A double-walled coaxial chimney is used to divert combustion products from gas boilers and columns equipped with a closed combustion chamber. It greatly simplifies the installation of water heaters in terms of smoke removal, you do not have to build a classic pipe from a modular sandwich or ceramic blocks. The procedure is as follows: we get acquainted with the design, study the requirements for the installation of a coaxial chimney and do the installation work with our own hands, using this guide.
Chimney device for turbo boiler
The coaxial gas duct is a double-walled pipe-in-pipe construction, which simultaneously performs 2 functions: smoke extraction to the outside and air intake for combustion from the street. Hot gases move along the internal channel, the air flow goes towards the external (between the two walls).
An important point. The forced movement of combustion products and air is provided by the gas boiler fan, natural draft does not work here. At the same time, a coaxial chimney must not be connected to turbocharged units using other types of fuel - wood, pellet or diesel.
The 2 in 1 chimney system “air / combustion products” offers the following benefits:
- Hot gases give off part of the heat to the air stream, the combustion process improves, the efficiency of the heat generator increases.
- The coaxial pipe is brought out horizontally, by the shortest route through an opening in the outer wall. In some cases, vertical mounting is possible.
- Thanks to the double-walled design of the gas duct, a turbo-boiler or a column can be installed in almost any room without a traditional smoke channel - a kitchen of a country cottage, a garage, a basement, and even in a bathhouse. The room must meet the requirements for gas boiler rooms.
- The owner does not need to worry about the additional flow of air needed for combustion. Although general ventilation should still be done.
Clarification. In apartment buildings, it is forbidden to display a horizontal smoke channel into the street through the wall.
The disadvantage of the chimney system is the freezing of the head in severe frost. The intake air contacts the hot wall of the inner pipe and releases condensation forming an icicle. The problem is solved by installing a special stainless steel extension cord.
The main elements of a coaxial chimney:
- a straight section with a tip at the end;
- the same double-walled outlet at 90 ° or 45 °;
- adapter - adapter to the coaxial output of the boiler;
- connecting clamps, flanges;
- elastic cuffs, aprons;
- revision section with steam trap (for vertical installation);
- fasteners.
Note. Different adapters can be used to connect to different heaters. For example, Viessmann Vitopend wall-mounted boilers are already equipped with a flange and a nozzle, and these parts are supplied separately to the Vaillant Turbo heat generator.
How to correctly install coaxial elements, we will describe further. But first, let’s propose to study ...
Installation requirements
In normative documents, the installation of a coaxial chimney is not separately prescribed. 2 rules should be followed: follow the recommendations of the gas boiler manufacturer and the general requirements for the removal of combustion products from gas-using plants:
- the maximum length of the horizontal pipe section is 3 m;
- the passage section of the chimney must correspond to the size of the outlet pipe of the heat generator;
- if 2 gas water heaters are installed in the furnace room (for example, a column + a boiler), two separate coaxial pipes must be made, it is forbidden to reduce them to one;
- when crossing walls and ceilings of non-combustible materials (aerated concrete, brick, reinforced concrete), it is enough to install a metal or asbestos sleeve;
- in a wooden house, it will be necessary to arrange fire cutting in the wall, that is, to ensure a minimum distance of 380 mm from the wall of the chimney to the combustible structure.
A separate nuance is the installation of an umbrella on the tip of the flue, vertically removed through the roof. Norms strictly forbid to cover chimneys of gas heat generators with caps. On the other hand, the unit must be protected from precipitation through the coaxial system.
Tip. Contradictions arising from an imperfect regulatory framework are easily resolved. Contact the gas service in your area and find out the specific installation requirements for air / combustion systems. Before installing the boiler, you still have to get permission from them, order a project, and then put the facility into operation.
In the installation instructions, manufacturers of heating units require compliance with the following rules:
- minimum spacing from the ceiling to a horizontally laid chimney - 200 mm;
- the distance from the wall to the end of the pipe is not less than 30 cm;
- head height above ground level - at least 2 m, better than 2.5 m;
- a gap of 600 mm should remain between the chimney slice and the nearest building or fence, optimally 1.5 m;
- when choosing the location of the outlet channel, it is important to provide a spacing of 60 cm from the window or supply air;
- the slope of the chimney of the turbocharged boiler is made towards the street (value - 10 mm per meter pipe length);
- condensing units use the energy of water vapor, so the coaxial chimney is installed with a slope towards the heat generator.
