Coaxial chimney device and standards for its installation

Unique Device

The very concept of coaxial is a symbiosis of two devices, which are pipes inserted one into the other. That is, they have different diameters. In order for the inner pipe to hold well in the outer one, jumpers are installed between them, which prevent the pipes from touching each other. The design is simple, but it is in it that the principle of operation of this device lies.

This is an unusual chimney device for gas boiler Designed for a heating unit with a closed combustion chamber. Why for him?

• Firstly, this device allows not only to remove carbon monoxide gases, but also to supply fresh air to the combustion chamber.The principle of operation is as follows: exhaust gases are discharged through the inner pipe, and fresh air from the street enters the furnace directly through the annular space into the gas boiler directly into the furnace.
• Secondly, since the air enters through the chimney, there is no need in the room where the gas boiler is installed to use a ventilation system that supplies air for gas combustion. That is, there is no need to take oxygen from the room. This is why closed chamber boilers work great with this type of chimney.

Installation method

What problems does the installation of a coaxial chimney solve?

The first two have already been mentioned above, but there are several more problems, or rather, the functions that a coaxial chimney performs better than a conventional outlet pipe design.

• Reduced heat loss. It turns out that the air entering the furnace, when passing through the annulus of the chimney, is very hot due to contact with the pipe, which removes carbon monoxide. And this suggests that natural gas in the furnace will burn more efficiently, hence the increased efficiency.
• The risk of ignition of carbon monoxide flue gases is reduced. The thing is that when cold air from the outside comes into contact with the products of gas combustion inside the chimney, the latter are greatly cooled. That is, the requirements for a chimney for a gas boiler, which are imposed by fire safety rules, are strictly observed.
• Returning to the high efficiency, we note that almost complete combustion of fuel occurs in the furnace, which means that unburned particles will not pollute the environment. That is, the indicator of environmental friendliness of this boiler is the highest.
• We return to the arrangement of the premises with a ventilation system.The chamber at the boiler is closed, the coaxial chimney completely provides the unit with both fresh air and efficient removal of carbon monoxide. So the safety of people in this room is one hundred percent.
• The small dimensions of the pipe make it possible to save space.
• Manufacturers today offer a fairly wide range of coaxial chimneys that will fit any gas boiler with any power. A distinctive feature of pipes in this indicator is their diameter.

Differences between the two types of chimney

By the way, correct selection of diameter a coaxial chimney for a gas boiler is the main requirement for the efficient operation of the heater itself. More recently, consumers have faced one rather serious problem. Condensation has collected inside the chimney. Why did this happen? Because the manufacturers of the first models did not expect them to withstand low temperatures of minus 20-30°C.

It so happened that the contact of very cold air and hot flue gases caused the formation of condensate, which not only quickly disabled the chimney, but also greatly reduced the efficiency of the gas boiler. The reason turned out to be an incorrectly carried out heat engineering calculation of the chimney for a gas boiler. After all, manufacturers sought to increase efficiency to the maximum, and this could happen only in one case - a decrease in the diameter of the pipe. It was then that a surprise awaited everyone - the chimney just began to freeze over. And the efficiency, thus, has not increased. It was the wrong way.

The installation of a chimney can be considered using the example of a double-circuit design

Chimneys for a gas boiler are being installed in the direction of the structure from the bottom up, that is, from the heating objects of the room towards the chimney. With this installation, the inner tube is put on the previous one, and the outer tube is inserted on the previous one.

All pipes are fastened to each other with clamps, and along the entire laying line, every 1.5–2 meters, brackets are installed to secure the pipe on a wall or other building element. A clamp is a special fastening element, with the help of which not only the parts are connected to each other, but also the tightness of the joints is ensured.

The laid sections of the structure in the horizontal direction up to 1 meter should not come into contact with elements that pass close to the communications. The working channels of the chimney are placed along the walls of buildings.

