The structure of the furnace chimney. How to make a chimney (chimney) out of bricks with your own hands? Specifications of sandwich pipe

The flue is an important part of the heating devices working on gas, solid or liquid fuel. In fireplaces, stoves, saunas and boilers, it is important to maintain a certain level of draft in order to purify the air from combustion products. The correct choice of the chimney pipe is the basis for the safe operation of the heater. Errors in the construction of the chimney can lead to life-threatening situations.

Chimney pipes are made of metal, ceramics and bricks. Metal pipes are currently in the greatest demand. Of all the varieties of this material, it is recommended to choose steel. Steel pipes for chimneys are coated with special solutions that make the material resistant to all adverse effects of the internal environment of the chimney.

When choosing a pipe, it is necessary to take into account the parameters of heating devices and the fuel used. The material from which the pipes are made must withstand higher temperatures than the fuel can create.

When using some types of heating devices, chemically active substances come across among the incompletely oxidized combustion products. They can damage the chimney, which is not sufficiently resistant to chemicals. Some unburned particles can ignite, creating sparks. Therefore, the material from which the pipe is made must be refractory.

It is interesting! When choosing a pipe, it is necessary to pay attention to the melting point of the material from which it is made. The melting temperature of steel exceeds 1000 0C - the highest possible indicator encountered in the operation of coal-fired heating appliances.

The advantages of steel pipes are:

Ease of installation. Steel pipes do not require the installation of a special foundation, they do not require complex engineering solutions or special installation tools. You can install them yourself without prior preparation. Due to the plasticity of the material, complex technical structures can be created.
Light weight. It is easy to transport, lift and move them independently without a team of workers, which also simplifies installation.
Resistant to high temperatures. Steel products are suitable for appliances that run on any fuel. They do not melt at maximum temperature loads.
chemical inertness. Steel does not interact with chemicals that can be formed as under-oxidized combustion products. These substances are not capable of destroying it.
Corrosion resistance. This advantage applies to specially coated pipes and stainless steel. The material itself corrodes quickly. It should be borne in mind that in addition to the internal environment, external adverse factors, such as precipitation, affect the chimney pipe. Preference should be given to coated pipes.
Smooth inner walls. On a rough surface, combustion products settle, turning into soot, gradually reducing the clearance. This reduces the draft in the chimney. Steel is completely smooth, the risk of soot settling on their surface is minimal.

The device of the chimney, knowledge of the main advantages and disadvantages of different types of chimney and materials for the construction of pipes - this knowledge is necessary for novice home craftsmen before installing the stove in the house. The installation site and the set of tools and materials for the work depend on the choice of design and materials.

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Furnace chimney device

Depending on the material for the manufacture of the chimney, you will need to prepare and make different individual parts. General - this is an air damper to adjust the amount of draft in the chimney and a protective visor at the top of the pipe.

It is necessary to protect the internal channel from water or snow. The rest of the details of different types of chimney are radically different. Let's analyze the main ones in more detail.

Brick chimney

Such chimneys are installed only for laying indoors, through the roof and floor slabs. It is not recommended to lay out brick structures in multi-storey buildings.

Diagram of a brick chimney for a furnace

Partitions on different floors can be displaced, you will have to perform horizontal layering, which is almost impossible to do on such structures. A brick chimney consists of several main parts:

oven neck. This square or rectangular structure emerges from the furnace body and runs throughout the building. In the lower part, several grooves are made to clean the channels from debris and soot. A thin cavity is laid out above the furnace body for installing an air damper. With its help, the thrust force (the upward flow of air) necessary for the normal operation of furnaces and boilers is regulated;
at a certain distance from the floor slab, the bricklayer begins to lay out the pipe fluff. The internal size remains unchanged, and outside they begin to push the bricks to a third of the length of the brick. The outer dimension, at the widest point of the fluff, exceeds the inner minimum by 600-700 mm. On the 9th row, the neck of the pipe is laid out. This detail allows you to lower the temperature of the exhaust gases and serves as a kind of compensator for the entire structure. Fluff is laid out in front of each floor slab;
"Otter" - this part of the chimney is laid out before the pipe passes through the roof surface. For its masonry, 7 rows will be needed. By 6, the outer dimension gradually increases while maintaining the inner one; by 7, the size is reduced to the main one and the neck of the pipe is placed;
The head is the last 2 rows of bricks that are exposed outside, increasing the outer size by 60-70 mm. this design prevents precipitation from entering the chimney, but to completely block the channel, it will be necessary to install a protective visor or cap.

