A chimney on the roof of a house, from which smoke is sure to come out, is a popular subject of children's drawings, even if the child grows up in urban areas and has never been to a real village. The kids are not yet aware, but adults know (or must know) that the chimney for the fireplace must comply with building codes ensure efficient and safe operation of the hearth. Alas, big uncles, "self-builders" and builders inexperienced in the profession often get into trouble, not paying due attention to this issue. In our article - short review the most common mistakes when installing a chimney and recommendations on how to avoid them.

Incorrectly selected chimney configuration

If it is difficult to kindle a fireplace, the flame burns sadly, and part of the smoke enters the room - the draft is weak, the reasons must be sought in an incorrectly selected chimney configuration. Moreover, the traction force is not constant, it can vary significantly depending on the direction and speed of the wind, other weather conditions. It should be mentioned that a prerequisite for having good traction (and a healthy microclimate in the house) is the presence of sufficient inflow fresh air from the street. The flame burns a large amount of oxygen, the chimney works like a powerful hood. Modern window systems practically sealed when closed. It is recommended to bring a separate air duct from the street to the fireplace with the possibility of adjustment. Or, during the firebox, set the window fittings to the micro-ventilation mode, open the window.

Insufficient chimney height

For good draft, it is necessary to ensure sufficient height of the chimney according to two parameters:

• Total height from the grate to the head chimney on the roof should be at least 5 meters. The higher the height, the stronger the thrust.
• The pipe should rise above the ridge by at least half a meter, provided that it is located at a distance of up to 1.5 m from it. If further, the mark is determined taking into account the angle of the roof.

Please note that the height of adjacent buildings must also be taken into account.

The chimney must not be combined under one hood with ventilation pipes. If they are located in the same block, the exit from the hearth should be raised higher.

Such a design is called a “candle” in construction slang. If the head of the chimney is not taken out of the common cap, in addition to weak draft, smoke may be thrown back into the premises

Significant deviation from the vertical

The straight vertical tube provides the best traction. Bends, inclined and even more so horizontal sections worsen it. If it is not possible to make the chimney straight, it is advisable to make the offset using inclined elements, and choose an angle of no more than 45º. The norms still allow you to arrange a horizontal section at the connection point, but its length is limited to one meter. The sum of horizontal projections of the displacements of the axes of the pipes from the level of the exit from the fireplace to the head on the roof, regardless of the slope of the pipes, should not exceed 2 m. In this case, the minimum height of the chimney (5 m) should be increased by this value (the sum of the projections).

The sum of horizontal projection offsets is calculated regardless of the direction in which the rotation occurs. For the case shown in the drawing on the right, the offset of the lower and upper marks of the pipe relative to the vertical will be A-B, but the value we are looking for is A + B

Wrong section defined

The cross section of the chimney for the fireplace should not be less than it should be, more - please, but in moderation. Define optimal parameters not difficult:

• For a factory fireplace, you just need to look at the instructions for a specific model. Such fireplaces have a round profile outlet with a diameter of 150 to 260 mm.
• The dimensions of the chimney for the fireplace can be roughly determined based on the size of the firebox. Roughly: the cross section of a round profile pipe should be equal to 10% of the area of ​​\u200b\u200bthe fireplace mirror (the width of the portal multiplied by its height). For more accurate calculations, the shape of the chimney (square, rectangle) and its height are taken into account. In addition to formulas, you can use graphs of the interdependence of indicators.

The graph on the left shows the amount of correction when determining the sections of square and rectangular chimneys in relation to round ones. The graph on the right determines the diameter of the chimney for a fireplace in relation to the area of ​​​​the portal, taking into account the height of the chimney

If the chimney is made of brick, it is also necessary to make allowance for the resistance to the movement of gases caused by uneven masonry. Depending on how carefully it is made, the cross section must be additionally increased by 5-20%.

How to improve draft without altering the chimney

Is it possible to improve draft without redoing the chimney inside the house? Yes, there are three ways:

• Increase the height of the chimney above the roof. This can have a positive effect in certain wind direction if the pipe is at a significant (more than 1.5 m) distance from the ridge.
• Install a special chimney weather vane on the head. In calm weather, it does not manifest itself in any way, but in windy weather it protects against blowing, prevents the occurrence of reverse thrust

It is necessary to monitor the operability of the rotary node of the weather vane, it must rotate freely

• Install an electric exhauster. This is a moderately expensive way, but guaranteed to be effective.