Be sure to install a bracket on the wall every 2 meters of the chimney, and the tee is attached using a support bracket. If it is necessary to fix the channel on a wooden wall, then the pipe is lined with non-combustible material, for example, asbestos.

When attaching to a concrete or brick wall, special aprons are used. Then we bring the end of the horizontal pipe through the wall and mount the tee there, necessary for vertical pipe. It is necessary to install the brackets on the wall after 2.5 m.

The next step is to mount, lift the vertical pipe and bring it out through the roof. The pipe is usually assembled on the ground and the mount for the brackets is prepared. The fully assembled volumetric pipe is difficult to install on the elbow.

To simplify, a hinge is used, which is made by welding pieces of sheet iron or cutting a pin.Typically, the vertical pipe is inserted into the tee pipe and secured with a pipe clamp. The hinge is attached to the knee in a similar way.

After raising the pipe in a vertical position, the pipe joints should be bolted where possible. Then you should unscrew the nuts of the bolts on which the hinge was fastened. Then we cut or knock out the bolts themselves.

Having selected the hinge, we attach the remaining bolts in the connection. After that, we stretch the remaining brackets. We first adjust the tension manually, then we fix the cable and adjust it with screws.

Necessary distances to be observed when the chimney is located outside

The installation is completed by checking the chimney draft. To do this, bring a burning piece of paper to the fireplace or stove. Draft is present when the flame is deflected towards the chimney.

The figure below shows the distances that must be observed in various options for the location of the chimney from the outside:

• when installed on a flat roof, the distance must not be less than 500 mm;
• if the pipe is removed from the roof ridge to a distance that is less than 1.5 meters, the height of the pipe must be at least 500 mm in relation to the ridge;
• if the chimney outlet installation is located at a distance of more than 3 meters from the roof ridge, then the height should not be more than the expected straight line.

The setting depends on the type of duct directions required for the combustion of the fuel. In the interior of the room, there are several types of directions for the chimney channel:

Support bracket for chimney

• direction with a rotation of 90 or 45 degrees;
• vertical direction;
• horizontal direction;
• direction with a slope (at an angle).

It is necessary to install support brackets for fixing the tees every 2 meters of the smoke channel, it is necessary to provide additional wall mounting. In no case, when installing a chimney, horizontal sections higher than 1 meter should not be created.

When installing chimneys, consider:

• the distance from metal and reinforced concrete beams to the inner surface of the chimney walls, which should not exceed 130 mm;
• the distance to many flammable structures is at least 380 mm;
• cuttings for non-combustible metals are made for the passage of smoke channels through the ceiling to the roof or through the wall;
• the distance from combustible structures to an uninsulated metal chimney must be at least 1 meter.

Gas chimney connection boiler is based on building codes and manufacturer's instructions. The chimney requires cleaning up to four times a year (see How to clean a chimney).

In order to optimally calculate the height of the chimney, it is necessary to take into account the type of roof and the height of the building:

• the elevation of the chimney pipe must be at least 1 meter when installed on a flat roof and at least 0.5 meters above a non-flat one;
• the location of the chimney on the roof must be made at a distance of 1.5 meters from the ridge;
• the height of an ideal chimney has a height of at least 5 meters.

footage

The ratio of affordable price, ease of installation, long working life and efficiency made coaxial pipelines very popular. If you also decide to give preference to just such, be sure to follow the installation rules given in the article.

Options for gas ducts for a country house

To discharge combustion products with a relatively low temperature (up to 120 ° C) emitted by gas boilers, the following types of chimneys are suitable:

• three-layer modular stainless steel sandwich with non-combustible insulation - basalt wool;
• a channel made of iron or asbestos-cement pipes, protected by thermal insulation;
• ceramic insulated systems such as Schiedel;
• brick block with a stainless steel pipe insert, covered from the outside with heat-insulating material;
• the same, with an internal polymer sleeve of the FuranFlex type.