Chimney made of sandwich pipes

For such a chimney, several parts are used:

Chimney outlet schemes

There are 2 main schemes for laying a chimney:

Schematic representation of the chimney output options:

Schemes of options for outputting a chimney

It makes no sense to describe them in detail - these are topics for separate articles, which can be read below:

Which device option to choose?

If you want to equip a chimney for a stove in an apartment on the 2-3rd floor, the unambiguous solution to this problem is to lay pipes from the outside and bring them out through the wall. In this embodiment, we do not have to perform possible horizontal segments that make it difficult to clean soot from pipelines and reduce traction.
For furnaces or boilers running on gas, we reduce the cross section of the inner plane. For solid propellant equipment, this size should be much larger.

Fundamental rules:

The minimum chimney diameter for wood-burning stoves is 115 mm. Coaxial piping, carried out outside cope with their task. External pipelines, like internal ones, are covered under a layer of thermal insulation. But the best option for outdoor chimney laying is to use sandwich pipes.
The inner lining is used when installing a brick chimney or when equipping a private household. In this option, the laying is carried out through the floor slabs and the roof structure. To insulate a brick pipe in these places, they are covered with sheets of thermal insulation or special boxes are made, making an internal cavity for the passage of the pipe a little larger than its dimensions.
Installation of steel sandwich pipes is carried out using mounting couplings and fittings. All rules and recommendations for conducting chimneys are collected in SNiP 2.04.05 dated 91. This document indicates how to lay the chimney of a bathhouse, country houses or apartment buildings. All the necessary clearances, recommendations on the length and cross section of pipes are given here.

Which chimney is better, brick or metal?

No one can give you a definite answer to this question. The main thing is the height and size of the chimney. Its minimum size is from 5 m. If you make it short, there is a high risk of back draft and exhaust gases escaping into the room.

Regardless of the material, if it is warmer outside than indoors, the draft will become weaker or even disappear when the outdoor part heats up more than the air in the house.

A brick or metal chimney and the level of draft in them are negatively affected even by nearby trees or mountain slopes. The wind creates backwater, and traction can drop significantly.

Excessive air flow in the furnace will also not bring the furnace to normal operating conditions. Such a pressure can cause a strong heating of the furnace parts and their deformation. And the heat will simply be blown out of the furnace, it will not have time to heat the walls of the furnace.

Conclusion

The materials of the chimneys do not have any effect on the performance of the heating system. But on brick pipes with rough surfaces, a layer of soot forms faster, and drops of condensate appear on the steel walls of poorly insulated pipelines.

Long breaks in work adversely affect the condition of the brick oven and do not have any effect on steel ones. The main thing in this matter is the quality of materials and the correctness of calculations and installation of chimneys.

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The chimney is one of the most important elements of the entire structure of the house, especially for devices such as stoves, heating boilers, fireplaces, gas water heaters. The purpose of chimneys is to remove the product of combustion in a safe way, ensuring the cleanliness of the air in the room, freshness, and safety. In addition, the normal operation of such devices also depends on how well the chimney is designed, what material it is made of, what are the conditions for its operation. At the same time, the question of how to properly make a chimney is one of the most important.

The chimney is one of the most important safety features of the whole house.

In our article, we will consider what types of chimneys are, what materials they can be built from and in what way, we will learn about the requirements for such a system and installation.

Types of chimneys

Today, the installation of a wide variety of types of chimney pipes is used, which may have different characteristics. Some of them are very cheap and easy to install even with your own hands, but there are also more expensive, complex systems, the installation of which requires the participation of specialists.

