe (30) by means of the cutting tool (40, 42); vs. removing the cut exhaust gas pipe (32), an opening (34) remaining in the inner pipe (30); and D. inserting a plastic exhaust pipe (50, 52) through the opening (34) into the inner pipe (30). 2. Method according to claim 1, characterized in that the cutting tool (40, 42) is introduced into an air gap (60) between the combustion air connection pipe (22) and the combustion pipe. exhaust gas connection (32). 3. Method according to claim 1, characterized in that the cutting tool (48) is introduced into the exhaust gas connection pipe (32). 4. Method according to one of claims 1 or 2, characterized in that the cutting tool (40, 42, 48) is an input saw (40). 5. Method according to claim 4, characterized in that the diameter of the inlet saw (42) is greater than the outer diameter of the exhaust gas connection pipe (22). 6. Method according to one of claims 1 to 3, characterized in that the cutting tool (40, 42, 48) is a plasma melting cutting tool (42). 7. Method according to claim 6, characterized in that during the cutting step, a ground (44) of the plasma fusion cutting tool (42) is connected to the gas connection pipe of exhaust (32). 8. Method according to one of claims 1 or 3, characterized in that the cutting tool (40, 42, 48) is a grinding wheel (48). 9. A method according to claim 8, characterized in that a straight grinder (40) is used to operate the grinding wheel (48). 10. Method according to one of claims 1 to 9, comprising a plus a step of enlarging the opening (34) in the inner pipe (30). 11.Procédé according to claim 10, characterized in that a grinder (70) is used to enlarge the opening (34). 12. Method according to one of claims 1 to 11, characterized in that the opening (34) in the inner pipe (30) has a larger diameter than the exhaust gas connection pipe (32). 13. Method according to one of claims 1 to 12, characterized in that the flue gas connection pipe (22) is not damaged. 14. Method according to one of claims 1 to 12, comprising a plus a step of shortening the flue gas connection pipe (22). 301 1 3 1 6 18 15. Method according to one of claims 1 to 14, comprising a plus a step of mounting a wall shutter (80) to the chimney (10). 5 16. Method according to one of claims 1 to 15, characterized in that the step of cutting the exhaust gas connection pipe (32) of the inner pipe (30) is performed in two sections. 17. Method according to one of claims 1 to 16, characterized in that the inner pipe (30) is made of stainless steel, aluminum or a mineral material. 18. Method according to one of claims 1 to 17, characterized in that the outer pipe (20) is a metal pipe stapled sheet metal. 19. Method according to one of claims 1 to 18, characterized in that the exhaust duct (1) extends over several floors of a building and comprises a plurality of combustion air connection pipes (22) 20 and a plurality of exhaust pipes (32), the steps a. to d. being done several times. 20. Method according to one of claims 1 to 19, characterized in that the plastic exhaust pipe (50, 52) comprises a flexible plastic exhaust pipe (52). ). 21. Method according to one of claims 19 or 20, characterized in that the exhaust duct (1) comprises a plurality of flexible or rigid plastic exhaust pipes (50, 52) which are all arranged inside the inner pipe (30).