Three-layer sandwich device for smoke removal

Let us explain why it is impossible to build a traditional brick chimney or put an ordinary steel pipe connected to a gas boiler. The exhaust gases contain water vapor, which is a product of the combustion of hydrocarbons. From contact with cold walls, moisture condenses out, then events develop as follows:

1. Thanks to numerous pores, water penetrates into the building material. In metal chimneys, condensate flows down the walls.
2. Since gas and other high-efficiency boilers (on diesel fuel and liquefied propane) operate periodically, frost has time to grab moisture, turning it into ice.
3. Ice granules, increasing in size, peel the brick from the inside and out, gradually destroying the chimney.
4. For the same reason, the walls of an uninsulated steel flue closer to the head are covered with ice. The passage diameter of the channel decreases.

Ordinary iron pipe insulated with non-combustible kaolin wool

Selection Guide

Since we initially undertook to install an inexpensive version of the chimney in a private house, suitable for do-it-yourself installation, we recommend using a stainless steel pipe sandwich.Installation of other types of pipes is associated with the following difficulties:

1. Asbestos and thick-walled steel pipes are heavy, which complicates the work. In addition, the outer part will have to be sheathed with insulation and sheet metal. The cost and duration of construction will definitely exceed the assembly of a sandwich.
2. Ceramic chimneys for gas boilers are the best choice if the developer has the means. Systems such as Schiedel UNI are reliable and durable, but too expensive and out of reach for the average homeowner.
3. Stainless and polymer inserts are used for the reconstruction - lining of existing brick channels, previously built according to old projects. Specially fencing such a structure is unprofitable and pointless.

Flue variant with ceramic insert

Turbocharged gas boiler is also possible connect to a conventional vertical chimney, organizing the supply of outside air through a separate pipe. The technical solution should be implemented when a gas duct has already been made in a private house, brought to the roof. In other cases, a coaxial pipe is mounted (shown in the photo) - this is the most economical and correct option.

Noteworthy is the last, cheapest way to build a chimney: make a sandwich for a gas boiler with your own hands. A stainless pipe is taken, wrapped in basalt wool of the required thickness and sheathed with galvanized roofing. The practical implementation of this solution is shown in the video:

Chimney of solid fuel boiler

The mode of operation of wood and coal heating units involves the release of hotter gases. The temperature of the combustion products reaches 200 ° C or more, the smoke channel warms up completely and the condensate practically does not freeze.But it is replaced by another hidden enemy - soot deposited on the inner walls. Periodically, it ignites, causing the pipe to heat up to 400-600 degrees.

Solid fuel boilers are suitable for the following types of chimneys:

• three-layer stainless steel (sandwich);
• single-wall pipe made of stainless or thick-walled (3 mm) black steel;
• ceramics.

Brick gas duct of rectangular section 270 x 140 mm is lined with an oval stainless pipe

It is contraindicated to put asbestos pipes on TT-boilers, stoves and fireplaces - they crack from high temperatures. A simple brick channel will work, but due to roughness it will become clogged with soot, so it is better to sleeve it with a stainless insert. Polymer sleeve FuranFlex will not work - the maximum operating temperature is only 250 ° C.

Types of coaxial chimneys

Depending on the method of laying the chimney, coaxial chimneys are divided into two types:

1. Vertical - the chimney is located strictly in a vertical position. Gases and combustion products rise from the fuel chamber and are released into the atmosphere above the level of the ridge. Mostly vertical structures are used in residential buildings and provide a good level of natural draft.
2. Horizontal - the main channel of the chimney is represented by a structure located in a horizontal position, which is removed through a load-bearing wall. In this case, flue gases go outside in the immediate vicinity of the heating equipment. It is more often used in private houses where closed-type heating systems are installed.

A vertically oriented coaxial chimney, despite some advantages, is a more expensive and difficult to install system. The total length of the chimney channel usually exceeds 5 meters, which greatly complicates the process of installation and fixing the structure.