Among these types of chimneys, it is necessary to highlight the following:

Brick, which are the most popular. This is the traditional way of arranging a pipe, which is most often found in large estates and old houses.
Steel chimneys, often stainless steel, although galvanized steel may also be used. Recently, pipes made of acid-resistant steel with molybdenum additives have become in demand.
Ceramic chimneys are a complex structure made of ceramic, steel or concrete layer.
Other materials such as glass, fireclay, etc.

In addition, chimneys can be divided into:

mounted, that is, installed on furnaces, this is the most used method;
indigenous, that is, free-standing near furnaces;
wall, passing through the main walls of the house.

Recently, coaxial chimneys have been made, arranged according to the “pipe in pipe” principle.

But they are used in the household very rarely. They work as follows: outside air is taken in through the outer pipe, and all combustion products are removed through the inner pipe. Installing such a chimney for a private house allows you to do without an additional ventilation system, which is very beneficial.

Chimney Requirements

Chimney draft must be monitored at all stages of installation.

When asked how it is right, you must follow these requirements:

any design must comply with SNiPs;
only one device is connected to one channel, but in rare cases two are allowed, the distance between them should not be less than 7.5 meters;
the chimney must be airtight, leakage of combustion products is unacceptable in any case;
it is necessary to provide protection against condensate during the device, which can drain along the inner walls, damaging the pipe material;
installation should provide for careful control of traction;
the outlet of the chimney should always look only at the sky; no covers, visors, etc. can be installed above it.

Chimneys: from asbestos to brick

A modern chimney can be made from a wide variety of materials; ceramic and glass pipes are no longer surprising, which do their job much better than traditional brick ones. Consider individual types of pipes, options for their device, advantages.

Asbestos cement pipes

Asbestos-cement pipes are considered the most economical.

A couple of decades ago, asbestos cement chimneys were the most popular, this material was extremely cheap. Their installation is possible for stoves, fireplaces, heating networks. But of the pluses, only the low price can be noted, otherwise, this is far from the best option. The fact is that the maximum temperature of the combustion products can be only 300 degrees, which is often simply not enough.

Of the shortcomings, the following should be noted:

installation only for vertical sections;
difficult installation, since the weight of the pipe is large;
the joints of such a chimney are not airtight, which is simply unacceptable for a private house;
condensate is absorbed into the walls of such a pipe, which makes them of poor quality;
high unreliability and danger - pipes burst at high temperatures;
almost everything can be connected to an asbestos chimney, but boilers require tees, cleaning hatches, and steam traps.

Steel chimneys

How to install a chimney so that it is simple and reliable? The answer is simple: steel chimneys are not only very durable and reliable, but also relatively easy to install. But even here there are some nuances: simple steel products are subject to corrosion, their service life reaches only 3-4 years. Therefore, it is recommended to take galvanized pipes, stainless steel chimneys.

These pipes provide:

tightness;
simple maintenance;
excellent traction due to the smooth inner surface;
overcoming the threshold of condensate formation;
fire safety;
relatively easy installation.

Of the minuses, it should be noted that metal chimneys are expensive, the design often requires the presence of a specialist, in many cases insulation is required, that is, a sandwich pipe is made.

brick structures

Brick chimneys have always been the most popular in the construction of brick houses.

Brick chimneys, which are often installed on the roof, are traditional. They are not only attractive, but also functional, but they are categorically not suitable as a flue! The fact is that under the influence of condensate, the brick collapses very quickly, it absorbs moisture, and at the same time spoils the interior decoration of the walls. If you make such a chimney without preparation and special knowledge, then it can become very dangerous!

When installing, it is necessary to comply with quite a few requirements, one of which concerns the height of the pipe, more precisely that part of it that protrudes above the roof. The height depends on the distance that exists between the pipe and the ridge. Of the requirements, it is necessary to note the following:

installation of a brick chimney is possible only if its walls are at least 10 cm;
above and below the passage of the roof by about 15 cm in the chimney there should not be any joints, which is important for ensuring safety;
the cross-sectional area of the channel should not change throughout the entire length, as this may adversely affect the thrust;
when choosing the type of brick, it is necessary to take into account the temperature of the combustion products, the power of the thermal device, the installation scheme;
the bend should not be more than 30 degrees.

