Chimney calculation: how to calculate the necessary parameters. Calculation of the chimney cross-section How to calculate a chimney for a boiler
The main function that a boiler room chimney should perform is to remove flue gases from boilers into the atmosphere and disperse them in this space. She also has additional function: they must create a natural draft resulting from the difference between the temperature in the firebox and outside.
We will introduce you to the types of smoke channels, the classification of which is based on design features and pipe material. Here you will learn how to calculate geometric parameters for specific example. Our advice will help you decide on the type and size of the chimney.
In large boiler houses, natural draft cannot ensure complete combustion; here it is created forcibly with the help of smoke pumps. The combustion process and the release of its products into the atmosphere should cause as little harm as possible environment and don't call emergency situations as a result of the occurrence of pressure in the furnaces that exceeds the norm.
Thrust is a separate aerodynamic process in which combustion products move from a zone with an increased pressure level to a zone with a lower pressure level. In this regard, chimney draft is the most important parameter when calculating the entire heating system private house. If the calculation is incorrect, it occurs reverse thrust, in which combustion products are not removed, but enter the living space. What factors determine the level of traction? How to correctly calculate the parameter? In what ways can you increase cravings if there is insufficiency? Read on.
What is traction
Education process natural traction in a chimney can be described from the point of view of a science such as physics as follows:
- gases heated by the combustion of wood or their analogues in a stove (boiler) have a temperature of about 1000ºC;
- according to the laws of physics, heated air always rises;
- climbing up special pipe(at a speed of approximately 2 m/s) the gases create an area of low pressure;
- pressure stabilizes due to inflow fresh air, which enters the furnace (boiler) through special blowers, grates and other similar equipment.
Based on the physical processes of the formation of natural draft in a pipe, it is possible to determine a list of factors influencing its value. These include:
- chimney length. In accordance with current standards, the length of the chimney duct should not be less than 5 m. The optimal length can be determined based on the location of the chimney on the roof;
- the material from which it is made. To facilitate the passage of gases as much as possible, it is recommended to make the chimney from materials with a smooth surface. inner surface. And if this rule is not followed, then resort to periodic cleaning of the channel to remove soot and other deposits;
- presence/absence of insulation. If the smoke channel is not insulated from the outside, then when the gases cool, a large amount of condensate will form, which negatively affects the draft level;
Chimney insulation can only be done with non-combustible materials.
- pipe section. It depends on the correct diameter chimney and the level of traction depends.
The draft in the smoke exhaust duct is also determined by natural factors:
- temperature and humidity inside the living space;
- weather conditions (wind, precipitation, low temperature, etc.);
- number of residents;
- frequency of ventilation and so on.
How to check the presence/absence of traction? You can check the draft level in the pipe using a lit match, candle or paper.
Thrust calculation
So, draft calculation is the calculation of the chimney cross-section for gas boiler, fireplace, stove or other heating equipment. How to calculate the cross section? To do this you need to define:
- the volume of gas that will pass through the chimney in 1 hour;
- cross-sectional area of the chimney;
- section diameter.
Calculation of gas volume
To calculate the volume passing through smoke channel gas the following formula is used:
V = B x V1 x (1 + T/273) /3600 , Where
B – mass of fuel burned per 1 hour of operation of heating equipment;
V1 – correction factor, which depends on the type of fuel used for heating;
T – gas temperature determined at the exit from the chimney.
Indicators V1 and T can be obtained from the table available in GOST 2127 - 47.
Calculation of cross-sectional area
After determining the volume of gases passing through the smoke channel, you can calculate the cross-sectional size of the pipe:
S = V/W, Where
V – volume calculated earlier;
W is the speed of passage of gases through the smoke channel (this value is constant and equal to 2 m/s).
Diameter determination
The next step is to directly determine the diameter of the chimney. The following formula is used for this:
D = √4 * S/π, Where
S – cross-sectional area of the smoke exhaust channel;
π is a constant equal to 3.14.