For the manufacture of a coaxial type chimney, various grades of steel and plastic are used. In accordance with this, several types of chimneys can be distinguished:

• galvanized - the most affordable option for a coaxial type chimney. The average service life of the product does not exceed 5–7 years, after which the structure partially rusts or is damaged. The cost of the product depends on the manufacturer and technical parameters, but rarely exceeds 2–2.5 thousand rubles;

• made of plastic and aluminum - a combined option for private use. The internal channel of a flue is made of aluminum up to 2 mm thick. The outer tube is made of high-strength heat-resistant polypropylene. Such chimneys are used only in the private sector to work with boilers of small and medium power;

• stainless - more reliable and durable chimneys than galvanized ones. They are designed for 10-12 years of use. The cost is almost the same as stainless steel products. In industry and collective chimney systems are not used, since the "stainless steel" does not withstand high concentrations of chemicals;

• made of high-alloy steel - the most durable and durable version of the coaxial chimney. High alloy steel is not afraid of high temperatures and chemicals contained in flue gases. The average service life is at least 15 years.

In the line of some manufacturers (Electrolux, Viessmann, Schiedel) there are models of coaxial chimneys with an additional heat-insulating layer. This is a classic design with two channels, which is located in another pipe. The voids between the outer tubes are filled with non-combustible heat-insulating material, which prevents freezing and blockage of the air channel.

How to check and adjust the draft in the chimney of a gas boiler

Thrust is a reduction in pressure at the place where the fuel is burned. The pressure reduction occurs due to the removal of combustion products through the smoke channel. Speaking within the framework of this article, the draft forces fresh air to enter the combustion chamber, where there is a reduced pressure that occurs due to the fact that the products of combustion of the gas are removed to the outside.

The presence of draft indicates that the chimney is designed and installed correctly, and the equipment is working properly. Lack of draft may be a direct or indirect confirmation of the need for preventive maintenance or repair of equipment and the smoke exhaust system.

To check the level of traction, the following methods are used:

• visual inspection - in the room where the heating equipment is located, there should be no smoke;
• use of improvised means, for example, a sheet of paper. It is brought to the viewing hole. If there is traction, then the sheet will deviate towards the hole;
• measurement with a special device - anemometer. It is used to control the air speed.

For traction control, it is better to use the latter method, since only it will show the exact value. When measuring natural draft, the flue gas velocity should be in the range of 6–10 m/s.The value is taken from SP 41-104-2000 "Design of autonomous heat supply sources".

If this does not help, then the only way out is to replace the chimney with a preliminary calculation of the cross section of the chimney. At the same time, it is desirable to minimize the number of rotary elements or even remove them altogether.

Why does the boiler blow out and how to fix it

The main reason why the burner blows out in the boiler is the backdraft effect that occurs due to problems with the chimney.

Before proceeding with any measures, you should check the height of the chimney above the level of the ridge and the presence of an installed deflector, which allows you to reduce the penetration of wind flows into the chimney. If the pipe device is not made according to the rules, then after the steps described below, you will need to build up the pipe and install a deflector.

In order to solve the problem with blowing the boiler, you will need to do the following:

1. First of all, it is necessary to check the level of draft in the pipe. For better use an anemometer. If it was not possible to find it, then with the boiler running, you need to lean the paper against the outlet of the chimney. If the sheet is attracted to the chimney, then there should be no problems with draft.
2. If it was found that the blowing is due to a loss of natural draft, then it will be necessary to check the chimney connection points. For this, a thermal imager is used. If the pipe passes air, then the device will show a strong temperature difference between the main pipe and the junction of the two modules.
3. If the chimney is assembled correctly, then it is necessary to clean the smoke channel using a cable with a nozzle. The diameter of the nozzle is selected according to the section of the chimney pipe.An inspection hole at the bottom of the chimney is used to clean soot, tar and other combustion products.
4. After performing these simple steps, you will need to check the level of traction again. If the natural draft has not improved, then it is necessary to carry out work to correct the height of the chimney and install a deflector. During installation, a heat-resistant sealant and crimp collars are used.

