Coaxial chimney for a gas boiler - design features. How to install a coaxial pipe for a gas boiler - important installation rules Minimum output of a coaxial pipe from the wall

When installing any heating boiler unit (except for an electric one), it is necessary to take care of the smoke removal system and the flow of oxygen, which is necessary to maintain the fuel combustion process. Boilers with combustion chamber closed type Can be installed in any room. Wherein classic scheme there is absolutely no point in extracting combustion products. A coaxial chimney is quite sufficient. In this article we will look at all the rules for installing a coaxial chimney for a gas boiler.

Design

The meaning of the word “coaxial” itself means “coaxial”. These are two tubes inserted into one another and brought out. The pipes do not contact each other from the inside due to the jumper system.

The reason for this is the different purposes of the tubes:

Small - designed to remove products formed during fuel combustion.
The large one is needed to supply air, and therefore oxygen, to the combustion chamber.

In this case, it turns out that fresh air and combustion products do not mix with each other. Such a system is reliably insulated, and the air from the room does not mix with the gases in the chimney.

Important! The most common coaxial structures are horizontal, although, in principle, a vertical chimney can also be installed.

Advantages

The main advantage of this design is its versatility. It can be used for all types of heating boilers. The most efficient work is the installation of coaxial chimneys for gas boilers with a closed combustion chamber and forced draft. The boiler itself can be wall-mounted or floor-mounted.

Here are some more advantages:

The location is horizontal. There is no need to punch a hole in the roof. It is enough to lead the pipe out the window or make a hole in the wall closest to the boiler.
The flue system is isolated and not connected to the air in the room. There is no risk of carbon monoxide entering the room.
The air that comes from the street approaches the combustion chamber already heated, due to the fact that it is in contact with the hot smoke exhaust pipe. This helps to increase the efficiency of the boiler unit.
Easy installation of a coaxial chimney. Work on its arrangement does not require special skill or special knowledge.
Safety. The coaxial flue is reliably protected from the risk of fire, since the system is cooled by relatively cold air from the street.
There is no need to equip a separate boiler room. Any place convenient for you - kitchen, hallway, outbuilding or basement, suitable for boiler installation.

Rules for installing a coaxial chimney for a gas boiler

If you plan to install a coaxial smoke exhaust system, you must adhere to installation and safety rules. This will avoid even the smallest risks associated with exhaust gases entering the premises:

The maximum length of the vertical outlet pipe in a coaxial chimney is 3 m. Sometimes you can find longer chimneys (up to 5 m). For example, this applies to the installation of a coaxial pipe of a Ferroli floor-type double-circuit gas boiler.
The pipe is routed horizontally to the street. Wherein maximum length horizontal section is 1 m.
When installing forced fan draft there is no need to arrange a vertical section.
The height of the flue outlet above the ground is 2 m, and relative to the boiler unit the excess is 1.5 m.
The minimum distance of the chimney pipe outlet from any window or door opening, as well as ventilation grilles, is 0.5 m.
It is not advisable to install a coaxial flue pipe outlet under the window. But if this is unavoidable, the minimum distance between the chimney outlet and the window is 1.0 m.
A slight slope of the pipe ensures condensate removal.

Chimney slope

There is no consensus on this issue:

The most common recommendation is to slope the pipes away from the boiler. In general, this is quite logical. The condensate formed during boiler operation flows out and does not enter the boiler. However, such a system works flawlessly until the onset of severe frosts. In winter cold, the condensate flowing down simply freezes, sometimes even inside the pipe. All this worsens the air intake for the fuel chamber.
You still have to make a decision to slope the pipe towards the boiler. To solve the problem of condensate getting into the boiler unit, an additional condensate collection tank is installed.

Should I insulate the chimney?

The fact is that insulating the flue pipes does not solve the problem. The condensate still freezes. This problem can be solved more effectively by shortening the inner tube slightly. Naturally, this is relevant if the pipes are inclined from the boiler.