Example
For example, let’s carry out the calculation using the specified formulas with the following parameters:
- 10 kg of wood is burned every hour in the stove installed in the bathhouse;
- the temperature of the gases at the outlet of the pipe is 130ºС.
Let's calculate the volume of gases:
V = 10x10x(1+130/273)/3600 = 0.041 (m³/hour)
Let's determine the cross-section of the smoke exhaust pipe:
S = 0.041/02 = 0.0205 (m²)
Let's find the most suitable pipe diameter according to the given parameters:
D = √ 4 * 0.0205 / 3.14 = 0.162 (m)
This means that for the stove used in the example, it is enough to install a chimney with a diameter of 165 - 170 mm.
How to make calculations and install a chimney yourself, watch the video.
How to increase traction in an already installed channel
The above calculations make it possible to build a chimney with optimal parameters to obtain a normal level of natural draft. What to do if there is backdraft? Is it possible to increase the indicator and how to increase traction on your own? There are several ways:
- cleaning the smoke exhaust duct. When soot and other types of deposits settle, the working diameter of the pipe decreases significantly, which leads to a decrease in traction. You can clean it:
- using a metal brush - brush. To do this, you need to tie the ruff to a strong rope and add a weight to the structure. Cleaning is done from the roof;
- special means such as a “Chimney Sweep” log;
Using special means You must strictly follow the instructions provided on the product packaging or special insert.
- folk remedies. For example, raw potato peels, aspen firewood, and so on;
- elimination of design defects made during the construction of the pipe (elimination of cracks, lengthening or shortening, elimination of unnecessary bends, insulation, and so on);
- installation additional equipment.
The following can be used as additional equipment to enhance traction:
- regulator The device is installed on the pipe and by opening/closing the damper allows you to adjust the traction force in ;
- deflector-amplifier. The increase in thrust occurs due to the redirection of air flows formed due to an increase in the diameter of the device;
- vane. The draft stabilizer, like the deflector, is installed at the end of the chimney and serves to enhance draft due to the streamlining of air flows. In addition, the weather vane helps stabilize the draft level during strong gusts of wind;
- rotary turbine. When exposed to wind, the device begins to rotate, creating an area around itself low pressure, which increases traction.
Unlike other devices, a rotary turbine performs its functions exclusively in the presence of wind. In addition, the device does not protect the chimney from clogging with leaves, small birds and other pollutants.
All additional devices require periodic maintenance: cleaning warm time year and clearing ice in winter. If cleaning is not carried out in a timely manner, the performance of the device will be reduced to a minimum and the required effect will not be achieved.
Calculation of a chimney for a building under construction wood stove one of the most important conditions for the normal and high-quality functioning and operation of the system. Therefore, it is very important during construction to adhere to accepted norms and rules as much as possible. Next, we’ll talk about what average parameters need to be taken into account and how to determine them yourself.
Why is a chimney calculation required?
In order for your furnace to function properly, it is important that the fume exhaust system is set up properly. Two main parameters play a huge role in this, which we will get to know below. They will determine what draft there will be and how effectively smoke will be removed from the stove. How to correctly calculate a chimney pipe will depend not only on the functioning of the system, but also on the safety of people living in the room. Therefore, pay attention to any subtleties, study the theory, so that later you can easily find out and determine how to independently calculate the chimney.
What parameters need to be calculated?
To calculate, you need to determine the following parameters:
- Length. First of all, you need to determine the maximum height of the building, how many meters to the ridge of the roof in the very place where the future pipe is supposed to exit. Because some of the most important characteristics future system. Take into account the fact that channels that are too high will simply “eat up” the draft; as a result, it will reach the heat source at a lower speed, which means your stove will burn much worse. In addition, chimneys that are too low in relation to the roof are also “scary”; more about this below.
- Chimney diameter (section). As for this parameter, it is necessary to take into account not so much the dimensions themselves as the original shape of the pipe itself. Do not forget important condition, if you want to get a high-quality chimney system that works according to all the rules, then the pipe must be cylindrical. That is, be sure to make the walls round so that soot and soot linger less in the channel. Thus, you push away the moment. As for the size (diameter), it must be selected based on the cross-section of the main outlet pipe of the furnace or boiler. It is not recommended to use pipes with a diameter larger or smaller than the pipe. High probability of depressurization.
