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Everyone knows that the performance of heating systems that use the principle of fuel combustion is impossible without oxygen, which supports combustion and proper removal of exhaust gases. Today, to create autonomous heating systems, various gas equipment is in great demand. It is compact and safe, easy to use, perfectly automated and does not require constant intervention of the owner in the work process.
The device and purpose of the coaxial chimney
This device looks more like a motorcycle exhaust pipe. In fact, this is a specially designed design, a pipe in a pipe with different diameters, which are inserted one inside the other and rigidly fixed to each other. Combustion products are discharged through the inner tube, and the air necessary for fuel combustion enters the combustion chamber through the space between the inner and outer tubes. A coaxial chimney for a gas boiler solves two main tasks at once: exhaust gases and air supply to the device.
Such chimneys are made of pipes of circular cross section, and the inner one is most often made of aluminum alloy, and the outer one is made of steel, with a thickness of 1; 1.5 or 2 mm. The ratio of the inner and outer diameter for wall and floor heaters is 60 to 100 mm. For condensing boilers, chimneys are used, with a diameter ratio of 80 to 125 mm.
There are two types of coaxial chimneys: horizontal and vertical. The easiest to install, and accordingly, the most common smoke exhaust system of this type is a horizontal chimney. A vertical coaxial chimney is quite difficult to install and therefore is used if horizontal installation is not possible or if there is more than 4 m from the heater to the street wall.
Advantages and disadvantages
As mentioned above, this type of smoke exhaust system is used only for gas equipment with a closed combustion chamber, namely:
- Double-circuit heating boilers for wall and floor arrangement with a closed combustion chamber.
- Gas water heaters.
- Generators and convectors.
The main advantages of such an air intake and smoke exhaust system are:
- Safety. In such a chimney system, heat exchange occurs between outdoor air and exhaust gases, as a result of which the temperature of the combustion products decreases.
- Heating the air coming from the street by contacting it through the pipe wall significantly increases the efficiency of the boiler.
- The coaxial chimney draws outside air, and not from the room, so that no vacuum is created, which prevents the normal operation of the boiler and the natural circulation of air in the room.
- Easy installation and a large number of accessories.
- Significant savings in interior space.
- Oxygen from the room is not used.
The most attractive for the use of chimneys of this type are apartment buildings, since the emission of carbon monoxide and fuel combustion products is not carried out into the ventilation shaft, but directly into the atmosphere.
Such chimneys also have disadvantages, namely: rather expensive insulation to prevent freezing of the chimney cap. The possibility of freezing of the pipe head is quite high. This happens because the temperature of the outgoing gases is too low and is not able to melt the ice formed during the exit of moist air. The consequences of icing can be quite serious: repairs to burners, combustion chambers and turbocharging.
Mounting diagrams and installation requirements
As mentioned above, there are two main installation schemes for a coaxial chimney: vertical and horizontal. During installation, one should adhere to certain rules for installing a coaxial chimney, regulated by SNiP 2.04.08–87; SNiP 2.04.05–91.3, as well as a set of «Safety Rules in the gas industry».
The total length of the coaxial chimney cannot exceed 4 m.
With vertical installation, the chimney passes through the ceiling and roof. In order to install the system in a vertical position, a special adapter is used.
It should be noted that such an adapter is not a universal device and each manufacturer produces this device strictly for its equipment. To achieve the required length of the chimney, special extensions are used.
To ensure tightness during the passage of the chimney through the roof and protect it from precipitation, a device called a terminal is used.
When installing a vertical smoke exhaust system, one should be guided by the rules that regulate its height, depending on the location in relation to the ridge of the pitched roof.
Most often, a vertical coaxial chimney is mounted in private homes. But there is another option for a vertical smoke exhaust system — a collective one, which is designed for apartment buildings. A common coaxial chimney in an apartment building makes the use of individual gas heaters completely safe.
The horizontal outlet of exhaust gases is most often used for wall-mounted heating equipment. The horizontal scheme implies the output of the chimney through the outer wall to the street.
During installation, the slope of the chimney of 2-3° should be taken into account to prevent condensate from entering the boiler.
Two types of fixtures are used to pass through the wall: basic or horizontal. The only difference between these kits is the adapter for connecting to the heating device. If, when passing through a wall, it is necessary to go around a beam, reinforcement, etc., then special bends and elbows are used.
Installing a coaxial chimney with your own hands is quite simple and any home craftsman with basic skills in using power tools can do this work.
To perform the work, you will need a kit that includes: a pipe with a flange, a clamp, an adapter for connecting to a boiler unit and a coaxial elbow. If necessary, you should purchase a special extension of the coaxial chimney.
- Make a hole in the outer wall at the desired location. It should be noted that the chimney outlet should not be located closer than 0.6 m to the window.
- Connect the adapter to the boiler.
- To it, using a crimp collar, connect directly the chimney. If you want to bring the structure to the wall, then use the knee. Secure everything with zip ties.
- Lead the pipe through the hole, providing a slope towards the outlet of 2-3 °.
- Seal the gaps with mounting foam or mineral wool.
- Close the pipe outlet with a decorative overlay.
It should be noted that with each turn of the chimney by 90 °, the maximum length of the coaxial chimney decreases by 0.5 m.