Fireclay pipes

For several years, chimneys made of such material as fireclay have been offered on the market. Their shell is made of concrete or steel, the inner tube is made of ceramics. Such systems have already gained popularity due to their reliability. The cake of such a chimney consists of the following layers:

internal fireclay (ceramic) pipe for the removal of combustion products and gases;
special insulating layer of basalt wool;
the outer casing of the system is made of steel or lightweight concrete (foam concrete).

Of the minuses, it should be noted that the price is quite high, but it fully pays off with simple installation and the highest quality and reliability.

One of the main components in the heating system is the smoke outlet. The installation of a chimney in a private house is a rather complicated and important process, since not only the proper functioning of the heater, but also the health of the residents of the house depends on the correct operation.

Boiler chimney device in a private house

The functions of the chimney are to remove harmful products that are released during the combustion of fuel along with smoke, so at least some of these substances cannot be allowed to seep into the room.

Another, no less important, factor in the arrangement of the chimney is its fire safety. It is necessary to ensure its correct passage through ceilings and roofs, as well as to isolate it from walls built of combustible materials. By observing all the rules when building this heating communication, you can achieve its excellent work for many years, of course, by conducting annual preventive maintenance.

Everything must be done so as not to get further problems with regulatory organizations, as well as feel completely safe, and for this it is worth studying the mandatory rules and regulations for the construction and operation of chimneys for heating appliances. This is especially true of brick ovens and fireplaces.

The oven must have its own foundation. This condition is important because this structure should not depend on other foundations of the house. In the event of shrinkage or other unforeseen movements of the soil, the skew of the common foundation can lead to a violation of the masonry not only of the furnace, but also of the chimney. The appearance of seemingly minor and imperceptible cracks can pose a serious threat to the health of residents.
The blower hole must be at a height of at least ten centimeters from the floor, as it must provide a sufficient supply of oxygen, thereby ensuring the normal combustion of fuel and draft in the chimney.
For fire safety purposes, the stove must be located at least 25 centimeters from the walls of the building, made of flammable materials. And the best option would also be to isolate the walls with heat-resistant materials.
When arranging the internal structure of the furnace, where the chimney with flue channels actually begins, it is necessary to strictly observe the layout of the rows. Overlapping at least one of the channel openings can threaten the house with smoke, with all the ensuing consequences.
The furnace body itself should be 35–40 centimeters below the ceiling. Next comes the chimney.
It is very important to arrange the correct cutting of the chimney passage through the attic floor. Brick protrusions should have steps seven centimeters high before entering the ceiling and after cutting out in the attic.
If the attic floor is insulated with combustible heaters, it is imperative to lay a sandy layer of at least five to seven centimeters on top of them.
During fire cutting in the attic, the distance from the inner wall of the chimney to combustible materials must be at least 50 cm. For this, the chimney skirt is laid out, which is located directly in the attic floor.
The wall thickness of the brick chimney pipe should be 12-15 centimeters.
If the pipe comes out on the roof at a distance of more than three meters from the ridge horizontally, its height should be no more than 10 degrees in slope from the horizon. If the pipe is located at a shorter distance, it must rise above the ridge by at least half a meter.
These rules are provided by fire safety services and must be strictly observed.

Chimney for metal furnaces and boilers

Chimneys for cast iron stoves are simpler in structure and come in two types:

The first of them, shown in the figure, is more complicated than the second in execution, since it passes through all the ceilings inside the building. Particularly laborious will be the procedures for arranging it in the roof and waterproofing the seams around the pipe.

But the advantage of this chimney is that it retains more heat in the rooms and that it can also heat the second floor or attic through which the pipe will pass.

The second option for a metal stove chimney is a structure that runs almost completely along the street. Only part of it remains inside the house, which is fixed horizontally. This is a cut off from the heating device, which can be straight or in the form of a so-called knee. It exits through the wall to the street and enters a vertical chimney that rises parallel to the wall. Such a device is safer, and the pipe will not take up extra space in the room. Its arrangement will not cause trouble for waterproofing on the roof and for its passage through the floors.