The electric smoke exhauster (roof fan) is designed to work with exhaust gases with temperatures up to 250 ºС, this corresponds to the normal combustion mode, but no more. It is necessary to remember this limitation and not overheat the firebox

Incorrectly selected pipe material and incorrect installation

The properties of the material for pipes must correspond to the operating conditions. For the manufacture of a chimney, the following materials can be used:

Brickwork

Traditional and reliable. It should be noted that the quality of roasting of a corpulent kiln brick should be high. This is especially important when connecting a long-burning factory firebox to the chimney. In economy mode, the temperature of the exhaust gases is low, because of this, condensate may form in the pipe. Insufficiently strong and porous brick will begin to collapse, most quickly above the roof, where moisture will freeze in winter.

Weakly burnt brick is not suitable for a chimney

The optimal solution is to mount an insert made of of stainless steel.

The steel liner can be lowered into a straight brick channel both during and after construction, this suitable option during the reconstruction of the building

The liner should not hang freely in the masonry. To do this, it is fastened with clamps, if mounted together with the construction of the pipe, or supplied with spring elements (as in the figure), if inserted after

Stainless steel pipes

Stainless steel pipes, single and double insulated - the most popular and affordable type of chimney today. Do not require the construction of a foundation, quickly installed. However, the mistake of some developers is to choose a product solely for the price without taking into account the properties of the metal. Not all types of steel are fully suitable for operation with fireplace inserts. Heat-resistant (working temperature 700 ºС and above) are grades AISI 304, AISI 309, AISI 316, AISI 321. Working temperatures of grades AISI 430, AISI 409 start from 500 ºС. Maximum temperatures, which steel can withstand for a short period of time, is higher by 200-250 ºС.

Exhaust gases in fireplaces with a closed firebox are heated up to 200-500 ºС, open - up to 350-600 ºС. However, these data are valid only until the hearth is heated in the normal mode, loading firewood no more than it should and not exceeding the intensive burning time specified in the instructions. Those who like to “fire up” the fireplace quickly and heat it up hotter may well bring the temperature of the exhaust gases at the chimney inlet to 1000 ºС. As you move along vertical chimney they noticeably cool down, but the first half-meter-meter can heat up very, very strongly.

Which pipe to choose for the chimney? The ideal solution is AISI 321 steel. At a relatively moderate price, it has sufficient heat resistance, is resistant to soot fire, and is acid-resistant. Pipes of this brand are best suited for gas fireplaces. For coal (there are some), it is advisable to use the AISI 309 brand, its heat resistance is higher, but the price is higher. If the budget is tight, the design of the chimney for the fireplace can be a compromise: the first segment from the firebox about a meter long is made of AISI 321 pipe 1 mm thick, less expensive steel is used above, for example, AISI 409, the thickness can be reduced to 0.8 mm if heat the fireplace moderately. It must be remembered that such a chimney may not withstand the ignition of soot and you need to monitor the cleanliness of the internal surfaces of the pipes, use high-quality fuel. The stainless steel grade for the outer sheath of the insulated pipe does not have of great importance, and a thickness of 0.5 mm is sufficient.

It is recommended to connect the insulated chimney to the furnace through an uninsulated section 40-100 cm long, this will prevent it from overheating.

The illustration shows a diagram of a chimney for a fireplace made of double insulated stainless steel pipe. Overheating of such a chimney is unlikely: an uninsulated adapter above the firebox relieves strong heat in the initial section, and the hot water tank located above serves as an additional cooler

Ceramic chimneys

They fully comply with the requirements for a fireplace, but are quite expensive, so they are used infrequently.

Modular ceramic chimneys are very reliable, but domestic enterprises are in no hurry to establish their production, and imported roads

Enamelled air ducts

A few words about enameled air ducts, which sellers often offer for fireplaces. Working temperature of such pipes does not exceed 500 ºС, the maximum - 650 ºС. Theoretically, they are suitable for closed furnaces, in which the instructions expressly allow the use of chimneys with a temperature limit of 500 ºС. In practice, if the manufacturer's recommendations are violated and used with powerful fireboxes, the enameled pipe may not withstand the increased thermal load. At best, the coating will melt, at worst, the steel will burn out.

Fire code violations

It will not be possible to describe all the intricacies of the fire prevention measures carried out during the laying of the chimney within the framework of a short chapter. More detailed materials are available on our resource, much can be gleaned from the instructions for the factory firebox. Let's mention the most important points:

• Between the chimney and combustible structures (ceilings, access to the roof) there should be a fireproof section filled with fireproof material, suitable for this purpose basalt wool. Distance from outer surface chimney and wooden structures is determined by the type of fireplace or stove and the type of pipe.