In cases where the work described above did not produce results, contact the gas service with the aim of gas equipment checks. Perhaps the problems with blowing are associated with ultra-sensitive automation.

Video: how to check draft in a gas boiler

Compliance with regulatory requirements is a guarantee that during the operation of the chimney there will be no emergency situations. This is especially true for vertical chimneys, when it will take a lot of time to correct the mistakes made during their installation.

Device and purpose

Such a chimney consists of two pipes having different diameters. It is made of pipes, which is smaller, inserted into another so that there is a gap of several centimeters between them. Such a device of the chimney system allows you to remove the products of combustion, and at the same time draw the right amount of air from the street. That is, constant circulation is ensured. Also in the design of coaxial systems, a “knee” is used, which is a transitional element, and a clamp that securely fastens all parts of the structure.

It is also worth highlighting two main types of systems, depending on the design features, in which such chimneys can be installed:

1. collective systems.Such types of chimneys are installed during the construction of large high-rise buildings.
2. individual systems. This type of system is used for installation in private homes where one heater is used.

Boiler structures and chimney outlet

Structurally, a gas boiler is a device consisting of a gas burner, to which gas is supplied through the nozzles, and a heat exchanger, which is heated by the energy obtained during the combustion of gas. The gas burner is located in the combustion chamber. The movement of heat occurs with the help of a circulation pump.

In addition, modern types of gas boilers are equipped with various self-diagnosis and automation modules that allow the equipment to be used offline.

When choosing a chimney, pay attention to the type of combustion chamber of the boiler. It is from its design that the method of air intake required will depend for gas combustion, and as a result, the optimal type of chimney

Different types of chimneys are suitable for different types of combustion chamber

The combustion chamber for gas boilers is of two types:

• open - provides natural traction. The air is taken from the room where the heating equipment is installed. The removal of combustion products is carried out by means of natural draft using a chimney with an exit through the roof;
• closed - provides forced draft. The intake of air for combustion of fuel occurs from the street. In rare cases, air can be taken from a special room equipped with forced ventilation. For the simultaneous removal of flue gases and intake of fresh air, a coaxial type chimney is used, which is led out through the nearest load-bearing wall.

Knowing the type of combustion chamber, you can easily select or make a chimney that is suitable for the design. In the first case, when the boiler is equipped with an open combustion chamber, a conventional thin-walled or insulated chimney is used.

For boilers with a closed combustion chamber, a coaxial chimney is used, which is a structure consisting of pipes of different diameters. A pipe with a smaller cross section is fixed inside a pipe with a larger diameter by means of special racks. Through the inner channel, carbon dioxide and other combustion products are removed, and through the gap between the outer and inner pipes, fresh air enters the closed combustion chamber.

Methods for installing chimneys

According to the method of installation, chimneys are divided into:

• internal - chimneys made of metal, brick or ceramics. They are both single-walled and insulated double-walled structures. Arranged vertically upwards. Perhaps the presence of several knees with an offset of 30o;
• outdoor - coaxial or sandwich chimneys. They are also located vertically upwards, but the chimney is brought out horizontally through the load-bearing wall. After the pipe is removed, a 90° swivel elbow and support brackets are installed to allow installation in the desired direction.

The chimney can be led outside through the wall in close proximity to the boiler or traditional way through the roof

When choosing a chimney device, the dimensions of the building in which the equipment is located should be taken into account. For small buildings, it is more advisable to use external chimneys, as they allow you to bring the chimney outside the room.

In other cases, one should build on personal capabilities. If space permits and it is possible to perform high-quality insulation in the places where the pipe passes through the floors, then an internal chimney will be the best solution. Especially if the structure is lined with brick or protected by a ceramic box.