But, making such a design, the pipe for it must be chosen with a thicker heat-insulating layer, which can reach a thickness of up to 10 cm. Without such insulation, the smoke in the pipe will quickly cool, the draft will decrease, and condensation may also form, which is highly undesirable for the furnace .

Details for a metal chimney

If earlier, in order to make a decent chimney, you had to tinker a lot or spend a considerable amount on an order for a tinsmith, today manufacturers of ventilation and heating systems produce finished parts of various configurations.

Such chimneys are produced for different diameters, heights and thicknesses of insulation. In addition, other accessories are sold that are necessary for installing a chimney system on the wall and protecting it from moisture ingress. An approximate list of parts intended for this purpose:

Pipes of different lengths, equipped with special locking grooves for fastening them to other structural parts.
Metal corner transitions, made at different angles.
Clamps in various sizes.
Mounting brackets
Floor, wall and ceiling stands and pipe fittings.
Tees, also made at different angles.
Deflectors, fungi, spark arresters and thermofungi.
Connecting bends with the required range of angles.
Other small parts needed to install the chimney.

Important components in the chimney device

It is very important to correctly arrange the most complex components of the chimney - its passages through the attic, interfloor ceiling, roof, and also through the wall if the main pipe runs completely along the street.

Interfloor and attic flooring

The most difficult thing is to correctly lay pipes through ceilings, walls, roofs

Framing the passage of the chimney in the ceiling, made of wood, is carried out with special nozzles that isolate it from combustible materials in order to prevent their ignition. The branch pipe has a larger diameter than the pipe, so when they are connected, a gap is formed, which also helps to protect against overheating.

Chimney passage through the ceiling

There must be a distance between the chimney and the ceiling in which it is necessary to place a foil or asbestos non-combustible material, the thickness of which must be at least 7-9 cm. The foil insulator is laid with foil inside.

The pipe is solid. The passage through the wooden ceiling is covered with a metal flange

It is important to remember that in the place of the passage in the ceiling, the pipe cannot have joints, but must be solid.

Same thing on the floor

If a pipe is planned to pass in the room of the upper floor, then a casing should be arranged around it, with ventilation holes through which hot air will enter the room. They are usually drilled from the top and bottom of the casing. Such protection is needed in order not to accidentally burn yourself on a very hot pipe during the heating of the furnace.

On the ceiling and on the floor of the second floor, at the place where the pipe passes through the floors, there are metal parts of the flange pipe that cover the combustible materials of the floor and ceiling.

Passage through the wall

The passage of the chimney through the wall is made in the same way as through the ceiling, with the help of special nozzles put on the chimney, which will help isolate combustible materials from high temperatures. Also, the section of the pipe that will be in the wall is wrapped in heat-resistant material with a thickness of at least 7-10 cm.

Passage through the roof

The most difficult place is the node of penetration through the roof of the pipe. It requires special attention in work, since the safety of the crate and insulation from external moisture, as well as the overall fire safety of the house, will depend on it.

To do this, waterproofing is arranged around the pipe from the outside with the help of a special tape or “passage” on the flange, which are fixed to the adhesive-sealant, and screwed on top with self-tapping screws.

Particular attention - thermal insulation of the roof structure

To prevent overheating of the crate, the pipe must be wrapped with heat-resistant material, and pass through the metal panel from the inside of the roof.

The final step in installing the chimney is to install an umbrella on top of it, which will prevent dirt and water from getting inside.

Conditions for normal operation

The design must:

effectively remove gaseous wastes of fuel combustion;
be safe and comfortable at home;
have good traction;
withstand high temperatures;
be protected from moisture and condensation;
have resistance to external aggressive environment.

Chimneys can have a square and cylindrical shape, the latter is considered optimal, as it is less susceptible to the accumulation of soot and soot.