The chimney must be reliably isolated from combustible structures.

In any case, it must be at least 13 cm for sandwich pipes and 25 cm for single pipes. If the plates covering the hole are made of steel, wooden structures they are applied through a sheet of insulating material (asbestos cardboard, glass magnesite, GVL).

Fire separation must be present when passing through both horizontal and vertical structures

• A brick chimney instead of cutting with cotton can have a thickening of up to one and a half bricks (38 cm) with an asbestos cardboard or LSU gasket at the points of passage through combustible structures.
• Between the chimney and walls made of combustible materials, it is necessary to maintain a certain distance or install protective screen.
• It is important to correctly install the lining of the factory fireplace insert, eliminating its overheating. between the ceiling and inner space cladding should be a convection chamber, separated by heat-insulating screens. In cladding and chamber need to be done ventilation holes sufficient section.

The design of the chimney and fireplace, assembled taking into account fire safety requirements, should look something like this. The chimney must be reliably isolated from combustible structures

In conclusion, we note that the calculation of the chimney for the fireplace and its installation is a responsible matter and the performance of these works should be entrusted to qualified craftsmen.

Video: chimney for fireplaces

With all the diversity external forms and sizes of fireplaces, all of them are standardized products. The reason is that for the normal combustion of fuel and the removal of smoke, an air flow is necessary that can deliver the required amount of oxidizer (oxygen) and prevent the exit of combustion products from the furnace in any direction except the chimney. Compliance with all dimensions of the fireplace is the key to its reliable operation.

thrust

Air enters the furnace through the portal (window) of the fireplace. It is believed that in order to correct operation heater the speed of air movement through the portal must be at least 0.25 m/s.

In practice, it is difficult to measure the speed value. Before kindling the fireplace, one can only determine whether there is draft or not by the deflection of the flame of the lit paper. How good or bad the draft (air flow rate) is, the user of the fireplace is convinced in practice by the smell of burning (smoke in the room) and the speed of burning wood.

Traction is influenced by many parameters, among which are the temperature inside and outside the room, the degree of heating flue gases, the condition of the chimney (the presence or absence of cracks in it, through which additional air is sucked into the pipe), the type, quantity and humidity of the fuel.

But the most important condition for the correct operation of the fireplace, which ensures its functioning within a wide range of variable parameters, is compliance with the main dimensions and their ratios in the design of the heating device.

The main dimensions of the fireplace design include the height (B), width (A) of the fireplace window and its area (F), height (Htr), dimensions of the flow section, cross-sectional area of ​​​​the chimney (f). Of course, all these sizes can be different, but a certain ratio must be observed between them, otherwise the fireplace will not be able to work.

It does not determine the efficiency of the fireplace, but the depth of the firebox © and the dimensions that determine the position of its side walls significantly affect the efficiency of its operation. No less than the parameters of the firebox, the efficiency of the fireplace is affected by the size and position of the fireplace tooth (protrusion), the height of the beginning of the protrusion from the hearth of the fireplace (L), the excess of the tooth level above the upper border of the fireplace window (G), the width of the chimney opening not covered by the fireplace ledge (M).

The remaining dimensions of the fireplace do not affect its performance and efficiency. The shape of the fireplace, the dimensions of the body, the position of the fireplace table (mantelpiece) should be chosen based on how harmoniously the fireplace fits into general interior premises.

It was already mentioned in the article “Fireplace Device” that the area of ​​​​the window of the fireplace portal is chosen depending on the volume of the room in which it is installed, namely, the number square meters window area should be 20 times less than the number cubic meters room volume. Based on the selected dimensions of the fireplace window, the cross-sectional area of ​​​​the pipe is calculated not less than 1/16 of the portal area. If the fireplace is attached to an already finished chimney, then based on the required ratios, the calculation is based on the dimensions finished pipe, from which the allowable parameters of the fireplace window are calculated.

The above reasoning and relations are basically correct, but they do not take into account important parameters- the height of the chimney and the shape of its section.

The cross section of the chimney can be round, square or rectangular. Smoke (chimney gases) rises through the pipe not vertically upwards, but in ascending spiral streams. AT round pipe the shape of the flow corresponds to the shape of the pipe, all its space is occupied by a single upward flow of gases.

in pipes square section vortices are formed at the corners, directed against the main gas flow, as a result, the upward movement of smoke occurs not over the entire cross-sectional area of ​​​​the pipe, but only in its center, which practically leads to a decrease in the effective cross-section of the pipe. The turbulences that form in rectangular pipes interfere even more strongly with the upward movement.