How to calculate chimney parameters?
As described above, you need to know certain parameters. If the two main parameters are height and cross-section, then there is one more indicator that must be taken into account. These are the characteristics of the heating equipment itself.
There are several forms of calculation, divided into:
- Accurate.
- Approximate.
- Automatic.
By the first, we need to understand that it is necessary to take into account a lot of factors, including gas temperature indicators, separation speed, height and speed at which combustion of a particular fuel will occur. These values must be substituted into a special formula; a detailed calculation will be given at the end of the article.
As for the approximate calculation, the size of the combustion chamber is taken into account. For example, let’s take the classic size of a regular chamber in a furnace or boiler - these are dimensions within the range of 500 by 400 mm. The substitution system is used, that is, 1:10. Then for round channels, the diameter will be 180 - 190 mm.
The third type of calculation is the use of special calculation calculators. As a rule, they provide more accurate data, but you need to know more initial parameters. Roughly speaking, this is the same first method of counting, but it is performed using a computer.
Determining the height of the chimney
We already know that the performance of the system depends on this parameter. Therefore, keep in mind that according to SNiPs, the average height should be 5 meters, but not more than 7 meters. With a shorter length, natural traction will not be formed in sufficient quantities. When calculating, follow the described rules:
- From the base to the highest point is more than 5 meters.
- Exit to flat roof is marked by an elevation of the pipe head by 500 mm.
- When erected on pitched roof, three meters to the ridge, the chimney, when drawing a visual line, should be located at a 10 degree angle. The shorter the distance to the ridge, the correspondingly greater the degree.
The diagram shows the correct height of chimneys in relation to various types roofs.
Determination of the cross section of the smoke channel
In order not to use complex geometric calculations, we recommend that you pay attention to the recommendations of experts. So, the diameter of the chimney must meet the following criteria:
- If the power does not exceed 3.5 kW, then a diameter of 0.14 cm is sufficient.
- Power up to 5 kW is equal to a diameter of 0.20 cm.
- Power up to 7 kW, equal to a pipe cross-section of 0.27 - 0.30 cm.
How does the diameter of the chimney affect its height?
The diameter of the chimney pipe partly only affects the height. Roughly speaking, you will not be able to expand the cross-section in order, for example, to reduce the length of the channel - these values are not interrelated, as many believe. Therefore, you should not “be tricky” with the diameter, adjusting a certain height, which will be below 5 meters or above 7 meters. The level of traction will be the same throughout the entire length from 5 to 7 meters. But it's too much large diameter, can reduce thrust and form vortices, although at first glance this seems absurd.
Calculation of the optimal traction indicator
In addition to calculating the diameter of the chimney, you also need to know the draft force. To do this, you will need to find Bernoulli's law and substitute the external and internal temperature data, as well as the pressure level. For the final calculation, take into account total loss pressure in both zones. If the indicators are identical, then the traction is in the optimal range.
Example of furnace calculation
As promised, at the end we give an example self-calculation. So, you need to calculate the diameter of the chimney for a wood-burning stove using the following formula:
D = 4*Vr/3.14*2 = 0.166 m.
The values are selected based on standard sizes and indicators according to the table. Where:
D – Section.
Vr is the required volume of air for combustion.
4 is standard parameter traction.
I welcome my dear reader and bring to your attention an article on how to correctly calculate the chimney in your home.
The main component of comfort in the home is warmth. The owner of the house has to solve heating problems in a private home. For heating, which can be installed independently (except for gas), including chimneys.
To ensure complete drainage flue gases from the premises, good traction and prevent the traction from tipping over, it is necessary to comply with the requirements of regulatory documentation.
It is the chimney that ensures the safety of residents. An incorrectly designed chimney is unable to completely remove toxic combustion products (carbon dioxide and carbon monoxide, sulfur oxides), smoke and soot. There can even be a fire if hot smoke enters the room. Particularly dangerous is the overturning of the draft - turning the movement of smoke in the opposite direction.
