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How to make a calculation chimney– 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 on solid, liquid or gaseous fuels. 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 for autonomous heating are not equipped with a system of forced fresh air intake and removal of exhaust flue gases, so 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 °.

• The internal section of the smoke channel must be designed 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 the minimum amount 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, so 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. The masonry chimney is characterized by high strength and durability, it can withstand long-term exposure to high temperatures, but it is poorly resistant to aggressive smoke condensate. Due 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;

• The rectangular or square cross-sectional shape of the flue ducts, combined with uneven and rough inner walls, create significant resistance to the movement of flue gases, so 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 ready-made and are easy to install with your 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 heat-insulating material and calculate its thickness so 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 the asbestos-cement pipe does 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. Stainless steel metal sandwich pipes, in my opinion, are the most successful option for a home chimney, which is equally well suited for both a massive brick slab and a 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 smoke channel must correspond to the minimum value of the 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 the inner wall or facade of the building at least in 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 a ceramic pipe insert, as an assembly, can have a lot of weight, so it is also necessary to calculate and make 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 hot steam under high pressure. 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 filling your head with complex formulas, and entrusting 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.

If the connecting elements are sheathed at least two centimeters thick with insulating materials that are not themselves combustible, only 10 centimeters is sufficient. In addition, it is prescribed that connecting elements are not located in walls, ceilings or cavities that are considered inaccessible. They are not allowed to enter other floors.

Chimney calculation

In order to achieve the best tensile properties in a chimney or furnace, they must be connected to an upper stack of chimneys. The thermal temperature is improved when the ascending flue gases pass through the vertically guided pipe section. It is also important that the chimney does not project into the cross section of the chimney, which is free.

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 lumpy 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 outlet 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 the desired pipe diameter, based on famous area 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, but such rounding is allowed within reasonable limits, because in this case, a very large diameter does not 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 nameplate thermal power of your gas boiler, it is easy to choose the diameter of the chimney, 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 forced draft turbine, the exhaust pipe diameter may be much smaller than the above values. In this case, the recommended pipe size must be indicated in the product data sheet.

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 residential buildings with an exploitable flat roof, the mouth of the chimney must be located at least 500 mm higher than the maximum height of the 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 not 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 gently sloping roofs with a small slope angle, the chimney can be located at a distance of more than 3000 mm from the ridge. In this case, its optimal height is calculated in accordance with the diagram 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.

It is not without reason that a house is compared with a living organism. All its components work in a tight "bundle". Violation of building regulations in the arrangement of the heating system inevitably entails difficulty in operation or even destruction of the roof structure. To avoid negative consequences you should know how the height of the chimney relative to the roof ridge is determined, how to find the optimal value.

Errors and inaccuracies in calculating the height of the chimney threaten serious problems. Due to unsuccessful calculations, the traction force will noticeably decrease. The stove is difficult, and sometimes impossible to ignite.

The more severe result of misses will turn into swirls in the chimney. The result of whirlwinds, the reverse movement of combustion products is smoke in the premises with all the ensuing threats and grave consequences.

The wind, colliding with the outer section of the chimney, changes the direction of its own movement. Simply put, having stumbled upon the wall of the pipe, the horizontal air flow tends to bypass it and turns up. "Change of course" forms a rarefaction of air in the area of ​​the attacked wall, due to which the smoke seems to be sucked out of the chimney outlet.

It is clear that for good draft in the chimney, the influence of wind is necessary. If insurmountable obstacles interfere with the horizontal movement of air flows, then the removal of flue gases will not be able to occur normally.

The ridge edge of a pitched roof can become such an obstacle if the dictate of the ratio of height and distance between it and the chimney is not observed.

Clear technological regulations

The rules for the optimal selection of the height of the chimney relative to the roof ridge are regulated by the collection of SNiP 2.04.05-91 in the subsection on stove heating. According to technical specifications:

• The total length of the smoke channel from the grate to the outlet must be at least 5 m. In houses with a non-attic roof structure, a chimney height of less than 5 m is allowed, provided that the draft is stable.
• The height of the chimney section above the flat roof structure must be at least 0.5 m.
• The chimney must rise above the ridge by 0.5 m or more if the horizontal distance between it and the ridge rib does not exceed 1.5 m.
• The mouth of the chimney should be flush with the ridge rib in height or slightly higher than it, if the horizontal distance between the pipe and the ridge line is in the range of 1.5 - 3.0 m.
• The outlet of the chimney must not be lower than the line drawn from the ridge towards the cornice overhang at a slope of 10º relative to the horizon.

The height of the ventilation and exhaust pipes is taken equal to the height of the pipe of the heating unit.