Due to the decrease in the effective cross-section of the pipe, depending on the shape, round, square and rectangular pipes, having the same proportions in relation to the portal area, remove smoke from the fireplace with different efficiency.

An accurate engineering calculation of the parameters of a chimney is a task more for a theorist than for a practitioner, requiring not only taking into account many non-constant parameters, but also the possession of certain special knowledge in heat engineering.

In practice, they usually use averaged tables and diagrams calculated by specialists. Various specialized firms offer chimney calculations for own products, so the exact values ​​of the "proprietary" parameters may vary.

The figure shows a diagram developed by the German company Shiedel, which links the diameter of a round chimney of its own production with the height of the chimney and the area of ​​​​the portal of an open fireplace.

The following diagram makes it easier to choose the height of a chimney with different opening geometries depending on the ratio between the area of ​​the portal and the section of the chimney opening.

As can be seen from the graph, the difference in the height of the pipe required to provide thrust for the same values ​​of the ratio of the portal area and section is quite significant. In practice, the ratio is chosen depending on the diameter of the pipe available, and during the construction of brick pipes, they are guided by the dimensions of the opening lined with whole full-sized bricks.

Another factor influencing the final height of the chimney is the placement of the chimney outlet above the roof. When the pipe is located near the roof ridge (up to 1.5 m), the upper cut of the chimney should be located at least 50 cm above the ridge. At a distance of 1.5-3 m - it should not fall below the ridge. At a distance of more than 3 m, the angle between the horizontal line passing through the ridge and the line connecting it with the upper cut of the pipe cannot exceed 10 °. If we neglect the recommendations, then the draft will be significantly reduced by the air flow formed by the atmospheric wind blowing from the side of the opposite roof slope.

The values ​​of the pipe height and the relationship between the pipe section and the portal area given in the tables and diagrams are not absolute. The difference in figures obtained from different sources is explained by the fact that there are no clear boundaries between a fireplace that works correctly or with some minor flaws. In addition, as already noted, other factors, and not just geometric dimensions, also affect the efficiency of the fireplace. Therefore, to practically determine (especially before the start of operation) how ideally it will work heating device, impossible.

If there is any doubt about the appropriateness of a particular figure, the best adviser is personal experience. Unfortunately, House master usually does not have it, so you can not do without consulting a professional.

We thank the company for their help in preparing the material. The company "RETRO" carries out the whole range of furnace works, is engaged in the manufacture, repair, restoration of stoves and fireplaces.

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The construction of a chimney is an extremely important and responsible business, during which the likelihood of any errors and shortcomings should be minimized. Incorrect design inevitably entails significant losses of time and money for restructuring, which is simply impossible not to do, because this can lead not only to bad traction but also cause fire or carbon monoxide poisoning.

Chimney design highlights

At the design stage of the chimney, you should first determine the material from which it will be made. The choice of material, in turn, largely depends on what fuel this heater will operate on. For example, a brick chimney is ideal for wood-burning stoves and fireplaces, but it is strongly not recommended for use with gas boilers.

It is extremely important to correctly calculate the cross section of the chimney, its diameter and height. If you make a mistake when choosing one of these parameters, then this will inevitably affect the efficiency of the entire heating system, and even lead to more serious consequences.

Can a chimney be universal?

One of the most important points in the process of designing and building a chimney is the choice of material for it. Today there are a large number of companies on the market offering modern chimney systems, which, according to them, are suitable for operation in any conditions and with any heating equipment, regardless of what fuel it runs on. However, in reality, this is nothing more than a marketing ploy, since such universal systems simply cannot exist. Of course, individual chimney systems are able to function quite tolerably with various conditions and the use of different fuels, however, in this case, there can be no question of compliance with all norms and requirements.

How to choose the shape of the internal section of the chimney?

To determine the optimal shape of the chimney, you need to understand the principle of its operation. The fact is that its walls are heated unevenly, and therefore the smoke, rising up, twists along the central axis. Based on this, it is easy to assume that the most suitable form the chimney is cylindrical.

When using chimneys with a rectangular cross section, turbulence will inevitably occur, serving as an obstacle to normal draft, and sometimes even appears. At the same time, than more speed of the thrust itself, the stronger the turbulences are formed, and the worse the process of gas advancement proceeds. This nuance must be taken into account when calculating the chimney draft, since in principle rectangular shape permissible, but only for those heaters that do not require strong traction. Moreover, such chimneys have their own plus - they retain heat longer than cylindrical pipes, therefore, when correct device for traditional ovens and fireplaces rectangular chimneys are the best choice. At the same time, for modern heating boilers operating on the "stop-start" principle, it is advisable to install cylindrical pipes. When using such boilers, savings are achieved due to the faster heating of the system to the desired temperature, since after that they go into standby mode. And faster heating is ensured due to strong draft, which is possible just in case of using cylindrical chimneys.