Therefore, when installing a chimney, it is necessary to correctly calculate its parameters - they ensure the creation of ideal draft and complete removal harmful substances.
What parameters require calculation?
The main parameters of any vertical chimney are the length and internal (working) cross-section of the smoke exhaust duct. All the information below is equally true for heating appliances using any type of fuel, but the parameters of chimneys for gas boilers are calculated by specialists from a licensed design organization.
Length
The length of the chimney is determined by SP 7.13130.2013. Its length (or height) is measured from the head at the top of the pipe to the grate of the heating boiler. The standard provides for the minimum height of the chimney and the height of the head relative to the roof ridge.
It should be borne in mind that the height determined by calculations is nominal. In fact, the chimney of a modern boiler is located on the side, the boiler outlet is located in the upper part of the unit at a certain height relative to the bottom of the firebox. Therefore, the actual length of the vertical part of the chimney will be slightly less than the calculated data - the distance from the bottom of the firebox to the outlet pipe. This distance can be determined from the unit drawing or measured.
Don't think that extending the chimney is a good thing. The draft is based on the rise of hot exhaust gases, and if the length of the pipe is too long, the gases cool and the draft decreases. For the same reason, the chimney must be insulated. Even traditional red brick stove chimneys need insulation. The situation with draft is further aggravated by the fact that the exhaust gases from modern boilers with high efficiency have a low temperature.
With a moderately elongated chimney, the draft increases, and more heat escapes into the atmosphere. Too strong a current of gases will extinguish gas heating units. .
Installing a low chimney in a residential building is completely unacceptable - there is not enough vacuum in it, gases rise at a lower speed, which is why the draft decreases. It is allowed to install low chimneys separately standing furnaces eg in the garden barbecue, etc.).
Chimney diameter
The diameter of the chimney is no less important for creating draft. When installing modern heating units minimum diameter determined simply by the unit’s passport (and the diameter of the outlet pipe). In addition, the regulatory documents provide the minimum cross-sectional dimensions of chimneys corresponding to a unit of a certain power. These data are given in the unit passport.
If for some reason the internal cross-section of the chimney is chosen to be square, then its area should be no less than the circular structure.
When using an existing traditional stove, the chimney is left the same. When constructing a brick stove and chimney with your own hands, you must use the project (preferably not downloaded from the Internet!) and lay out the pipe in exact accordance with the drawing. The same applies to free-standing brick structures.
Calculation methods
Professionals use several methods for calculating chimney parameters. When installing large industrial pipes, designers are tasked with very complex calculations. They take into account:
- quantity and composition of flue gases;
- concentration of harmful substances in combustion products;
- pipe material;
- roughness of the internal surface of the hog;
- meteorological situation in the region.
Calculation large pipes often serves as a topic for thesis At the institute. Fortunately, the size of chimneys in a private house is smaller, and the power of heating units is also inferior to industrial facilities.
When designing small pipe For a private home, simpler, although quite accurate, calculations are used. The chimney parameters obtained as a result of calculations ensure complete evacuation of combustion products from the firebox and ensure the safety of residents. Such calculations allow you to avoid mistakes in choosing parameters and when installing the chimney, and to avoid subsequent reworking of structures. Such alterations in an already built and finished house are much more difficult than during the construction process.
When calculating the parameters of chimneys of a private house, exact and approximate (Swedish) calculation methods are used.
Exact method
For heating, ready-made heating or heating and cooking units are often installed industrial production with a certain chimney diameter. With sauna heaters or oil stoves for garages, ready-made sandwich chimneys of small diameter (100 mm) are usually also installed.
For more accurate calculations, it is necessary to know the characteristics of the fuel and the heating boiler, the rate of rise of flue gases, the amount of fuel burned, the shape of the chimney (sectional shape, number of bends). The calculations are quite complex and require the use of some special data, so let’s consider the calculation for a wood-burning heating unit (fireplace) - they are often made original, relying only on the experience of the stove maker, so calculation of the cross-section is necessary.