The most rational location of the chimney of pitched roofs is the maximum approach to the ridge rib, because:

• In any design option for a house with a pitched roof, location next to the ridge will provide the maximum distance from the bottom of the grate to the mouth of the chimney.
• The ridge barrier will not interfere with the impact of air currents on the chimney.
• The closest approach to the ridge guarantees the lowest costs for the construction of the smoke channel.

If there is no more than 1.5 m between the ridge rib and the pipe, then it is easy to cope with determining the height using the usual method of building a house model. To implement it, we will act as follows:

• On a house diagram made on a convenient scale, we draw a straight line parallel to the surface of the earth.
• From it, at the intersection of the roof with the chimney, we set aside half a meter upwards on the same scale.
• Draw a new horizontal line at the given point. It will indicate the minimum height at which the mouth of the chimney has the right to be.

Using a similar method, we find the height limit of the chimney if the horizontal distance between the ridge rib and the pipe is more than 1.5 m, but less than 3.0 m. Only we perform fewer actions. From the top of the roof, we simply set aside a horizontal line that will indicate the minimum height of the outer section of the smoke channel.

The most complicated process of calculating the height of the pipe above the ridge of a pitched roof is typical for situations where there are more than three meters between the chimney and the ridge rib. Then it is necessary to advance in determining the parameters of the chimney either mathematically or graphically.

It should be remembered that it is categorically not recommended to overestimate the size of the section of the chimney that extends beyond the roof structure. If the wind pressure is too strong, the high chimney can tip over. In situations where, for technical reasons, the formation of a high section of the pipe above the roof could not be avoided, its position is strengthened with stretch marks.

Graphic and mathematical technique

Let us analyze the most difficult option for determining the height of a chimney that is more than 3.0 m away from the ridge ridge. A vivid example of such design solutions is a house with large ones. The heating unit is usually installed so that it is possible to process all living quarters.

It often happens that a stove with a chimney located almost in the center of a complex structure crosses the roof structure in the extension area or close to the edge of the main slope, i.e. at a point far from the ridge. If the distance from the intended level of the grate to the planned outlet of the chimney is 5 meters or more, then its installation is possible.

• Graphic. According to him, the height of the outer section of the chimney is determined by geometric constructions.
• Mathematical. According to him, the size of the outer section of the pipe is determined using the known from school time trigonometric formulas.

The principle of graphic constructions is similar to the methods described above for obtaining the value of the maximum height of the chimney. In a scale convenient for work, a diagram of the house is drawn with precise dimensions and proportions.

A horizontal line is drawn at the top of the roof, from which an angle of 10º is laid down with the help of a protractor. The intersection of the proposed axis of symmetry of the chimney and the line drawn at a delayed angle will eventually give the desired value. The segment cut off by the lines should be measured and the height converted to a real value according to the scale instructions.

If necessary, the project of the house can be corrected by moving the axis of the chimney in a horizontal direction. Simple actions will help you find the optimal position of the channel.

Do not forget that between the roofing and the short side of the chimney there should be at least 0.5 m. And if the stove runs on solid fuel, then another 15 cm is added to half a meter to equip the otter or organize metal protection of the roof assembly from or metal tiles.

The mathematical method relies on the use of trigonometric formulas. Science learned in the classroom helps you quickly and accurately determine the minimum chimney height using just two known values.

Algorithm of mathematical calculations:

• We will measure the width of the house and its height in the ridge with a laser level, including the height of the walls and roof structure. In the absence of an expensive device, the width of the house can be measured with an ordinary tape measure. Do the same with the height of the wall and pediment, which will then need to be folded.
• Let's measure the distance between the central axis of the house and the central axis of the planned chimney.
• We draw a diagram of the house from the side of the pediment in a scale convenient for further work. The most acceptable scale for novice designers is 1:100. It means that in 1 cm of the drawing, a distance of 1 m of a real building will be displayed. The use of a convenient scale will prevent misses and errors when translating dimensions.
• We mark the central axis of the chimney on the drawing.
• Over the top of the house, she. skate, draw an auxiliary horizontal line. It and the central axis of the chimney must be extended to the intersection.
• With the help of a protractor, lay down 10º at the point indicating the ridge edge. We draw a line according to the received direction until it intersects with the central axis of the chimney.
• We got a right triangle, one of the legs of which will help determine the formula a = b × tgα.

In the formula: a - the value by which the pipe should be below the ridge ridge; b is the distance from the central axis of the house to the central axis of the chimney; α \u003d 80º (90º - 10º, the first value in the difference is the standard right angle, the second is the slope regulated by building rules, laid off from the horizon).