Calculation of the inner diameter of the chimney

In order to correctly calculate the diameter of the chimney for a particular heater, you should first of all read the instructions of the manufacturers, if they are not there, then it is recommended to adhere to the following rules.

When determining the section of the chimney for a fireplace with an open-type firebox, it must be taken into account that the ratio of their diameters should be 1 to 10 if a cylindrical chimney is used. The diameter of the square chimney should be related to the diameter of the firebox in a ratio of 1 to 1.5. In this case, the diameter of the chimney cannot be less than the diameter of the blower. The level of heat transfer should also be taken into account: if it is 300 cal / h, then minimum diameter the chimney should be 140x140 millimeters. The successful functioning of the entire heating system largely depends on how correctly the section is chosen.

Chimney Height Calculation

Another important question to consider during the design process is how long should the chimney be? To answer it, several factors must be combined and analyzed.

As you know, warm air rises. At the same time, as long as it is in the pipe, it remains warm, and, therefore, continues to rise. As soon as it leaves the chimney, it immediately cools down and stops rising. Thus, the longer the time the smoke stays inside the pipe, the higher its temperature will be, and the greater its volume will rise up, thereby creating draft. It turns out that the volume of the chimney directly affects the amount of air rushing up and creating draft. The volume, in turn, depends on both the height and the dimensions of the internal section of the pipe.

Based on the foregoing, it turns out that if there is, say, a five-meter cylindrical chimney, it is enough to increase its inner diameter in order to improve traction. In reality, this is not so. Due to the increase in the inner diameter, the cooling of the flue gases in the pipe will occur much faster. This effect can be compared to pouring hot tea from a cup into a flat saucer.

The calculation of the diameter of the chimney and its height must be made in accordance with a number of rules, as well as taking into account specifications materials and the building itself. For a more accurate calculation of the height, you can use special programs that reduce the likelihood of error to a minimum. The chimney pipe must not be below the level of the ridge, as this will lead to the formation of turbulence.

Thus, the height of the chimney should be calculated on an individual basis, because in order to choose the optimal size, you will have to take into account a number of parameters, including the distance from the window to the chimney and from the chimney to the vertical axis of the ridge, the angle of inclination of the slope, the thickness of the roof, etc. . In this case, the height is determined without taking into account the protective chimney umbrella.

How to connect a collective chimney

Sometimes circumstances dictate the need to use one chimney for several heaters at the same time. In such cases, special attention must be paid correct calculation all settings (such as maximum length horizontal section of the chimney, its height, diameter, etc.). This calculation is made taking into account which heating devices are planned to be used in the system, their type and power, as well as the fuel on which they will operate.

Suppose a boiler will be connected to a single pipe from common system heating and a traditional fireplace. It is clear that these are fundamentally different heating devices, one of which works on natural gas, and the other - on firewood. Accordingly, the recommendations regarding the chimneys used with them are radically different (read: ""). Is it possible to combine in this case? Practice shows what is possible. Let's see how this happens.

As you know, the calculation of the diameter of the chimney for the fireplace is based on the fact that it should be a tenth of the diameter of the firebox. Naturally, this size for the boiler will be excessive. In this case, it is worth paying attention to the fact that, as a rule, people use the fireplace only from time to time, while the boiler works constantly during the cold season. In this regard, one might think that a smaller diameter should be made. However, such a move would be fundamentally wrong. In those moments when the boiler will work on its own, of course, there will be no problems, but you just need to melt the fireplace, and in the pipe, no matter what the length of the horizontal section of the chimney located in the attic, increased aerodynamic resistance will inevitably occur. As a result, the heaters will not work properly, and carbon monoxide will begin to seep into the room.

The solution to this, at first glance, insoluble problem is the use of a two-way chimney.

The main advantages of this type of chimneys include:

• the possibility of their use in conjunction with various heating devices, both individually and connected at the same time;
• ensuring the stable operation of each device;
• savings on construction and installation;
• space saving.

Possible schemes chimneys, look at the video:

During the installation process, it is necessary to observe all the conditions for ensuring the correct operation of each device, as well as strictly follow the previously made calculations, so that later you do not have to think about how to extend the chimney or increase its diameter. On device brick chimney it must be borne in mind that for its compatibility with the boiler, a sleeve must be made that protects the brick from the negative effects of condensate.