Installation procedure

Unlike the usual vertical chimney, the coaxial system does not require any professional skills during installation. But you must strictly follow the instructions. This is the only way to achieve complete safety.

Installation of a coaxial chimney for a gas boiler is carried out according to the following algorithm:

Determined by the location of the boiler unit. Wall-mounted models are placed on external walls, floor-mounted ones - on a slight elevation.

Important! The excess of the outlet on the wall above the boiler, in accordance with the rules, is 1.5 m or more. The diameter of the hole in the wall should be slightly larger than the diameter external pipe.

A special element is installed to connect the chimney to the boiler. All joints and turns are secured with clamps. In this case, under no circumstances should sealants or adhesive tapes be used.

Important! The number of rotary bends for the entire system should not exceed 2.

Comfortable living in your home depends on the efficiency of your heating system. Heating a home involves the use of open fire devices, which reduces the oxygen content in the atmosphere inside the house. Vicious circle? Not at all. The problem is solved by using coaxial chimneys for removing combustion products. What is it and how to build it yourself?

What is a coaxial chimney

An autonomous home heating system for any device requires complete removal of combustion products. Traditional systems chimneys are still used today. However, they are being replaced by new devices that solve several problems simultaneously - coaxial chimneys.

Their appearance is associated with solving the problem of fuel combustion in a furnace, which occurs with the participation of oxygen from the heated room. If concentration is not restored by ventilation, the room becomes stuffy and uncomfortable. The conclusion is obvious - isolate the fuel combustion device (boiler) and supply oxygen to the furnace from the outside. For this purpose, two-layer pipes were used, in which combustion products are removed from the inside, and air from the street is discharged through the gap between the inside and outside.

Coaxial chimney device

Advantages of coaxial chimneys

They are as follows:

Increased efficiency of boiler equipment compared to traditional devices, obtained by supplying heated air with a normal oxygen content to the boiler furnace. This promotes more complete combustion of fuel;
no need for additional supply ventilation in room;
increased environmental friendliness obtained by efficient combustion of fuel;

Flaws

These include the tendency of the inner pipe to freeze. This becomes possible due to the low temperature of the flue gases already at the outlet of the furnace. As a result, condensation forms, which freezes when the outside air temperature is below -15 degrees, which is not at all unusual for Russia. The degree of freezing can completely block the channels of gas and air movement, which means an emergency situation.

Attention! The pipe must not be allowed to completely freeze, as this will damage the boiler equipment.

As practice shows, such phenomena often arise from the desire to maximize the efficiency of the system by reducing the diameter of the internal chimney pipe, which leads to a decrease in the temperature of gases down to the “dew point”, increased condensation and, accordingly, to the formation of ice.

Kinds

Devices for removing combustion products of this type are divided according to several criteria.

Indoor and outdoor systems

Internal systems are located in shafts specially constructed during the construction of the house. In no case do they come into contact with the living space. In some cases, such devices are installed as standard brick chimney, but it should be noted that such chimneys are inconvenient for maintenance and repair.

Methods for installing a chimney in the house

External chimney systems are installed directly on the wall of the house from the outside. There is an opinion that they spoil the design of the house, so they are placed with access to the patio. This device design is easy to install and convenient to maintain and repair.

Exiting a coaxial chimney through the wall of a building

Cold and insulated devices

As noted above, in our harsh winters the chimney freezes. To avoid this effect, you need to insulate the chimney. There are several ways to do this:

Using an additional casing made of a larger diameter pipe. At the same time, the interval between outer pipe and the casing is filled with insulation. Mineral wool is used for this;
Outer pipe of coaxial system wraps roll insulation. On top of this layer, wrap a protective jacket made of aluminum foil and secure it with clamps. The direction of winding should be carried out in such a way as to prevent moisture from leaking into the insulating layer, that is, from the bottom up.