On forums, homeowners often ask if the boiler room needs ventilation with a coaxial chimney. We answer: through the external channel of the system, the fan draws in the amount of air needed for combustion. Ventilation in the furnace (3-time air exchange) is still needed, it removes carbon monoxide, methane or propane in case of leakage.
Wiring diagram and selection of accessories
There are only 2 basic schemes for installing coaxial systems, the rest are their variations:
- horizontally from the boiler out in the shortest way;
- vertically through the ceiling and roof.
In the case of double-walled chimneys, the second scheme is rarely used, since it is rather complicated in execution. Laying through the ceilings is realized in situations where it is impossible to bring the channel into the wall - a high fence is built right next to it, several windows are nearby and other factors interfering with the correct installation.
Most often, scheme No. 1 is used - horizontal installation of a coaxial chimney. Schedule the route of the pipe, measure the length and buy a ready-made set of parts listed in the first section of the publication.
What are the nuances to consider:
- The diameter of the channel is selected strictly according to the coaxial output of the water heater. Most heat generators use 2 sizes - 60/100 and 80/125 mm. The first figure shows the diameter of the duct, the second - the external duct.
- An adapter is used to connect the air-smoke channel to the heating unit - an adapter suitable for a specific boiler model.
- The gap between the pipe and the wall case is sealed with fireproof material - basalt wool, asbestos cord. Do not blow out the cracks with polyurethane foam.
- The chimney can be lengthened (build up with additional direct sections), not exceeding the value specified in the boiler passport. The indicator depends on the performance of the fan.
- If the gas duct is too short, a restriction orifice of a certain diameter must be set. Otherwise, the smoke exhauster pumps more air into the furnace than is necessary.
- In regions with a cold climate, a nozzle should be used to prevent icing of the head.
- The smoke channel in transit through an unheated room is best insulated from the outside with a layer of basalt fiber.
Reference. In the passport of the Viessmann Vitopend supercharged boiler, the diameters of the installed diaphragms are indicated depending on the length of the chimney. For example, a 60/100 mm pipe up to 3 m long is equipped with a 44 mm diaphragm.
When it is necessary to vertically remove the coaxial gas duct from the basement or basement, a revision section with a steam trap fitting is required. If the total length of the route exceeds the permissible limit, instead of a double-walled single pipe, 2 separate ones are laid - a chimney and an air duct of 80/80 mm. A special adapter-divider, shown in the photo, is connected to the boiler output.
How to install a coaxial chimney
Installation of the “air / combustion products” system is extremely simple. The pipe section and elbow are connected “into the socket”, no gaskets or sealants are used (there is already an o-ring on the inner channel). How to mount a horizontal chimney:
- Install the wall or floor boiler in the design position. Make an outer hole, mark the route of the gasket with a pencil on the wall.
- Connect a 90 ° branch or a straight section to the boiler fitting, depending on the wiring diagram. Different adapters are used here - in some models you must first put a metal sleeve, in others - screw a flange to the unit body.
- Attach the next section, before joining, put elastic cuffs on the pipe.
- Tighten the cuffs to the joint, install the clamp on top, then twist it with the screws from the kit.
- Wear a decorative interior apron on the pipe through the wall. Install a section of the coaxial chimney with an outer tip (divider), seal the gaps.
- If the flue was lengthened during installation, attach the pipe to the wall with special clamps.
An important point. The joint of two sections should not be in the thickness of the wall, this is a gross violation of fire regulations. The pipeline passing through the ceiling or wall must be solid.
Conclusion
As you yourself could see, installing a coaxial chimney system for a gas boiler with a closed firebox is a simple operation. If you have found the opportunity to drill a wall yourself and suspend a heat generator, then there are no problems with installing a double chimney flue. Difficulties arise when it is necessary to lead a pipe through the roof - here you have to tinker with the nodes of the passage and seal the coating. The task is facilitated by the separation of channels, the chimney is discharged onto the roof, and the duct into the wall.