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How to make a chimney calculation - 4 important points to consider when installing a chimney

For heating private houses in the cold season, they are most often used, either conventional brick ovens and fireplaces, or domestic heating boilers in solid, liquid or gaseous fuel. An indispensable condition for the normal operation of such heaters is the free supply of a sufficient amount of fresh air to the flame combustion zone, and the rapid removal of spent fuel combustion products into the atmosphere. To ensure compliance with these conditions, before installing the stove chimney, it is very important to perform a competent calculation of the chimney with natural draft, since not only the efficiency of the heating devices, but also the safety of the residents of a private house will depend on this.

Due to what natural draft is formed in the furnace

Most heating and cooking stoves and boilers autonomous heating they are not equipped with a system of forced fresh air intake and removal of exhaust flue gases, therefore the process of fuel combustion in them directly depends on the presence of natural draft in the chimney pipe.

Theoretically, the method for calculating the chimney is quite simple. To make it clear to the reader where natural thrust comes from, then I will try to briefly explain the physics of thermal and gas-dynamic processes that occur in the furnace during fuel combustion.

1. The furnace chimney is always installed vertically (with the exception of certain horizontal or inclined sections). Its channel starts at the top of the firebox vault, and ends on the street, at some elevation above the roof of the house;

1. Hot flue gases in the fuel combustion zone have a very high temperature (up to 1000 ° C), therefore, according to the laws of physics, they quickly rush upwards;
2. Rising up the chimney at a speed of about two meters per second, the flue gases create an area of ​​​​low pressure in the furnace;
3. Due to the natural rarefaction in the furnace, fresh air is supplied through the blower and the grate into the flame burning zone;
4. Thus, it is easy to understand that for the formation of good natural traction, several conditions must be met at once:

• The chimney must be located strictly vertically. In addition, the ode should be of sufficient height and as straight as possible, without unnecessary bends and turns at an angle of more than 45 °.

• Internal section smoke channel must be calculated in such a way that it allows the entire volume of flue gases that are formed during the combustion of fuel to freely pass into the atmosphere;
• In order not to create significant aerodynamic resistance to the movement of smoke, the inner walls of the pipe should have the most even and smooth surface with a minimum number of transitions and joints;
• As you move along the pipe, the flue gases gradually cool down, which leads to an increase in their density, and a tendency to form. To prevent this from happening the chimney pipe must be well insulated.

A significant positive effect on the force of natural traction is exerted by the wind on the street. This is due to the fact that a continuous flow of air directed perpendicular to the axis of the chimney creates a reduced pressure in it. Therefore, in windy weather, good draft in the furnace is always observed.

Moment 1. The choice of material and design of the chimney

The normative and technical construction documentation does not stipulate any strict requirements for the arrangement of furnace chimneys, therefore, each homeowner makes a chimney at his discretion. At the same time, I must say that all types of chimneys differ from each other not only in design and outward signs, but also in terms of heat engineering, weight and gas-dynamic characteristics.

1. Chimney from brickwork characterized high strength and durability, well withstands prolonged exposure to high temperatures, but poorly resists the effects of aggressive smoke condensate. Thanks to the massive brick walls, it has a high heat capacity and satisfactory thermal insulation properties. As for the issue of water vapor condensation and gas dynamics of a brick chimney, not everything is so good here.

• Massive brick chimney has significant weight, therefore, its installation requires its own foundation, which, in turn, also requires separate calculations;

• Rectangular or square shape the cross section of the flue ducts, in combination with uneven and rough inner walls, create significant resistance to the movement of flue gases, therefore, the cross section of such chimneys should be selected with a small margin;
• Lack of additional thermal insulation can lead to condensation inside the chimney, therefore, its walls must be of sufficient thickness so that the temperature of the flue gases inside does not fall below the dew point.