Vertical or horizontal output

Coaxial designs were originally designed as purely horizontal devices. But this is a theory, but in practice the decisive factor is the location of the heating unit, which in some cases requires a combined design.

Vertical outlets are used only for boilers without forced draft.

Internal vertical and external combined coaxial chimney

Design and principle of operation

The coaxial piping kit includes different quantity parts depending on the chimney design.

Design of a coaxial chimney

The main ones are:

adapter for connection to the combustion unit;
90 degree elbow to change the direction of the pipeline;
Straight coaxial pipe. Structurally, it consists of two parts located one inside the other with longitudinal partitions between them;
coupling with seal and clamp to strengthen the joint;
air intake.

The operating principle of a chimney of this design is that when fuel burns, flue gases are formed and immediately rush into the chimney. The created low pressure zone is filled with outside air through the channel between the walls of the pipes. Warming up along the way from the inner pipe, it enters the firebox and the heated oxygen actively reacts with the fuel. At the same time, the efficiency of the device increases significantly. The cooled outer wall is favorable for fire safety devices.

Materials and tools for chimney installation

The completeness of the chimney depends on the location of the heating unit. The device consists of a number of standard units that allow the construction of chimneys of any configuration. The modules are modified, which makes it easy to equip the device with the necessary parts and simplifies installation work. When creating a coaxial chimney, the following components are used:

straight pipes - the main element of the chimney;
tees - made at angles of 30, 90 and 45 degrees, designed to change direction during installation;
couplings and corner bends - pipe connections;
condensate collectors - used in each vertical section, equipped with a water seal to prevent the suction of outside air, which reduces the draft in the chimney;
inserts with inspection windows for chimney repair and maintenance;
Inlet and outlet nozzles - included with the heads, are used to remove furnace gases and take air from the atmosphere. The outlet nozzle is installed at a distance from the air intake to avoid mixing clean air with combustion products;
adapter - devices for connecting the chimney to the heat generator;
fastening fittings in the form of flanges, clamps and brackets;

The material for the manufacture of chimney elements can be:

Stainless steel sheet.
Galvanized sheet.
Heat-resistant plastic.
Aluminum alloys.

The general requirement for them is resistance to temperatures of at least 250–300 degrees.

When assembling the chimney it is used simplest tool for installing fasteners such as screwdrivers and wrenches. To attach the brackets to the walls you will need an electric drill and plastic inserts - dowels. Hole in brick wall can be done with a bolt and a chisel.

Preparing for chimney installation

Despite the apparent simplicity of the chimney assembly process, it must occur according to a certain algorithm:

Purchase of a heat generator. It should be taken into account that coaxial chimneys are used only with closed type devices with forced draft. Their power is up to 30 kW.
Determining the installation location, securing.
Execution of a preliminary design of a chimney taking into account bends, rise and other features depending on the architecture of the building.
Purchase of a set of standard parts that ensure exact fulfillment of the requirements of the preliminary design.

DIY installation of a coaxial chimney

Before you begin assembling the chimney, you need to clearly understand the basic regulatory provisions:

Rules for the removal of combustion products

When assembling the chimney, you must adhere to the following rules:

The straight section crossing the wall should be installed with a slope of 3 degrees towards the street for unimpeded drainage of condensate.
The chimney channel along its entire length should not include more than two elbows.
Inspection windows, transition devices and condensate collectors must be installed in easily accessible places for ease of use.
The chimney should not be discharged below ground level. The distance to the nearest building must be at least 8 meters. When using a deflector at the end of the chimney, this distance can be reduced to two meters for a blank wall and to five for a building with window openings.
A horizontal chimney installed in a location with prevailing winds opposite in the direction of smoke removal must be equipped with a visor - a damper. It should be located no further than 40 cm from the smoke outlet.
Coaxial chimneys located at a height of less than 1.8 meters must be equipped with a reflector grille to protect against hot smoke.