After intensive calculations, we obtain a value that must be subtracted from the total height of the house, measured along the ridge. Do not forget that the total height of the chimney from the grate to the outlet should be 5 m, and the minimum distance from the roofing to the mouth should be at least 0.5 m.

If, after taking measurements and converting the dimensions into a natural format, the scheme meets the construction requirements, then the option is successful and allows you to build a chimney at the planned location. If not, you will have to look for a suitable solution empirically by moving the central axis of the pipe closer to the ridge or in the opposite direction.

Rules and nuances of planning

Calculations and constructions alone are not enough to create an impeccable project. After all, the vertical channel of the chimney crosses the interior, which means it affects the layout.

With all the desire to install it closer to the ridge, it is not always possible to implement the plan. It often happens that you have to place at a considerable distance.

The following factors influence the location of the chimney inside the room and, as a result, the height of the outer section of the chimney:

• Internal layout of the equipped box.
• Chimney type.
• Number of floors.
• Ease of installation of the smoke channel.
• Providing access for maintenance.
• A type of material used in the construction of walls and roof structures.
• The number of units connected to one smoke channel.

Note that according to the rules for installing heating systems for private houses, a single unit must be connected to one chimney. Only in exceptional cases is it allowed to collect flue gases from two furnaces with one pipe. However, in such situations for correct operation the combustion products removal system is arranged inside the cut.

Furnaces of two-three-story houses are located one above the other. Their chimneys are built so that they exit through one shaft. Naturally, only the top floor stove pipe can be perfectly straight. All the rest are performed by withdrawals. The slip slope is 60º, its maximum length is allowed to be no more than 1 m.

By constructive type, chimneys are divided into:

• Wall. The most economical, convenient in construction and operation option, arranged in the main internal walls. They are used in brick and stone buildings - where it is possible to lay out a channel in a load-bearing wall.
• Indigenous. A variety constructed in the form of risers separate from the furnace. A more expensive design, but in some cases the only possible one. They are constructed if there are no technical prerequisites for the installation of a wall channel. They are mainly used in the construction of chimneys in stacks, folded with timber or logs.
• Attached. The type of chimneys is located directly on the ceiling - a reinforced concrete slab installed on the ceiling of the stove. They are used in small-sized buildings, dictating the need to save usable space.

The priority for designers is wall smoke channels - risers, because. their construction is carried out during the laying of the walls and allows you to save an impressive amount of building materials. True, it is impossible to arrange them in a box without an internal main wall. But if there are prerequisites for construction, the wall smoke channel will be as close as possible to the ridge run.

The wall chimney is laid using a buoy template, which is simply lined with bricks around the perimeter. This is a kind of wooden box with a section in plan, equivalent to the section of the smoke channel. Having reached the upper edge of the template during the masonry process, it is moved higher and overlaid again. So until the completion of the construction of the load-bearing wall.

Wall brick pipes are located mainly in the internal main walls. So the house is better heated, heating costs are reduced. There are situations when wall risers are laid out in the outer walls, but this solution is uneconomical and difficult to operate. When installing a chimney in an outer wall, its thickness increases.

Naturally, the construction of a pipe in the outer wall will force you to calculate the height of the chimney relative to the ridge using the methods described above. The height of the outer section of the chimney, built during the construction of the internal main wall, according to standard rules, is half a meter.

It is important to remember that smoke channels in walls made of foam concrete blocks or silicate bricks are laid out only from ordinary solid red bricks. This is subject to fire safety requirements. In the same standards, the distances between chimneys and combustible structures are indicated.

Retreat from an unprotected wooden ridge run and rafter legs should be 0.5 m, from protected analogues by 0.38 m. metal pipes should be removed from combustible structures at a distance of 0.7 m or more. Fire regulations must be observed when determining the distance between the chimney and the wooden components of the truss system.

There are no such strict rules in the design of root and cased pipes. Their location is more focused on architectural and planning specifics, ease of installation and future maintenance. The location of the chimney relative to the ridge can be whatever the owner of the house likes best, but taking into account the requirements of firefighters.

The part of the chimney that rises above the roofing should be plastered with a cement composition. The thickness of the plaster layer should be 2-3 cm. Within the attic space, the chimney must be whitewashed so that you can quickly determine the place of gas leakage and repair the dangerous area.

Video about the principle of the mathematical method

The video will clearly demonstrate the logic and process of determining the height of a chimney that is more than 3 m away from the ridge ridge:

Compliance with technological rules and building codes is a guarantee of the normal operation of the chimney and the long service life of the building structure.