1. Asbestos-cement and ceramic pipes are sold in ready-made, and are easily assembled with their own hands, so they are often used in the construction of private houses to connect gas or solid fuel boilers. Many homeowners are attracted by their not very low price, but I want to remind you that when installing a chimney from asbestos-cement pipes, the following points should be taken into account:

• Asbestos-cement pipes have high thermal conductivity and do not retain the heat of flue gases well., due to which condensation can form inside, which will quickly lead to the destruction of the walls;
• To prevent this from happening, when installing an asbestos-cement chimney, it is important to choose the right thermal insulation material, and calculate its thickness in such a way that the temperature of the flue gases at the outlet does not fall below 110 ° C;
• At temperatures above 350°C, asbestos cement can crack and break down, therefore, between the inlet pipe of the chimney and the outlet pipe of the boiler, I advise you to install a remote spacer from an insulated metal pipe;
• Its length should be calculated in such a way that the temperature of the flue gases at the inlet to asbestos-cement pipe did not exceed 300-350°C;
• Asbestos-cement pipe, in itself, has sufficient rigidity. Despite this, for better thermal insulation and protection against mechanical damage, I recommend installing such a chimney inside a protective jacket made of brickwork half a brick thick.

1. Metal sandwich pipes made of stainless steel, in my opinion, are the most good option home chimney, which is equally well suited as for a massive brick slab, and for modern compact heating boiler. They are recruited from separate sections, so they allow you to make an external or internal chimney of almost any configuration with your own hands.

• The inner sleeve made of heat-resistant stainless steel has a perfectly smooth surface and round shape cross-section, therefore creates a minimum aerodynamic resistance to the flow of flue gases. For this reason, the internal diameter of the flue duct must match minimum value design characteristics;

• Insulated metal sandwich pipe has good thermal insulation properties, and does not need additional insulation, therefore, heat engineering calculations, in this case, are not necessary;
• When installing and assembling the chimney, each section must be mounted in such a way that it is attached to inner wall or building facade at least two points. In this case, the distance between the mounting brackets should be no more than 1200 mm.

1. Prefabricated insulated ceramic chimneys have similar characteristics, and can also be used almost without restrictions, in combination with any type of stove, fireplace or domestic heating boiler.

• They are designed and manufactured in the factory, in compliance with all necessary heat engineering calculations and the requirements of fire safety rules;
• This makes it possible to mount them in the form in which they are, without thinking about your own additional calculations;
• Despite this, I want to remind you that such a sandwich made of expanded clay concrete blocks, mineral wool insulation and inserts from a ceramic pipe, the assembly can be heavy, so it is also necessary to calculate and manufacture a separate foundation for it.

1. Recently on the market building materials a relatively new type of polymer chimney began to appear, better known under the trade name "Furan Flex". It is a flexible reinforced sleeve that is installed in an existing smoke channel and then filled with high pressure hot steam. under pressure and high temperature the sleeve straightens and polymerizes, as a result of which it completely fills the lumen of the smoke channel, and strengthens the pipe walls from the inside.

• Installation of such a polymer insert requires the use of special equipment. and strict observance of technological regimes, therefore, it can be performed exclusively by qualified specialists;
• Based on this, in this case, I do not recommend hammering your head complex formulas, and entrust the performance of all calculations to the engineers of the contracting organization that will perform the installation.

The asbestos-cement pipe has a rough inner surface, which contributes to the rapid adherence of soot and soot. Over time, the growing layer of soot reduces the internal sectional area and increases the aerodynamic resistance of the smoke channel, so I do not recommend using such pipes for furnaces and boilers for solid and liquid fuels.

Moment 2. Calculation of the inner diameter of the chimney for solid fuel stoves and fireplaces

In order to perform a correct calculation of the chimney draft, it is first necessary to determine the required internal cross-sectional area. In this section, I will tell you how this is done, using the example of calculating the cross section of a chimney for heating stoves and solid fuel fireplaces.

1. First of all, it is necessary to determine what volume of flue gases will be produced when a certain type of fuel is burned in a furnace in one hour. Such a calculation is performed according to the following formula:

V gas \u003d V * V fuel * (1 + T / 273) / 3600, where

• V gas- the volume of flue gas that will pass through the pipe in one hour (m³ / hour);

• B- the maximum mass of fuel that burns within one hour in the furnace (kg);

• V fuel- coefficient of the volume of flue gases that are emitted during the combustion of a certain type of fuel (m³ / kg).

• This value is determined according to special tables, and its value is: for dry firewood and sod peat - 10 m³ / kg, for briquetted brown coal - 12 m³ / kg, and for hard coal and anthracite - 17 m³ / kg;

• T– flue gas temperature at the outlet of the pipe (°C). With a normally insulated chimney, its value can be from 110 to 160°C.

1. Having the obtained value of the total volume of gas passing through the pipe per unit time, it will not be difficult to calculate the required cross-sectional area of ​​​​the chimney channel. It is defined as the ratio of the received volume to the flue gas velocity, and is calculated using the following formula:

S smoke = V gas / W, where

• S smoke- cross-sectional area of ​​the smoke channel (m²);
• V gas- the volume of flue gases per unit of time, which we received in the previous formula (m³ / hour);
• W is the reduced velocity of the upward movement of the gas-smoke flow inside the pipe (m/s). Here I must say that this is a conditionally constant value, and its value is 2 m/s.