Installation of a horizontal coaxial chimney

Compliance with these rules will allow for safe operation of the heating device with high-quality removal of combustion products.

Assembly order

Installation of a horizontal coaxial chimney is carried out as follows:

connecting the adapter from the heat generator to the chimney;
installation on the elbow adapter to change the direction of the channel;
Marking the location for making a hole in the wall corresponding to the diameter of the chimney pipe. Important! the junction of the pipeline elements should not be located inside the wall;
installation of decorative caps at the intersection of the chimney and the wall;
installing a deflector at the end;
installation of an inspection unit and a condensate collector.

Upon completion of assembly, it is necessary to check that the assembled device complies with all the rules outlined above. Something to remember! The use of sealing gels and sealants in coaxial chimneys is prohibited.

Installing a coaxial chimney vertically, as a rule, is a necessary measure due to the impossibility of performing it horizontally without violating the installation rules. The peculiarity of the design is that such combustion product outlets cannot be installed in a straight line from the furnace due to the formation of a large amount of condensate. With this design, it will fall directly into the firebox, which is extremely undesirable. Therefore, you need to make an elbow from the stove for the horizontal component. Next, a second elbow and a condensate collector are installed. After this, the chimney is mounted vertically. The intersection with the ceiling and roofing pie is carried out using insulating glasses. On the roof, the pipe is equipped with a sealing umbrella to prevent leaks.

Attention! A vertical coaxial chimney is not used for closed boilers with forced draft.

Features of operation

First of all, you need to pay attention to the noticeably more high efficiency furnaces with such devices for removing combustion products. The efficiency increases due to the optimal fuel combustion mode.

With normal heating of a home, the air in it does not deteriorate, remaining clean, since oxygen from the outside air is used for combustion. There is no need for mandatory organization of supply ventilation, although it is usually created anyway; it will not be superfluous.

Coaxial chimneys are characterized by long-term operation because the pipes, which are constantly cooled by an influx of air, do not overheat.

Repair and service

The device requires virtually no special maintenance. At first heating season you need to inspect all fasteners and ties, tighten loose connections.

A regular maintenance activity is periodic draining of condensate from the storage tank. Moreover, the frequency of such an operation is determined by the weather, which affects its formation.

The need to clean the inner pipe wall is determined by a visual inspection through the inspection window before the start of the heating season. The procedure is performed with a special brush equipped with stiff bristles. Apply chemicals, softening carbon deposits and soot.

Coaxial chimneys should be considered the most advanced for saving heating costs, decreasing by 15–20%. At the same time, living conditions in the house improve.

Coaxial - This word means the presence of one object within another. The coaxial chimney for wall-mounted gas boilers is built using a “pipe-in-pipe” system. . The chimney is a double-circuit design, in which a pipe with a smaller diameter is located in a pipe with a larger cross-section. Inside, the pipes are connected to each other only using jumpers that prevent them from touching.

Coaxial chimneys are used for heat generators with closed combustion chambers. Such heat generators can be not only gas boilers, but also convectors, radiators and others.

A coaxial chimney for a gas boiler performs 2 functions at once: it removes combustion products outside and provides an influx of fresh air, which is necessary to maintain the gas combustion process in the chamber.

As a rule, for boilers that have a closed combustion chamber, the length of the chimney does not exceed two meters. It is worth noting that often the chimney is laid simply through the wall to the street. It is very rare, but you can find a vertical coaxial chimney, led out to the street through the ceiling and roof.

Advice! When installing a coaxial chimney, you should try to ensure that the pipes have only a horizontal direction.

If the place in the wall where the chimney is supposed to be installed is located next to a window, then it is better to install the chimney just above the roof. In this case, you will definitely have to assemble the vertical section of the chimney.

The standard set of coaxial chimney for wall-mounted boilers contains the following components:

straight pipes;
tee;
cleaning;
condensate collector;
upper chimney tip;
knee (rotation angle is 90°).