Other parameters that are also indicated by building codes:

alloy steel parts produced for the installation of chimneys are distinguished by their anti-corrosion properties and have a thickness in in 0.5 cm;
the size of the pipe diameter must match the size of the furnace nozzle or be slightly larger than it;
a chimney arranged for a brick oven is equipped with pockets that are located at the bottom of the chimney channels and have a depth of 20-25 centimeters. Doors are installed on them through which cleaning from soot deposits is carried out;
a metal chimney cannot have more than 3 turns;
the turning radius of a metal chimney cannot be greater than the diameter of the pipe;
the pipe must have a height of at least five meters.

All these conditions will help to create normal draft in the chimney and effective removal of combustion products hazardous to health.

A small video tutorial on installing a chimney in a private house

It must be remembered that the choice of a chimney does not depend on its external data, but on the furnace on which it will be installed, as well as on the fuel used and other heating parameters. Therefore, before purchasing or constructing a chimney, it is necessary to consult a specialist.

And one more warning - for some inexperienced builders, the abundance of requirements for the arrangement of stove heating and chimneys - in particular, may seem like unnecessary "nitpicks" that you can, if you wish, ignore. Believe me, these rules have been developed by life itself, based on centuries of experience and careful engineering and technical calculations. It is sad, but more than once the neglect of them has been paid for with human lives.

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A do-it-yourself chimney for a stove can be erected if there is a masonry scheme at hand, and the home master himself has at least minimal skills in the work of a bricklayer. The construction of this department requires no less serious approach than, since the efficiency of heating, the safety of those living in the house, and the overall life of the entire heating structure will depend on the quality of its masonry.

When working on a chimney, it must be remembered that its internal surfaces must be as neat and even as the external ones, since this factor directly affects the creation of good traction.

Varieties of brick chimneys

Chimney pipes are divided into types depending on the location of their installation relative to the furnace itself. So, they are root, mounted and wall.

The most common design of a brick chimney is a wall-mounted one. It is installed directly on top of the heater and is its continuation. Such chimneys are often installed during the construction of a heating or bath stove.

The second most popular is the root chimney. This type of pipe is distinguished by the fact that it is installed next to the furnace or is included in its design and is placed on one of its sides.

Root pipes can be installed for both brick and cast iron stoves. In addition, one root structure is often used for several heaters. For example, in a two or three-story house, one chimney is passed through all floors and furnaces are connected to it. If it is planned to use the pipe in this way, then in this case, an accurate calculation of its parameters must be made, otherwise there will be no normal draft, which means that the efficiency of the furnaces will also decrease, and the risk of combustion products entering the premises will increase.

The wall pipe is built into the main internal or external walls. But, in the latter case, the walls of the chimney will have to be very well insulated, since due to the large difference in external and internal temperatures, condensate will actively collect inside the duct, which will significantly impair the operation of the furnace, reducing draft and contributing to the rapid growth of the chimney with soot.

It should be noted that although this structure is distinguished by a separate type, it can be both root and mounted.

Construction of a brick chimney

The chimney has several sections. To understand its fundamental design, we can take the structure of a packed pipe as an example, since most often it is the design engineers who choose it when drawing up furnace ordering schemes.

So, the design of the extension pipe with its passage through the attic floor and the truss system includes the following departments and elements:

1 - Metal cap or umbrella. It can have a variety of forms, but its function is always to protect the interior of the chimney from the penetration of various types of precipitation, as well as dust and dirt.

2 - The head of the pipe consists of bricks protruding outward, which will protect the neck of the structure from raindrops that will flow down the protective cap. The metal umbrella is fixed, including on the protruding parts of the head.

3 - The neck of the pipe.

4 - Cemented or otherwise waterproofed inclined surface of the otter, designed to drain water that has fallen on the neck of the pipe.

5 - Otter. This part of the structure has thicker walls than the pipe neck. The otter should be located at the point where the chimney passes through the rafter system and the roof. The thick walls of the otter will protect the combustible materials of the crate under the roof from overheating.

6 - Roofing material.

7 - Lathing of the truss system.

8 - Rafter.