1. In order to understand what pipe diameter we need to make a chimney, based on the obtained value of the circle area, we need to determine its diameter. For this, the following formula is applied:

D = √ 4 * S smoke / π, where

• D- the inner diameter of the round chimney pipe (m);
• S smoke- the area of ​​​​the internal section of the chimney obtained in the previous calculations (m²)

To make it clear to the reader, I propose to consider a simple example of calculating a chimney for a stove, if it is known that during heating, 8 kg of dry firewood burns in it per hour, and the temperature of the flue gases at the exit is 140 ° C.

1. According to the first formula given, we determine the maximum amount of smoke that can be released in one hour of burning 8 kg of dry firewood: V gas = 8 * 10 * (1 + 140 / 273) / 3600 = 0.033 m³/hour;
2. According to the second formula, you need to calculate the required cross-sectional area of ​​​​the smoke channel: S smoke = 0.034 / 2 = 0.017 m²;
3. The last formula allows you to determine desired diameter pipe, based on the known area of ​​​​its cross section: D = √4 * 0.017 / 3.14 = 0.147 m;
4. Thus, we determined that for this furnace, a chimney with an inner diameter of at least 150 mm is required for the bath.

If during the calculations you get a non-integer number, then I advise you to round it up to an integer value, however, such rounding is allowed within reasonable limits, because in this case, very large diameter It doesn't mean very good.

Moment 3. Calculation of the chimney pipe for domestic boilers

In this article, I deliberately did not give separate calculations for factory-made household solid fuel and gas boilers, since any instruction for the use of boiler equipment already contains all the necessary technical information.

Knowing the passport thermal power your gas boiler, the diameter of the chimney is easy to choose, in accordance with pre-calculated parameters.

1. For small heating boilers with a maximum heat output of not more than 3.5 kW, pipes with an inner diameter of 140-150 mm will suffice;

1. For household boiler equipment of medium power (from 3.5 to 5 kW), chimneys with a diameter of 140 to 200 mm will be required;
2. If the power of the heating boiler is from 5 to 10 kW, then pipes with a diameter of 200 to 300 mm will need to be used for it.

If the gas boiler is equipped with a built-in turbine to create forced draft, then the diameter of the exhaust pipe can be much smaller than the above values. In such a case, the recommended pipe size should be specified in technical passport products.

Moment 4. Determining the height of the pipe and the location on the roof

The strength of natural draft largely depends on the height difference between the level of the grate of the firebox in the lower part of the furnace, and the wind deflector or the mouth of the smoke channel in the upper part of the chimney.

In order for the heated flue gases to use their energy as efficiently as possible to create natural draft, it is very important to correctly calculate the height of the chimney relative to the grate and relative to the roof ridge.

1. The relative height of the furnace chimney, from the level of the grate to the mouth of the chimney, must be at least 5000 mm;

1. On the residential buildings with operated flat roof, the mouth of the chimney must be located at least 500 mm higher than maximum height side parapet or roof railing;
2. On houses with a gable or hip sloping roof, the mouth of the chimney must be located no lower than 500 mm from the level of the roof ridge;
3. If on a sloping roof the chimney is located on one of the slopes, at a distance no further than 1500 mm from the roof ridge, then it must also rise 500 mm above the level of the ridge;

1. In the event that this distance is from 1500 to 3000 mm, the smoker's wind deflector can be located at the level of the roof ridge;
2. On gentle sloping roofs with a small angle of inclination of the slopes, the chimney can be located at a distance of more than 3000 mm from the ridge. In that case, his optimal height is calculated in accordance with the scheme presented in the figure below.

Incorrect choice of the height of the pipe or its location relative to the roof ridge, with an unfavorable wind direction, can cause the formation of reverse thrust. This phenomenon is very dangerous, since it can lead to the release of burning coals and poisonous carbon monoxide from the blower or firebox into the living space.

Conclusion

Summing up, I want to note that when choosing materials, dimensions and configuration of the chimney, first of all, one should proceed from the maximum heat output of the heater. At the same time, you also need to take into account your financial capabilities, and what types of fuel your stove or heating boiler is designed for.

You can learn more about all the described types of chimneys from the attached video in this article, and if you have any questions or comments, I suggest discussing them in the comment form.

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