Straight pipes are the direct former of the chimney. The elbow is intended for connection between the horizontal part of the chimney and the vertical, as well as for connecting the horizontal chimney with a gas boiler.

If the chimney has only a horizontal orientation, then the kit includes the following elements:

set of straight pipes;
knee (rotation angle 90°);
side chimney tip.

At the moment, the industry offers coaxial chimneys for gas boilers in the following range:

chimneys made of stainless acid-resistant steel;
chimneys for gas boilers made of stainless steel;
coaxial chimneys for gas boilers made of galvanized steel.

In addition, it is worth considering that there are chimneys that have different combinations, that is, the outer and inner pipes can be made of different steel.

Advantages of coaxial chimneys

The first and main advantage of coaxial chimneys is that the air to support the combustion process is taken not from the room, but from the outside. A conventional furnace takes oxygen from the room where it is installed, so it often has to be ventilated to get rid of the lack of fresh air.

The principle of operation of a coaxial chimney is slightly different (see). The combustion product enters the inner pipe, but fresh air flows through the outer pipe.

This design solves several problems that are typical for conventional heating appliances and chimneys:

The air that comes from the outside comes already hot, since it is heated by the inner pipe due to the passage of highly heated combustion products through it. This greatly reduces heat losses, and as a consequence, increases the efficiency of the entire heating system.
Higher efficiency leads to natural gas is burned completely. This ensures that particles of unburned fuel are not emitted into the atmosphere, this increases the environmental friendliness of the boiler.
Of no small importance is the fact that the inner pipe, transferring part of its heat to the outer one, becomes less hot. This reduces the risk of fire at the point of contact between the pipe and flammable parts of the room (wallpaper, wood paneling and others).
All heating processes, from the moment clean air enters and until the combustion products are removed, take place in a closed space - the combustion chamber. This makes it more comfortable for a person, since there is no need to take care of additional ventilation of the room into which smoke and carbon monoxide could enter, that is, maximum safety is ensured;
The presence of a large assortment of pipe sizes - both external and internal - contributes to the fact that It is possible to choose a coaxial chimney for a gas boiler of any power.
Small size, which greatly saves space indoors.

The advantages include the simplest installation. If during the installation of a conventional chimney pipe many difficulties arise, then the installation of a coaxial chimney can be done independently. We can also talk about the relative ease of operation and maintenance of such a heating system.

Installation of coaxial chimneys

All the advantages that a coaxial chimney for a gas boiler has, including safety and environmental friendliness, can be reduced to zero. This situation occurs when the coaxial chimney was installed incorrectly.

Advice! Before you begin installing a coaxial chimney, you should make sure that you have all the necessary elements of the chimney itself, as well as tools and other materials.

In order to install a chimney, you need:

coaxial pipe or several pipes;
smoke exhaust pipe;
connection adapter;
wall linings - 2 pieces;
flange for linings;
connecting clamp;
tip on the pipe.

The chimney is attached to the pipe heating installation and goes outside the room. If there are any obstructing objects, it is better to remove them before removing the chimney. In addition, if possible, you need to remove flammable substances and objects from the pipe at a safe distance.

In any case, installation begins with choosing a location. This is easier to do when you have already decided on the choice of installation location for the boiler itself. It is better to install gas boilers with a coaxial chimney together. The best option will be if the distance from the chimney to the boiler is approximately 1–1.5 m. If there is a need, the length of the chimney can be increased, but so that there are no more than 2 bends in total, and the maximum length is 3m.

Hole smoke channel should be placed in compliance with certain rules:

distance from the ground – at least 2 meters;
the minimum distance from the door and windows is at least 50 cm

Next, as already noted, you need to remove everything unnecessary from the selected location to a safe distance. After this, you can begin installation by starting to drill the hole required diameter, which can vary from 11 before 12.5 cm.