9 - Pipe riser. This department is located in the attic of the house.

10 - Fluff. This part of the chimney starts under the ceiling inside the house, passes through the attic floor and ends in the attic, just above or flush with the floor beams. The fluff, like the otter, has thicker walls than the neck and riser of the pipe. The increased thickness also protects wooden beams and other combustible materials of the attic or interfloor floor from overheating.

It should be noted that in some cases, instead of fluffing in its place, a metal box is mounted around the pipe, filled with non-combustible materials, such as sand, vermiculite or expanded clay. The functions of this layer, having a thickness of 100 ÷ 150 mm, are also the protection of combustible floor materials from overheating.

11 - Floor beams.

12 - Insulation, which is most often made from asbestos, is in any case necessary to create fire safety, since the walls of the chimney will come into contact with the wood of the floor beams and other materials that make up the floor and ceiling.

13 - Smoke damper, located in the room, in the upper part of the pipe, which allows you to adjust the intensity of the discharged streams of heated air and combustion products.

14 - The neck of the pipe, which begins at the top of the furnace - the ceiling.

Calculations of the parameters of the chimney pipe

The principle of operation of the chimney system is the movement of air masses from the combustion chamber to the exit to the street, that is, from the lower point to the upper one. This process occurs through the creation of traction, which occurs due to temperature and pressure changes. It is thanks to all these factors that the normal functioning of the chimney system is carried out.

To create optimal aerodynamic processes, the size of the pipe channel must correspond to the power of the furnace, which, in turn, largely depends on the size of the furnace. The surfaces of the internal chimney space must have smooth walls, along which the air flows will slide freely without turbulence, and due to this, no reverse draft will be created. That is why quite often a tab from a round ceramic pipe is built into a brick square chimney, which has an absolutely smooth surface and does not have internal corners.

Section size

In connection with the factors mentioned, it is necessary to carefully calculate the internal size of the chimney, while taking into account its length, since the larger this parameter, the higher the draft in the pipe.

Of great importance for the creation of normal traction and the high-quality functioning of the heating device is the correspondence of the parameters of the chimney passage and power, as well as the size and number of channels provided for by the design and passing inside the furnace.

If the parameters of the internal dimensions of the chimney in the cross section exceed the calculated value, this will lead to a rapid cooling of the heated air in it and the formation of condensate, and hence a decrease in thrust. In this case, the necessary balance will be violated, and the streams cooling in the upper part of the pipe may return down, creating smoke in the room.

The size of the chimney opening is calculated as follows:

The size of the chimney of an open hearth fireplace corresponds approximately to the proportions of 1:10 (chimney section (f) / firebox window area (F)). This formula is generally valid for both a square or rectangular, and a cylindrical type of pipe, but not directly, but taking into account the cross-sectional shape of the channel and the total height of the chimney.
The size of the chimney of a furnace with a closed combustion chamber has a proportion of 1:1.5. In the case when the heat transfer of the heating structure is less than 300 kcal / h, then the cross section usually has a size of 130 × 130 mm or half a brick (at least). When making calculations, it must be taken into account that the cross-sectional size of the chimney should not be less than the inlet of the blower.

When calculating the fireplace chimney, you can use the following table.

Pipe height H, m		5	6	7	8	9	10	11
		f/F ratio in %
Pipe section	Round	11.2	10.5	10	9.5	9.1	8.7	8.9
	square	12.4	11.6	11	10.5	10.1	9.7	9.4
	Rectangular	13.2	12.3	11.7	11.2	10.6	10.2	9.8

Pay attention to the direct dependence of the chimney cross-section not only on the parameters of the furnace, but also on the height of the pipe. Probably, sometimes in the calculations it will be more expedient to build on this parameter. For example, a pipe 11 meters high on a one-story country house will look absolutely ridiculous.

The same dependence, but more accurately represented in the form of a graph.

Suppose you need to calculate the cross section of the chimney for a fireplace with a firebox, the window dimensions of which are 500×700 mm, that is, the total area - 0.35 m². It is assumed that a pipe with a total height of 7 meters.