Let there be a chimney round section, no turns. Data for calculation:
- the average speed of movement of flue gases along the hog v is taken equal to 2 m/s;
- mass of firewood burned within an hour in the firebox – B=5 kg/h (humidity 25%);
- temperature of exhaust gases – t = 160°С.
Formula for determining the volume of exhaust gases:
where V is the volume of air required for complete combustion of 1 kg of fuel. For firewood with a humidity of 25%, combustion of 1 kg requires 10 m3 of air.
The value obtained as a result of calculations is rounded up to the nearest standard size round pipes(for example 125 mm). A square or rectangular brick chimney is not made smaller than 140x140 mm. The pipe cross-section for a traditional stove should be larger size blew one and a half times.
Volume of combustion products at normal conditions and the temperature of the outgoing smoke - standard data. See table:
Swedish calculation method
There is the so-called Swedish calculation method, based on the choice of the height of the chimney depending on the ratio of the furnace floor area and the cross-section of the pipe. Typically the method is used for wood-burning fireplaces. Calculate the ratio:
then the ratio is converted into a percentage and the height of the chimney is selected according to the graph, depending on the resulting size and shape of the hog.
Using Swedish method calculation, you can calculate the cross-sectional area of the bur channel based on the area of the firebox and the height of the pipe, determined in accordance with SP 7.13130.2013, depending on the height of the roof ridge and the location of the chimney relative to the ridge (see below).
How to correctly calculate chimney parameters
After the calculations, the height of the pipe is checked against the requirements of the regulatory document - it must be no lower than that required by SP 7.13130.2013. In any case, take a larger length.
The best chimney diameter is the one corresponding to the heating unit’s passport.
Determining the height of the chimney
The height of the chimney is determined at the design stage of the house, depending on the location of the pipe on the roof, the distance to the ridge or to neighboring tall objects (houses, large trees).
Why is this parameter needed?
The draft depends on the height of the chimney, which means the reliability and safety of the heating unit and the safety of the residents of the house. If flue gases are not removed sufficiently, the efficiency of the boiler, stove or fireplace decreases, and there is a danger of poisoning residents with carbon monoxide or carbon monoxide and the danger of fire.
SNiP requirements
In accordance with SP 7.13130.2013, the minimum height of the smoke exhaust pipe from the head to the grate of the heating unit must be at least 5 m. When the pipe exits to flat roof its height must be at least 0.5 m. Maximum length horizontal section should not exceed 1 m.
To create the required vacuum when the chimney exits the roof, the height of the pipe head above the roof is also specified (see table below).
There is also the concept of wind support. If the chimney is located near tall building, trees or a low free-standing chimney is located close to the house, then these objects can block the chimney from the wind and reduce draft. To determine whether the pipe does not fall into the wind pressure zone, it is necessary to draw an inclined line through the top point of the house or tree at an angle of 45° to the horizontal. The pipe head should be above this line.
Of the two height values, choose the larger one. If for compliance regulatory requirements If you have to build a very high chimney (much higher than 5 m), you will have to install a smoke exhauster that provides sufficient draft for any length of the pipe.
Table of the height of the chimney above the ridge
The height of the chimney above the ridge must comply with SP 7.13130.2013. The information is given in the table:
The distance from the ridge to the pipe is measured strictly horizontally.
Calculation of the cross section of the smoke channel
SP 7.13130.2013 determines the minimum cross-sections of the chimney duct of a brick or concrete chimney depending on the power of the heating unit:
- up to 3.5 kW – 140×140 mm (Ø no less than 158 mm);
- 3.5-5.2 kW – 140×200 mm (Ø no less than 189 mm);
- 5.2-7.0 kW – 140×270 mm (Ø no less than 219 mm).
When upgrading stoves with unknown power, either leave the existing chimney section or insert a round stainless steel liner inside suitable diameter. If to old stove install modern ceramic or sandwich pipes, the internal diameter of the modules must be no less than the diameter of the liner that would fit when installed in old pipe. Theoretically, you can look for a design for an old stove, but in most cases this is not possible.
Most often, a stove maker was invited, and he assembled stoves and chimneys of 2-3 mastered standard sizes without any designs or calculations. It is possible to determine all the features of a brick stove by appearance is impossible, and the only guideline when choosing the cross-section of a liner or a new chimney is the cross-section of the hog of a pre-existing chimney (provided that it worked well). If the chimney is, then when replacing or modernizing it, it is better to invite a heating engineer and entrust him with the appropriate calculations.
The diameter of pipes with an internal surface made of smooth ceramic or stainless steel may be slightly smaller (by 30%). The valves of solid fuel furnaces must have an unobstructed hole with a cross-section of at least 15×15 mm.
Internal section of the chimney: which is better?
In a square or rectangular chimney, there will be smoke turbulence in the corners, slightly inhibiting the flow of gases and facilitating the settling of condensation and soot. For the same reason, the corners of the pipe practically do not participate in the flow of gases. In addition, square and rectangular section larger area wall surfaces than those of round hogs - this increases the friction of rising gases against the walls and slows them down more.
Therefore, it is advisable to choose a chimney round shape, and modern pipes made of sandwich or ceramics are produced with a circular cross-section, just like pipes made of stainless steel and asbestos cement. The square or rectangular shape is found in older brick chimneys. But for modern boilers, stoves and fireplaces, a round stainless steel liner must be inserted into the brick box.
What to do if the chimney cross-section is square
But it is also possible to use a chimney square section– a square or rectangular shape does not have a very significant effect on traction, and a complete rework of the pipe is complex and expensive. Brick chimneys traditional ovens from time immemorial had a square or rectangular shape, if necessary, you can use the old pipe now.
It should be borne in mind that with a modern heating unit brick pipe Without a liner it will not work for a long time - it will be destroyed by chemically aggressive condensate.
The brick pipe should have a cross-section approximately one and a half times larger than that of a round chimney with smooth steel walls. Therefore, installing a liner does not impair the smoke removal ability of a square brick pipe.
What should be the diameter of the chimney for the stove?
Ideally, the diameter of the chimney should be equal to the diameter of the boiler outlet pipe or slightly larger (if the pipe has a non-standard cross-section).
The diameter of the chimney for the stove is determined from the cross-sectional area using the eternal school formula: s=πd2/4. The cross-sectional area should be equal to or slightly less than the cross-sectional area of a square hog, determined by regulatory documents depending on the boiler power.
How does the diameter of the chimney affect its height?
When installing a chimney, there is an immutable dependence: the narrower the cross-section of the hog, the higher the pipe should be. More tall pipe increases draft and rising speed of flue gases. But an excessively high one begins to slow down the draft - the hot gases cool down, and they are also slowed down by friction against the walls of the hog, especially a rough brick one.
Calculation of the optimal traction indicator
Draft – reduction of pressure in the chimney. Calculation of draft is needed to check whether the height and cross-section of the chimney hood are determined correctly.
where ∆P is the pressure difference at the inlet and outlet of the pipe, Pa;
a – Atmosphere pressure, Pa;
h – pipe height, m;
Ti – average indoor temperature, K;
To – external temperature, K.
For a non-specialist, the draft indicator does not provide sufficient information, so they usually calculate the volume of exhaust smoke, which is ensured by the presence of draft in the chimney. It is the volume of exhaust gases that shows how much the pipe ensures complete removal of exhaust gases with toxic substances and the safety of residents.
The formula is accurate only for air; for smoke the formula is approximate. But even by an approximate value it is possible to assess whether the chimney ensures the safety of people. The calculated value of the removed gases must be greater than or equal to the calculated value of the outgoing gases (see above).
where Vcalc is the flow of removed gases, m/s3;
S – cross-sectional area of the hog, m2;
C – coefficient taking into account friction losses; usually taken equal to 0.65-0.7;
g – free fall acceleration, 9.807 m/s2;
h – pipe height, m;
Ti – average indoor temperature, K (temperature in Kelvin is 273 units higher than the temperature in °C);
To – external temperature, K.
What causes natural draft in the furnace?
Natural draft in the chimney occurs due to the rise of hot and less dense smoke upward. A dense substance is sucked into the firebox from below cold air, oxygen reacts with the fuel, air and smoke heat up in the firebox, rise, and so on.
Calculation example
As an example, I will show the calculation of the volume of air removed for a pipe with internal diameter 0.125 m, area 0.012266 m2 and height e.g. 6 m, internal temperature 20 °C and minimum outside temperature-20 °C.
Conclusion: such a pipe ensures complete removal of flue gases from the firebox. Vcalc significantly exceeds Vout, so to reduce the cost of the chimney it is worth calculating Vcalc for a shorter or narrower pipe and consider the possibility of installing them.
When choosing a chimney of a smaller cross-section and height, it is necessary to calculate the draft at 10 °C - it will be less than at low temperatures, but Vout must be equal to or greater than Vcal even at positive temperatures, otherwise complete evacuation of carbon monoxide and carbon dioxide from indoors in warm weather.
In this case, Vcalc is significantly larger than Vout, since in the calculations we took a structure with a length of 6 m (and not the optimal 5 m) and rounded the calculated diameter of 0.118 m up.
Online calculators
Ready-made chimney parameters greatly facilitate calculations of chimney parameters. online calculators.
Conclusion
I say goodbye to my dear reader. When you build a new cottage or modernize an old house, pay special attention to the design of the chimney - this is the key to the safety of your family. Receive new articles from the site, bring friends to the site, share interesting and useful information with subscribers on social networks.
Before proceeding with the installation of the chimney, it is necessary to carry out design work, including calculation of the chimney and selection of the material from which the chimney will be made. On an industrial scale, it is more appropriate to entrust all calculations to professionals, but on a private construction scale, you can limit yourself to your own efforts.
Types of chimneys
Chimneys are designed to remove smoke and combustion products harmful to humans from a stove or other heating device outside the premises. In any chimney, the draft of the chimney formed during the process of filling the latter with gases must be produced naturally, that is, without the use of additional devices.
Currently, chimneys are manufactured:
- made of brick. For such a chimney, a solid foundation is additionally built. It is advisable to add lime to the composition of the connecting mixture used for bricklaying. This will avoid excessive accumulation of condensate, which can destroy the walls of the product;
- made of sandwich pipes made from two layers of metal, between which insulation is laid. In most cases, sandwich pipes are made using stainless steel, and basalt is used as insulation;
- from ceramics. Such chimneys are highly durable, but also very expensive. Therefore, they are used for arranging industrial chimneys. Due to the heavy weight ceramic chimney, just like a brick one, it requires the manufacture of an additional foundation;
- made of polymer. Such a chimney cannot be exposed to too high temperatures, so it can be used to remove harmful substances from geysers and small boiler houses. A polymer chimney is highly durable, low cost and easy to install.
In some cases, materials for the manufacture of chimneys can be combined. For example, a polymer chimney is lined with bricks.
The choice of material for making a chimney depends on the intended heating device.
Basic parameters for calculating a chimney
To calculate the dimensions of chimneys, consisting of the height of the chimney and the diameter cross section you need to know the basic parameters of the heating device used. You can find the required values in the accompanying documentation of the purchased equipment.
Calculation of chimney height
The height of the chimney affects the performance of heating devices. Minimum size chimney (according to fundamental documents - SNiP) is 5 m. If the chimney is less than the specified value, then the device will not generate the necessary natural draft. However, it is not recommended to make chimneys too high. In this case, the draft of the chimney is also reduced due to the slow passage and cooling of the smoke.
Calculation of chimney draft is used for the construction of industrial chimneys, and involves a very complex calculation system. For a private small building this figure is negligible.
In private homes, calculating the height of the chimney is based on the following rules:
- the total length of chimneys must be more than 5 m from the base to the final fungus;
- if the chimney goes onto a flat roof, then it should rise 500 mm above it;
- if on a pitched roof the chimney is brought out no further than 1.5 m from the roof ridge or if there is an additional fence on the roof, then the final pipe link should be brought out 500 mm beyond the level of the highest structure;
- if on a pitched roof the chimney is located within 1.5 - 3 m from the roof arch, then the height of the smoke exhaust pipe should be at the same level with it;
- if on a pitched roof the chimney is installed at a distance of more than 3 m from the roof ridge, then the height of the pipe should be calculated so that the horizontal level line of the roof ridge and the line connecting the roof ridge to the chimney form an angle approximately equal to 10º.
It should be noted that the chimney pipe should not be located close to skylights, doors and so on. This can cause sparks to enter the structure, especially in strong winds, and lead to a fire.
The height of the chimney located on the roof of the building is calculated in compliance with existing rules fire safety.
Calculation of the cross-section of the chimney pipe
- determine the amount of fuel burned in the heating device in 1 hour. In most cases, this parameter is indicated in the specification attached to the heating equipment upon purchase. An independent calculation of this indicator is presented below;
- temperature indicator of the gas located at the entrance to the chimney. The parameter can be found in additional characteristics equipment. In most cases, it is taken equal to 150ºС – 200ºС;
- the gas passage speed in the chimney is 2 m/s;
- chimney height;
- the natural draft indicator is assumed to be 4 Pa per 1 m of chimney.
Thus, the cross-section of the chimney depends solely on the amount of fuel burned during operation of the equipment.
When calculating the diameter of the chimney, you must use the formula for the area of a circle (where π is the number “pi”):
F=(π*d²)/4
Based on this formula, we get:
d²=4*F/π
To calculate the cross-sectional area of the pipe, it is necessary to determine the volume of gases located at the entrance to the chimney pipe. This parameter depends on the amount of fuel consumed and is calculated by the formula:
Vgas=B*Vfuel*(1+t/273)/3600, Where
- B – the amount of fuel in kilograms that is burned in 1 hour (kg/hour);
- Vfuel is a tabular coefficient depending on the type of fuel (you can find it in GOST No. 2127 or in the table below);
- t is the gas temperature recorded at the outlet of the pipe (also shown in the table).
The cross-sectional area (F) is found as the ratio of gas V to the speed of gas movement in the pipe (W), that is
F=Vgas/W
d²=(4*Vgas)/π*W
For example, heating a building for an hour requires 10 kg of firewood, the humidity of which is approximately 25%. The correction factor for this type of fuel, based on the above table, is equal to 10. The gas temperature recorded at the exit to the chimney pipe is assumed to be 150ºC.
Then the calculation of the boiler room chimney will be as follows:
- 1+150/273=1,55
- Vgas=10*10*1.55/3600=0.043
- d²=(4*0/043)/3.14*2=0.027
- d=0.165
That is, under certain conditions, the diameter of the chimney pipe must be at least 165 mm.
In order not to complicate the installation of a chimney with complex calculations, you can use the standards developed by specialists:
- for heating equipment whose power is less than 3.5 kW, a chimney with dimensions of at least 0.14 * 0.14 m is suitable;
- if the declared power of the heating boiler is within the range of 3.5 kW - 5 kW, then the parameters of the chimney must be at least 0.14 * 0.20 m;
- if appliances with a power from 5 kW to 7 kW are used to heat the room, then the cross-section of the chimney pipe used should not be less than 0.14 * 0.27 m.
If the power of the heating device is known during the construction of the chimney, then the data calculated by experts can be used to determine the cross-section of the pipe. If the power of the heating equipment is unknown, then it is necessary to carry out calculations according to the specified scheme.
Thus, when choosing a material for making a chimney, as well as when calculating the parameters necessary for its construction, one must rely on the power of the heating device. The greater its power, the larger and more reliable the chimney should be. If the parameters of the device are unknown, and it is not possible to calculate the required values on your own, then you must seek the help of qualified specialists. Any error in the calculations can lead to the chimney not working or to incomplete removal of harmful substances from the living space.