Next, the pipe is connected to the outlet neck of the heating installation using a clamp, which is clamped with bolts on both sides. After this, the chimney of the required configuration is installed. All connections are made using clamps. The chimney exiting the room should have a slight slope so that moisture (condensation) can easily be removed on its own.

After the chimney is installed, installation is carried out decorative overlays, which perform only an aesthetic function.

Insulation of coaxial chimneys

Sometimes a problem arises that coaxial chimneys for gas boilers freeze.

A simple solution seems to be simply insulating it (see). However, this doesn't help. It is for this reason that insulation of coaxial chimneys is not practiced. The only way out of this situation is to reduce the size of the chimney itself.

If the tip freezes due to condensate entering the air intake pipe from a pipe with combustion products, then the length of the inner pipe must be reduced relative to the outer one.

The most the best option there will be an option to install 2 separate pipes, the insulation of which has a much greater effect than the insulation of a coaxial chimney.

Everyone knows that performance heating systems, which use the principle of fuel combustion, is impossible without oxygen to support 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 by the owner in the work process.

Design and purpose of a coaxial chimney

This device looks more like a motorcycle exhaust pipe. In fact, this is a specially designed structure, a pipe in a pipe with different diameters, which are inserted one inside the other and rigidly fixed to each other. Combustion products are removed through the inner tube, and the air necessary for combustion of the fuel enters the combustion chamber through the space between the inner and outer tubes. A coaxial chimney for a gas boiler solves two main problems at once: removing exhaust gases and supplying air to the device.

Such chimneys are made of round pipes, with the inner one most often made of aluminum alloy, and the outer one made of steel, thickness 1; 1.5 or 2 mm. The ratio of internal and external diameters for wall and floor heating devices is 60 to 100 mm. For condensing boilers, chimneys with a diameter ratio of 80 to 125 mm are used.

There are two types of coaxial chimneys: horizontal and vertical. The easiest to install, and therefore the most common smoke exhaust system of this type, is a horizontal chimney. A vertical coaxial chimney is quite difficult to install and is therefore used if horizontal installation is not possible or heating device before street wall more than 4 m.

Advantages and disadvantages

As mentioned above, this type of smoke exhaust system is used only for gas equipment with a closed combustion chamber, namely:

Dual-circuit heating boilers wall and floor installation with a closed combustion chamber.
Gas hot water heaters.
Generators and convectors.

The main advantages of such an air intake and smoke removal system are:

Safety. In such a chimney exhaust system, heat exchange occurs between street air and exhaust gases, resulting in a decrease in the temperature of combustion products.
Heating air coming from the street by contacting it through the pipe wall significantly increases the efficiency of the boiler.
The coaxial chimney draws in outside air and not from the room, which prevents the creation of a vacuum that interferes with the normal operation of the boiler and natural circulation indoor air.
Easy installation and a large number of accessories.
Significant savings in internal space.
Oxygen from the room is not used.

The most attractive for using chimneys of this type are apartment buildings, since the outlier carbon monoxide and fuel combustion products are produced not into the ventilation shaft, but directly into the atmosphere.

Such chimneys also have disadvantages, namely: quite expensive insulation to prevent freezing of the chimney head. The possibility of freezing of the pipe head is quite high. This happens because the temperature of the exhaust gases is too low and is not able to melt the ice formed when moist air escapes. The consequences of icing can be quite serious: repair of burners, combustion chambers and turbocharging.

Installation diagrams and installation requirements

As mentioned above, there are two main schemes for installing a coaxial chimney: vertical and horizontal. During installation, you 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 the set of “Safety Rules in the Gas Industry”.

The total length of the coaxial chimney cannot be more than 4 m. If a larger length of the smoke exhaust system is required, then a larger coaxial chimney should be used.

When installed vertically, 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 own equipment. To achieve the required length of the chimney, special extensions are used.

To ensure tightness when the chimney passes through the roof and protect it from atmospheric precipitation a device called a terminal is used.

When installing a vertical smoke exhaust system, you should be guided by the rules that regulate its height, depending on its location in relation to the ridge of the pitched roof.

Most often, a vertical coaxial chimney is installed in private houses. But there is another option for a vertical smoke exhaust system - collective, which is designed for apartment buildings. General coaxial chimney in apartment building makes the use of individual gas heating appliances completely safe.

Horizontal exhaust gas outlet is most often used for wall mounting heating equipment. The horizontal scheme involves the exhaust of the chimney through the outer wall to the street.

During installation, you should take into account the slope of the chimney of 2-3° to prevent condensate from entering the boiler unit.

To pass through the wall, two types of devices are used: 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.

Self-installation

Installing a coaxial chimney with your own hands is quite simple and anyone can do this work House master with basic skills in using power tools.

To complete the work, you will need a kit that includes: a pipe with a flange, a clamp, an adapter for connecting to the boiler unit and a coaxial elbow. If necessary, you should purchase a special coaxial chimney extension.

IN in the right place make a hole in external wall. 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.
Connect the chimney directly to it using a crimp clamp. If you need to bring the structure to the wall, then use a knee. Secure everything with crimp clamps.
Exit the pipe through the hole, providing a slope towards the exit of 2-3 °.
Seal the cracks polyurethane foam or mineral wool.
Cover the pipe exit with a decorative cover.

It should be noted that with each rotation of the chimney by 90°, the maximum length of the coaxial chimney decreases by 0.5 m.

Content

Design and principle of operation
Advantages of coaxial chimneys
Installation and connection to a gas boiler

Introduction

The main feature of gas boilers with a closed combustion chamber is that they use outside air for combustion. They also need a chimney to release combustion products into the atmosphere. Both of these functions are combined in a unique device - a coaxial chimney for a gas boiler.

In this article we will talk about the design, operating principle and advantages of coaxial chimneys, the requirements and regulations governing their installation in private houses and apartments, as well as what you should pay attention to when doing the installation yourself.

Design and principle of operation

Wall-mounted and floor-standing gas boilers are divided into two large groups: with an open and closed combustion chamber. The first ones use air from the room to work. That is why there must be good ventilation in the place where such a boiler is installed. To remove gases, traditional chimneys made of material suitable for working with aggressive environments are used.

Boilers with a closed combustion chamber are completely isolated from the room. Air is supplied to them from the outside, and flue gases are also discharged there. A coaxial chimney is designed to perform both of these functions simultaneously. What is its structure?

Photo 1: Coaxial chimney installation

The term coaxial in technical marking means two-wire. An analogue of the veins in a chimney is made of two pipes of different diameters, inserted into one another. To hold the inner pipe in the center of the outer pipe, they are connected to each other by special spacers. In addition to performing their main function, they also give the structure additional rigidity.

The operating principle of a coaxial chimney is very simple. Along the inner pipe environment Gas combustion products are removed, and at the same time, the air necessary for combustion enters the gas boiler through the external pipe.

Most often together with gas boilers horizontal coaxial chimneys of short length are used. They come out right through the wall country house or ordinary apartment. There is also a vertical structure, which is mounted in the usual way through holes in the ceilings and roof.

Photo 2: Coaxial chimney kit with anti-icing

To combat glaciation horizontal installation, a special design is often used. Its peculiarity is that the pipe for removing combustion products protrudes from the air intake pipe to a considerable distance. Openings for air intake are located only in the lower part of the outer pipe, which prevents precipitation from entering inside.

The most common are 60/100 coaxial chimneys with an internal pipe with a diameter of 60 mm and an external pipe with a diameter of 100 mm. Models with such parameters are produced by many manufacturers, such as: Baxi, Vaillant, Buderus, Bosch, Viessmann, Ariston, Ferroli, Electrolux.

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Advantages of coaxial chimneys

Despite its simplicity, the advantages of a coaxial chimney are quite significant. In addition to the obvious advantages of this design, there are a number of advantages that do not immediately come to mind. Let's look at them all in order:

Photo 3: Vaillant 60/100 coaxial chimney system

The combustion chamber is completely isolated, so the boiler does not burn out the air in the room. The entry of carbon monoxide into the living space is also excluded. For this reason, installing a heating device does not require the organization of a special boiler room, such as for example. It can be installed even in a room in an ordinary apartment in a typical multi-storey building.
Passing from the outside to the inside, the air is heated by flue gases flowing through the adjacent channel in the opposite direction. Thanks to this, the efficiency of the gas boiler increases.
The outer walls of the chimney have a safe temperature, thanks to the cooling of the central channel by the flow of outside air directed into the system. This increases the fire safety of the system in contact with elements of the building’s cladding and floors.
Installation of a coaxial chimney is very simple. For installation, you do not need to involve expensive specialists and carry out serious redevelopment with large-scale construction work. All work can be done by the owner with his own hands.

Despite the apparent simplicity of connecting a gas boiler to a coaxial chimney, during installation some requirements must be met, which are in many ways similar to the rules for installing chimneys with. The safety and efficiency of the entire system depends on their implementation.

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Installation and connection to a gas boiler

As we have already found out, a coaxial chimney can be installed both vertically and horizontally. It is much easier to build a horizontal chimney, however, due to poor natural draft, it is only suitable for those models that are equipped with exhaust fans.

Installation work gas chimneys regulated regulatory documents SNiP SP 42-101-2003. We will list the basic rules and points that should be taken into account when installing coaxial chimneys. Let's start with horizontal structures:

When purchasing a coaxial chimney kit, you should make a choice based on its cross-section. It should not be smaller than the outlet pipe of the gas boiler.
According to the regulated rules for installing chimneys, the length of the horizontal section should be no more than 3 m. Some manufacturers recommend longer lengths for their models, relying on the increased power of exhaust fans.
The installation of a coaxial chimney should be carried out at an inclination of 3° per meter of pipe away from the boiler. This is done in order to set the direction for the drainage of the resulting condensate.
When planning a place for a hole in the wall, it should be taken into account that there should be a distance of 0.5-1 m from the boiler outlet to the wall. This is done in order to avoid icing of the chimney inside the room when low temperatures in winter.
When installing a gas boiler near windows, it should be taken into account that the distance from the outer pipe of the coaxial chimney to the nearest window must be at least 0.5 m. It is strongly not recommended to place the pipe under the window. If there is no other possibility, then it should be at least 1 m below the window level. The distance to the gas supply pipe should be at least half the diameter of the coaxial chimney.
To avoid contamination, the external pipe must exit at a distance of at least 2 meters from the ground surface.
If the coaxial chimney is located under a canopy or balcony, then it must have a certain length of the protruding part. How to determine it is shown in the following figure:

Photo 4: Rules for installing a coaxial chimney under a canopy

A vertical coaxial chimney is installed if for some reason it is impossible to install a horizontal one. Installation of this design is more complex and is subject to the same requirements as for installation chimney for a solid fuel heater such as . We list the main points that are worth paying attention to:

When assembling chimney elbows for a gas boiler, each upper elbow should be inserted inside the previous one and connected with clamps. If this rule is violated, condensate will penetrate through the joints and flow down the outer walls of the chimney.
To collect condensate, ease of cleaning and maintenance, a tee is required to be installed at the bottom of the structure.
Special attention should be given to the section of the coaxial chimney located on the roof. How this part of the chimney should be built is clearly shown in the following figure:

Photo 5: Requirements for installing a coaxial chimney on the roof

Attention: Due to the risk of icing, the installation of protective caps (deflectors) on gas chimney pipes is prohibited.

To see more clearly how to properly install a coaxial chimney, see the following video: