Calculation of a chimney for a wood-burning stove: dimensions, diameter, height above the roof. Calculation of the cross section of the chimney Calculation of the diameter of the steel chimney of the boiler room

The stove or fireplace is called the "heart of the house" for a reason. But taming fire inside a residential building involves a number of actions and a long set of rules. After all, any mistakes in the design of the chimney are too expensive, starting with suffocating smoke indoors and ending with a fire. And most often it all starts with a violation of traction and the destruction of the walls of the chimney, and then the adjacent building structures ignite.

Today performing height calculations chimney often produced through special programs, although experienced specialists must check the obtained values by hand, using formulas that it makes sense to get acquainted with for the sake of peace of mind.

They are not difficult, for their understanding it is enough to have school knowledge of geometry and the ability to substitute values in the right place. And we, in turn, will try to explain to you why each indicator is so important for determining the height of the chimney, and how exactly it affects it.

According to all building codes and regulations, the chimney must rise above the roof at a certain distance. This is necessary so that the air on the protruding parts of the roof does not cause back draft due to turbulence.

The reverse draft can be seen with one's own eyes in the form of smoke that pours from the fireplace directly into the room. But the extra height of the chimney is also not needed, otherwise the draft will become too strong and you won’t wait for heat from such a fireplace: the firewood will be incinerated like a match, not having time to give heat.

If the pipe is located too close to dense trees or a high wall, it must be built up with asbestos-cement or steel pipe.

In this video you will also find valuable tips on chimney construction and solutions to problems with its height:

Traction force: how to achieve perfect combustion of fuel

The traction force itself is influenced by several important factors at once:

chimney material;
foundation height above sea level;
temperature flue gases at the exit from the furnace;
the form cross section chimney pipe;
smoothness or roughness of the inner surface;
violation of the internal tightness of the chimney;
temperature and humidity of the outside air;
ventilation of the room with a boiler or stove;
completeness of fuel combustion;
the degree of contamination of the boiler (or furnace) and chimney;
type of burner used (modulating or discrete).

First of all, you need to determine the value of the static draft of the chimney, and it is measured in the value of ∆p [Pa]. Here is the formula to calculate:

h[m]=(∆p Tp Tn)/(3459 (Tp-1.1 Tn))

Tr is the average temperature in the pipe, and Tn- outdoor temperature. It is measured by default in degrees Kelvin, but you can specify it in Celsius by adding +273.

Calculating the average temperature is not difficult. It is usually given in the technical data for the boiler, but it is also important to consider cooling. This is 1 degree per meter of brick pipe, 2 degrees per meter of insulated steel pipe, and 5 degrees for uninsulated pipe.

At the same time, it is advisable to take the value of the outside temperature that is typical for summer as the most problematic time for traction:

Make an aerodynamic calculation and find out the exact required height and diameter of the chimney. By itself, the thrust value means the difference in the density of air and flue gas, multiplied by the height of the house. It is 5 meters of the chimney that provide vacuum and draft for smoke.

But what to do if the height of the pipe cannot be set higher, and the thrust is still insufficient for certain reasons? This often happens when flue gases cool down too quickly, especially during the cold season. Then, to restore traction, the desired section of the pipe is simply insulated.

Also remember that the real thrust is always less than the static one due to the resistance of the movement of gases inside the pipe walls. The narrower the flow area of the chimney, and the more bends, horizontal sections and the like in it, the worse the draft will be, because the pressure loss along the entire length of the pipe affects the draft.

Another issue with chimney height is cold air from the fireplace. So, when it is not working, cold air is let out of it from the street. This happens when the chimney head is below the end of the ventilation hood, or when the attic is too large and poorly insulated.

Chimney design depending on the heating configuration

And first of all, when designing a chimney, its minimum throughput indicators are calculated. If mistakes are made here, flue gases will accumulate inside the pipe and cause many problems.

The general layout of the chimney looks like this:

If the flue gas temperature is low, as in modern low-temperature boilers, then so-called electric smoke exhausters are installed in the upper part of the chimney.

They are a small fan with blades. Such a device forcibly removes combustion products from the pipe, thereby increasing the traction force. And then the traction force no longer directly affects the height of the chimney, because it is achieved in a different way, and not by “catching the wind”.

If a accessory no, then you still have to catch the wind. And in this case, you need to build on the available power of the boiler, stove or fireplace, which can be found in the technical documentation. It is expressed in the amount of fuel that is burned in one hour of work.

If the amount of fuel volume is known, then the volume of gases is calculated using the following formula:

Vg = B∙V∙(1+t/273)/3600

The result will be in m 3 / s. This is the speed of movement of gases in the pipe. We calculate the pipe cross section using the following formula:

F = π∙d²/4

And the resulting value is determined in m 2. This is the cross-sectional area of the chimney, and the diameter is calculated by the formula:

dт = √4∙B∙V∙(1+t/273)/π∙ω∙3600

The rest of the characteristics are almost the same for most heating appliances. So, the speed of the exit of gases in the chimney is usually not less than 2 meters per second, and the temperature of the gases at the inlet to the pipes is from 150 to 200 degrees.

Also, the standard gas pressure per 1 meter is not less than 0.4 mm H 2 O, or 4 Pa:

Therefore, according to SNiP, the height of the chimney from the grate must be at least 5 meters.

Roof Flammability: When a Spark Leads to Trouble

It also matters roofing material, namely, its combustibility. So, with a fireproof coating, the height of the pipe should be increased by 1-1.5 meters so that sparks do not reach the roof:

The dependence of the height of the chimney on other elements of the roof

Of great importance is also how close the chimney itself is located to the ridge of the roof, the parapet or its other elements:

So, with regard to the elevation of chimneys above the roof, there are such rules:

Not less than 1.2 meters above a flat roof.
Not less than 50 cm above the roof ridge if the pipe is located up to 1.5 meters from the ridge.
Not lower than the level of the ridge, if the pipe is located from 1.5 to 3 m from the ridge.
Not below the line that can be drawn from the ridge down to the horizon at an angle of 10 degrees if the pipe is located more than 3 meters from the ridge.

In this case, the smoke channel must be located at a certain distance from other elements of the structure, at least:

150 mm for pipes with insulation;
500 mm for pipes without insulation.

The minimum allowed height of the pipe is 50 cm. But these are too low pipes, which are only allowed to be placed on flat roofs without any protrusions. If the roof is with a more complex configuration, you will have to tinker and take into account all the protruding parts.

So, if all these parts are at a distance of 1.5 meters from the pipe itself, then it is enough for the pipe to be simply higher than all these elements. If they are closer than 1.5 meters, then the chimney must exceed their height by at least 59 cm:

It is not difficult to maintain a chimney height of 5 meters from the fire grate to the upper cut of the pipe if a one- or two-story house was built. But problems arise if the fireplace was installed on the upper attic floor - the height of the ceiling and attic is insufficient here.

Environmental issues for industrial buildings

In a word, the throughput of the chimney must ensure the unimpeded passage of smoke and its release into the atmosphere. Moreover, the ecological moment is also important here, namely, whether the products of fuel combustion are dispersed in the atmosphere correctly.

So, in the construction of commercial and factory enterprises, certain sanitary norms. And they depend on the weather conditions of the area, the typical speed of the flow of air masses, the relief of the landscape and many other factors.

So, what value did you get and is it exactly 5 meters?

At independent device of the smoke exhaust structure, it is necessary to accurately calculate the parameters of the cross-section of the chimney, its overall height and the level of air circulation - draft, which will support the combustion process of the fuel and remove toxic combustion products contained in the smoke into the atmosphere. Such calculations are quite complicated, but important for ensuring the efficient and uninterrupted operation of the thermal unit and the safety of residents.

For the normal functioning of heating appliances that generate heat by burning fuel, a chimney is required.

The smoke-removing design provides an influx of oxygen, without which neither gas nor solid or liquid fuel burns. In addition, smoke containing combustion products is removed through the chimney, which is the key to the safety of the heating system - after all, smoke in the premises is deadly for humans. This gas exchange is called thrust.

Internal combustion boilers are equipped with coaxial chimneys, which create draft forcibly, removing smoke through one pipe and sucking it through another Fresh air. Wood stoves and most domestic boilers run on natural draft, which is formed due to the difference in temperature and pressure in the heating device and at the chimney outlet.

The principle of operation of the chimney is simple:

gases released during the combustion of fuel high temperature, low density and high pressure and it becomes crowded inside the heater;
smoke goes where there are no obstacles for it, that is, it moves in the direction where the pressure is lower, trying to fill the relatively free space, in addition, due to the low density, gases tend upwards;
if the chimney is arranged correctly, then the cold air at the outlet of the pipe has low pressure and is not an obstacle to the exit of hot smoke;
since as an area low pressure located above the boiler, then the smoke goes along the most convenient path - up the chimney to the street.

What are calculations for?

Natural air exchange, in which combustion products are removed into the atmosphere, occurs only if the smoke exhaust structure has correct form and size.

If there are obstacles - turns, corners, sections of the smoke channel with low throughput - the smoke can go in another direction, where nothing will interfere with its spread. With a small pipe height, the temperature difference will not be sufficient to form a thrust, or a wind backwater will appear, which will prevent the smoke from leaving the pipe, practically driving it back.

Note! Defects in the device of the chimney will lead to the fact that the draft will either be insufficient for normal operation heater, or will appear reverse thrust and fuel combustion products will enter the premises, which may cause poisoning or fire.

However, it cannot be said about the dimensions of the chimney that the larger the better. Too long or too wide a chimney will increase the cost of building a chimney. A furnace or boiler with such a chimney will work for wear in conditions of excessive draft, burning fuel faster than it is necessary to warm up the premises. The heat received during combustion will partially fly away into the pipe, which will increase heating costs.

Therefore, in order for the thermal unit to work efficiently and not break down, it is important to accurately calculate the main parameters of the chimney, which will ensure optimal level traction.

How to calculate the parameters for the chimney

For the construction of a smoke exhaust structure, it is imperative to carry out calculations:

overall height and height relative to the roof,
internal diameter of the chimney,
generated traction.

All these parameters are interconnected. The geometric dimensions of the chimney must be calculated to draw up its project, and the amount of thrust - to determine the operability of the chimney in normal weather conditions for the area.

Calculation of inner diameter

The main regulatory requirement for the size of the chimney pipe is its compliance with the outlet pipe thermal device.

Note! For factory-made heat generating units, it is enough to choose a pipe that has the same cross section as that of the outlet pipe, or a slightly larger size. Fulfillment of this condition will provide the necessary throughput chimney.

For wood stove or a domestic boiler that does not have a factory outlet, it is necessary to calculate the parameters of the internal section of the chimney, in which the chimney will have the necessary throughput.

To calculate the diameter of a round pipe or the width and length of a rectangular one, you need to find the area of its internal section. The calculation is carried out in several stages.

First, the volumetric output of flue gases per unit time (Vg) is calculated:

Vg=Mt*Vt*(tg+273)÷273,

where Mt is the fuel consumption per unit of time specified in the accompanying documentation of the heater,
Vt is the smoke emission coefficient of the fuel used,
and tg is the flue gas temperature at the chimney inlet, usually indicated in the documentation for the heater and equal to 120-150ºС.

The smoke emission coefficient varies for different fuels:

To calculate the cross-sectional area (S), it is enough to divide the obtained value (Vg) by the smoke removal rate (v):

S=Vg÷v.

The optimal speed is considered to be 1-2 m / s. At this speed, soot and condensate do not have time to settle on the pipe walls, but the heat remains in the room, and is not drawn out into the street.

Note! For accurate calculations, it is important to reduce all quantities to a single time parameter. If the speed for the calculation is used in m / s, then the fuel consumption must be converted to kg / s.

For example, if the standard flow rate for a wood-burning stove is 8 kg/h, then when converting, this value must be divided by 3600. Thus, the flow rate will be 0.0022 kg/s.

For a round pipe, the diameter (D) is calculated from the formula for the area of a circle:

D=2√S÷3.14.

For a square, the width (a) is calculated from the formula for the area of a square:

a≥√S.

For rectangular section the width (a) and length (b) are selected so that their product is greater than or equal to S:

S≥a*b.

Determining the height of the chimney

In order to create a sufficient difference in pressure and temperature in the boiler and outside, the minimum required height of the chimney pipe must be 5 meters. But apart from minimum value it is necessary to calculate the height of the outlet above the roof.

These calculations take into account the type of roof, the location of the chimney in relation to the roof ridge and the presence of closely spaced buildings or other tall objects.

Note! When designing a chimney, it is necessary to take into account the location of the fasteners. Every 2 m of height, the pipe is fixed to the walls and ceilings, if the chimney rises more than 1.2 m above the roof, extensions are used for additional fixation.

Thrust calculation

To check the operability of the chimney, which will be erected in accordance with the calculations made for the height and internal section of the pipe, an additional draft calculation is carried out.

Draft, that is, the pressure difference at the inlet and outlet of the chimney (P) is calculated by the formula:

ΔP=hd*(ρv-ρg),

where hd is the height of the chimney above the heater,

c - air density in the street,

d is the smoke density.

The height of the chimney has already been calculated, but the density of air and flue gases will need to be calculated. Depending on weather conditions, the air density indicator changes.

ρin=ρin*273÷tin,

where n=1.29 kg/cu.m. is the air density under normal conditions,

and tv is the ambient temperature.

It is important! To calculate thrust, the most unfavorable climatic conditions the region has a warm season. For calculations, the temperature in Kelvin is used, so we add 273 to the temperature in degrees Celsius.

Flue gas density is calculated using a similar formula, based on the average flue gas temperature in the pipe (tg):

ρg=ρn*273÷tg.

Δtg=(tg+td),

where tg is the temperature of the gases at the outlet of the heater, indicated in the accompanying documentation,

and td is the temperature of the smoke at the exit from the pipe.

But the temperature of the flue gases emitted by the chimney into the atmosphere requires additional calculations and depends on the power of the thermal device (Q) and the height of the chimney (hd):

td=tg-hd*V*√1000÷Q,

where B is the heat transfer coefficient of the chimney, depending on the material from which the chimney is made and the level of its thermal insulation.

If, after carrying out all the calculations, the thrust level turned out to be in the range of 10-20 Pa, then the designed chimney will cope with its task and ensure uninterrupted operation of the thermal unit. Otherwise, it will be necessary to increase the height of the chimney or equip the head with a deflector or a smoke exhauster to create artificial draft.

Note! Thrust calculations require accuracy, so all intermediate calculations must be recorded so that they can be verified. In order to exclude possible error in calculations, you can use an online calculator or contact a specialist.

Features of calculating the parameters of the chimney for domestic boilers

Factory-made thermal appliances usually do not require serious chimney calculations - the main parameters are indicated in the accompanying documentation. A distinctive feature of the calculations for household boilers is their simplicity.

Height is determined by general rules, taking into account the peculiarities of the location of the smoke exhaust structure relative to the roof of the house and nearby buildings.
The diameter of the internal section of the chimney is chosen in accordance with the power of the heat generating unit, without taking into account either the type of fuel or the volume of gases emitted. Since factory devices are produced according to manufacturing standards, all parameters have long been calculated and collected in a table.

Before proceeding with the installation of the chimney, it is necessary to carry out design work, including the calculation of the chimney and the selection of the material from which the chimney will be made. AT industrial scale it is more expedient to entrust all calculations to professionals, and on the scale of private construction, you can limit yourself to it.

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 filling of the latter with gases must be produced naturally, that is, without the use of additional devices.

Currently, chimneys are manufactured:

from brick. For such a chimney, a solid foundation is additionally constructed. It is desirable to add lime to the composition of the connecting mixture used for laying bricks. This will avoid excessive accumulation of condensate that can destroy the walls of the product;

from sandwich pipes made from two layers of metal, between which a heater is laid. In most cases, stainless steel is used for the manufacture of sandwich pipes, and basalt is used as a heater;

from ceramics. Such chimneys are characterized by high strength, but also high cost. Therefore, they are used for the arrangement of industrial chimneys. Due to the heavy weight ceramic chimney, as well as brick requires the manufacture of an additional foundation;

from a polymer. Such a chimney cannot be exposed to too high temperatures, therefore it can be used to remove harmful substances from gas water heaters and small boiler rooms. The polymer chimney is characterized by high strength at low cost and ease of installation.

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 the manufacture of the chimney depends on the proposed heater.

The main parameters for calculating the chimney

To calculate the dimensions of the chimneys, consisting of the height of the chimney and the diameter of the cross section, you need to know the main parameters of the heater used. You can find the required values in the accompanying documentation of the purchased equipment.

Chimney Height Calculation

The height of the chimney affects the performance of heating appliances. The minimum size of the chimney (according to the fundamental documents - SNiPam) is 5 m. If the chimney is less than the specified value, then the device will not generate the necessary natural draft. However, too high altitude chimneys are not recommended. In this case, the chimney draft is also reduced due to the slow passage and cooling of the smoke.

The calculation of the chimney draft is used for the construction of industrial chimneys, and it implies the most complex system of calculations. For a private small building, this figure is negligible.

In private houses, the calculation of the height of the chimney is based on the following rules:

the total length of the chimneys must be more than 5 m from the base to the end fungus;
if the chimney goes to flat roof, then it should rise above it by 500 mm;

if on 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 must 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 vault, then the height of the chimney should be on the same level with it;
if on a pitched roof the chimney is led to a distance of more than 3 m from the roof ridge, then the height of the pipe must be calculated in such a way that the horizontal line of the roof ridge level and the line connecting the roof ridge with the chimney form an angle of approximately 10º.

It should be noted that the chimney should not be located near skylights, doors and so on. This may cause sparks to enter the structure, especially when strong wind and lead to fire.

The height of the chimney located on the roof of the building is calculated in compliance with existing fire safety rules.

Calculation of the section of the chimney pipe

determine the amount of fuel burned in the heater in 1 hour. In most cases, this parameter is indicated in the characteristics attached to the heating equipment upon purchase. An independent calculation of this indicator is presented below;
temperature indicator of the gas located at the inlet to the chimney. The setting can be found in additional feature equipment. In most cases, it is taken equal to 150ºС - 200ºС;
the speed of gas passage in the chimney is 2m/s;
chimney height;
the natural draft index is assumed to be 4 Pa per 1 m of the chimney.

Thus, the section of the chimney depends solely on the amount of fuel burned during the 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 \u200b\u200bthe pipe, it is necessary to determine the volume of gases located at the inlet to the chimney. 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 of time (kg / hour);
Vfuel - 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 given in the table).

The cross-sectional area (F) is found as the ratio V of the gas to the velocity of gases 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 moisture content of which is approximately 25%. The correction factor for this type of fuel, based on the above table, is 10. The gas temperature recorded at the exit to the chimney is assumed to be 150ºС.

Then the calculation of the chimney of the boiler room will be as follows:

1+150/273=1,55
Vgas \u003d 10 * 10 * 1.55 / 3600 \u003d 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 arrangement of the chimney with complex calculations, you can use the standards developed by specialists:

for heating equipment with a power of 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 in the range of 3.5 kW - 5 kW, then the parameters of the chimney must be at least 0.14 * 0.20 m;
if devices with a power of 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 during the construction of the chimney the power of the heater is known, then to determine the cross section of the pipe, you can use the data calculated by specialists. If power 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 heater. The greater its power, the larger and more reliable the chimney should be. If the parameters of the device are unknown, and it is impossible to calculate the required values on your own, then you need to resort to the help of qualified specialists. Any mistake in the calculations can lead to the inoperability of the chimney or to the incomplete removal of harmful substances from the dwelling.

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 house is heat. The owner of the house has to solve the problems of heating a private house. For heating, which can be mounted independently (except for gas), including chimneys.

In order to ensure the complete removal of flue gases from the room, good draft and prevent tipping of the draft, it is necessary to comply with the requirements of regulatory documentation.

It is the chimney that ensures the safety of residents. An improperly designed chimney is unable to completely remove toxic combustion products (carbon dioxide and carbon monoxide, sulfur oxides), smoke and soot. Even a fire is possible if hot smoke enters the room. It is especially dangerous to overturn the draft - turn the movement of smoke in the opposite direction.

Therefore, when installing a chimney, it is necessary to correctly calculate its parameters - they are the ones that ensure the creation of ideal draft and complete removal harmful substances.

What parameters need calculation

The main parameters of any vertical chimney are the length and internal (working) section of the flue duct. All the information below is equally true for heaters 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 the 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 furnace. Therefore, the actual length of the vertical part of the chimney will be slightly less than the calculated data - by the distance from the bottom of the furnace to the outlet. This distance can be determined from the drawing of the unit or measured.

Do not think that lengthening the chimney is good. Thrust is based on the rise of hot exhaust gases, and if too great length pipes gases are cooled and thrust decreases. For the same reason, the chimney must be insulated. Even traditional furnace chimneys from red brick. The draft situation is aggravated by the fact that the exhaust gases from modern high-efficiency boilers have a low temperature.

With a moderately elongated chimney, the draft increases, while more heat escapes into the atmosphere. Too strong current of gases will extinguish gas heating units. .

Installing a low chimney in a residential building is completely unacceptable - there is no sufficient vacuum in it, the gases rise at a slower speed, due to which the draft decreases. It is allowed to install low chimneys on a separate standing ovens such as in the barbecue garden, etc.).

Chimney diameter

No less important for creating thrust and the diameter of the chimney. When installing modern heating units, the minimum diameter is determined simply - according to the unit's passport (and the diameter of the outlet pipe). In addition, the regulations provide minimum dimensions sections of chimneys corresponding to a unit of a certain power. These data are given in the passport of the unit.

If for some reason the internal section of the chimney is chosen to be square, then its area must be no less than a round structure.

When using an already existing traditional stove, the chimney is left the same. On device brick oven and a chimney with your own hands, you must use the project (preferably not downloaded on the Internet!) And lay out the pipe in strict accordance with the drawing. The same applies to free-standing brick structures.

Calculation methods

Professionals use several methods for calculating the parameters of the chimney. When installing large industrial pipes, designers are entrusted 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 inner surface of the hog;
meteorological situation in the region.

The calculation of large pipes is often a topic for thesis at University. Fortunately, the size of chimneys in a private house is smaller, the power of heating units is also inferior to industrial facilities.

When designing small pipe for a private house, they use simpler, albeit fairly accurate calculations. The parameters of the chimney obtained as a result of the calculations ensure the complete evacuation of combustion products from the furnace and ensure the safety of residents. Such calculations make it possible to avoid errors in the choice of parameters and during the installation of the chimney, to avoid subsequent alteration of structures. Such alterations in an already built and finished house are much more difficult than in 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 diameter of the chimney. Sauna heaters or garage oil stoves are usually also equipped with ready-made sandwich chimneys of small diameter (100 mm).

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 complicated and require the use of some special data, so let's consider the calculation for a heating unit (fireplace) on wood - they are often made original, relying only on the experience of the stove-maker, so the calculation of the 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;

the mass of firewood burning within an hour in the firebox - B = 5 kg / h (moisture content 25%);

outgoing gases temperature – t = 160°С.

Formula for determining the volume of outgoing gases:

where V is the volume of air required for the complete combustion of 1 kg of fuel. For firewood with a moisture content of 25%, 10 m3 of air is needed to burn 1 kg.

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 140 × 140 mm. The cross section of the pipe for a traditional stove should be over size blew one and a half times.

The volume of combustion products under normal conditions and the temperature of the outgoing smoke are normative data. See table:

Swedish calculation method

There is a so-called Swedish method of calculation, based on the choice of the height of the chimney, depending on the ratio of the hearth area of the furnace and the pipe section. The method is usually used for wood burning fireplaces. Calculate the ratio:

then the ratio is converted into percentages and according to the graph, depending on the resulting size and shape of the hog, the height of the chimney is selected.

When using the Swedish method of calculation, it is possible to calculate the cross-sectional area of the boron channel based on the hearth area 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 the parameters of the chimney

After the calculations, the height of the pipe is checked against the requirements of the regulatory document - it must not be lower than that required by SP 7.13130.2013. In any case, take the larger value of the length.

The best diameter of the chimney is the one corresponding to the passport of the heating unit.

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 high 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. Insufficient removal of flue gases reduces the efficiency of the boiler, stove or fireplace, there is a risk of carbon monoxide or carbon dioxide poisoning for residents and a fire hazard.

SNiP requirements

In accordance with SP 7.13130.2013, minimum height flue pipe from the head to the grate of the heating unit must be at least 5 m. flat roof its height must be at least 0.5 m. The maximum length of the horizontal section must 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 close to a tall building, a tree, or a low stand-alone chimney close to the house, these objects can block the wind from the chimney and reduce draft. To determine if the pipe does not fall into the zone of wind backwater, 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 must be above this line.

Choose the larger of the two heights. If, in order to comply with regulatory requirements, it is necessary to build a very high chimney (much higher than 5 m), then it will be necessary to install a chimney fan that provides sufficient draft for any length of the chimney.

Chimney height table above 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 defines the minimum sections of the chimney channel of a brick or concrete chimney depending on the power of the heating unit:

up to 3.5 kW - 140 × 140 mm (Ø not less than 158 mm);
3.5-5.2 kW - 140 × 200 mm (Ø not less than 189 mm);
5.2-7.0 kW - 140 × 270 mm (Ø not less than 219 mm).

When modernizing furnaces with an unknown power, either the chimney of the existing section is left, or a round stainless steel insert of a suitable diameter is inserted inside. If modern ceramic or sandwich pipes are installed to the old furnace, then the internal diameter of the modules must be no less than the diameter of the liner that would fit into the old pipe when installed. Theoretically, you can look for the design of the old furnace, but in most cases this is not possible.

Most often, a stove-maker was invited, and he folded stoves and chimneys of 2-3 mastered standard sizes without any projects and calculations. Really determine all the features of a brick oven device according to appearance impossible, and the only guide when choosing the section of the liner or a new chimney is the section of the flue of the existing chimney (provided that it worked well). If the chimney, then when replacing or upgrading it, it is better to invite a heating engineer and entrust him with the appropriate calculations.

Pipe diameter with inner surface from smooth ceramic or stainless steel may be slightly less (30%). In the valves of solid fuel stoves, there must be a non-blocking hole with a cross section of at least 15 × 15 mm.

The internal section of the chimney: which is better?

In a square or rectangular chimney, there will be smoke swirls in the corners, slightly inhibiting the flow of gases and contributing to the settling of condensate and soot. For the same reason, the corners of the pipe practically do not participate in the flow of gases. In addition, for square and rectangular hogs more area the surface of the walls than with round burrs - this increases the friction of the rising gases against the walls and slows them down more.

Therefore, it is advisable to choose a round chimney, and modern pipes made of sandwich or ceramics produce exactly round sections, like pipes made of stainless steel, asbestos cement. A square or rectangular shape is found on old brick chimneys. But for modern boilers, stoves and fireplaces, a round stainless steel insert must be inserted into the brick box.

What to do if the cross section of the chimney is square

But it is also possible to use a square-section chimney - a square or rectangular shape does not have a very significant effect on traction, and a complete alteration of the pipe is complex and costly. 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 an insert, it will not work for a long time - it will be destroyed by chemically aggressive condensate.

A brick pipe should have a cross section of about one and a half times larger than that of a round chimney with smooth steel walls. Therefore, the installation of the liner does not impair the smoke removal capacity of the square brick chimney.

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 outlet pipe of the boiler or slightly larger (if the pipe has a non-standard section).

The diameter of the chimney for the stove is determined from the cross-sectional area according to the eternal school formula: s \u003d πd2 / 4. The cross-sectional area should be equal to or slightly less than the value of the cross-sectional area of a square hog, determined according to 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 section of the hog, the higher the pipe should be. A taller chimney increases the draft and the rate of rise of the flue gases. But excessively high thrust begins to slow down - hot gases cool, they are also slowed down by friction against the walls of the hog, especially a rough brick one.

Calculation of the optimal thrust indicator

Draft - reduction of pressure in the chimney. The draft calculation is needed to check whether the height and cross section of the chimney flue are correctly determined.

where ∆P is the pressure difference at the inlet and outlet of the pipe, Pa;

a - Atmosphere pressure, Pa;

h is the height of the pipe, m;

Ti is the average indoor temperature, K;

To is the external temperature, K.

For a non-specialist, the draft indicator does not provide sufficient information, therefore, it is usually calculated the amount of exhaust smoke that is provided by the presence of draft in the chimney. It is the volume of exhaust gases that shows how much the pipe ensures the 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 is the sectional area of the hog, m2;

C is the coefficient taking into account friction losses; usually taken equal to 0.65-0.7;

g - acceleration free fall, 9.807 m/s2;

h is the height of the pipe, m;

Ti is the average indoor temperature, K (the temperature in kelvins is 273 units higher than the temperature in °C);

To is the external temperature, K.

Due to what natural draft is formed in the furnace

The natural draft in the chimney is due to the rise of hot and less dense smoke upwards. From below, dense cold air is sucked into the furnace, oxygen reacts with fuel, air with smoke is heated in the furnace, rises, and so on.

Calculation example

For example, I will show the calculation of the volume of air removed for a pipe with an inner diameter of 0.125 m, an area of 0.012266 m2 and a height of, for example, 6 m, an internal temperature of 20 ° C and a minimum external temperature of -20 ° C.

Conclusion: such a pipe ensures the complete removal of flue gases from the furnace. Vcalc noticeably exceeds Vref, therefore, to reduce the cost of the chimney, it is worth calculating Vcalc for a shorter or narrower pipe and considering the possibility of installing them.

When choosing a chimney with a smaller section and height, it is imperative to calculate the draft at 10 ° C - it will be less than at low temperatures, but Vish must be equal to or greater than Vcalc even at positive temperatures, otherwise complete evacuation of carbon monoxide and carbon dioxide from the room in warm weather will not be ensured.

In this case, Vcalc is much greater than Vout, since in the calculations we took a structure 6 m long (rather than the optimal 5 m) and rounded the calculated diameter of 0.118 m up.

Online calculators

Significantly facilitate the calculations of the parameters of the chimney ready-made online calculators.

Conclusion

I say goodbye to my dear reader. When will you build a new cottage or upgrade old house, Special attention pay attention to the design of the chimney - this is the key to the safety of your family. Receive new articles of the site, bring friends to the site, share interesting and useful information with social media followers.

It is also important to choose the right height and diameter of the chimney. An incorrect calculation of at least one parameter will affect traction and efficiency. Mistakes that can be made when designing and building a chimney in a residential building or bathhouse often lead to more grave consequences: fire, the need for financial costs for rework, etc. Therefore, it is so important to carry out regulatory requirements during pipe construction.

How to calculate the diameter of the chimney

When designing a chimney, it is necessary to choose the material to be used. And the material largely depends on what fuel will be used for heating. After all, the chimney is designed to remove the remains of the combustion of one fuel, and will not work with another. For example, a brick chimney works great with wood, but is not suitable for gas-fired heaters.

In addition, a correct calculation of the diameter of the duct pipe is required. If the chimney is used for one heater, the problem can be solved by viewing technical papers supplied by the manufacturer of the instrument. And if several are connected to one pipe different systems, then to calculate the chimney, you need knowledge of the laws of thermodynamics, professional calculation, especially the diameter of the pipe. It is wrong to assume that the diameter is needed more.

Swedish method

Among different ways calculating the diameter, an optimally suitable scheme is important, especially if the devices are low-temperature and long-term burning.

To determine the height, the ratio of the cross-sectional area of the chimney pipe to the internal combustion chamber is taken into account. The height of the pipe is determined according to the schedule:

Where f is the area of the chimney section, and F is the area of the furnace.

Let, for example, the cross-sectional area of the furnace F is 70 * 45 \u003d 3150 square meters. cm, and the section of the chimney pipe f is 26 * 15 \u003d 390. The ratio between the given parameters is (390/3150)*100%=12.3%. After comparing the result with the graph, we see that the height of the chimney is approximately 5 m.

Important! This calculation method is more suitable for fireplace appliances, because it does not take into account the volume of air inside the firebox.

Important! In the case of installing a chimney for complex heating systems it is important to calculate the parameters of the chimney pipe.

Accurate calculation

To calculate the desired section of the chimney, be sure to take into account all its characteristics. For example, you can perform a standard calculation of the size of a chimney connected to a wood-burning stove. They take the following data for calculations:

the temperature of the combustion waste in the pipe is t=150°C;
the speed of passage through the waste pipeline is 2 m/s;
the burning rate of firewood B is 10 kg/h.

If you follow these indicators, you can do the calculations. For this purpose, the amount of outgoing combustion products is calculated according to the formula:

Here V is equal to the amount of air required to burn the fuel at a rate v= 10 kg/hour. It is equal to 10 m³ / kg.

It turns out:

Then calculate the desired diameter:

Table of chimney diameters

Diameter tables compiled for various chimneys are now relevant, since many people prefer to install ready-made pipe elements from various materials. To easily understand these diverse materials and learn how to choose correct parameters, documents with normative data entered in special tables have been developed. Here are the relevant parameters. To calculate the required dimensions, you can use these tables.

Attention! It should be remembered that the cross section of the flue pipe must be greater than or equal to the cross section of the internal channel of the heater.

Accurate tables of calculated diameters of the flue pipe for its correct operation are calculated in accordance with technical parameters all elements, according to the recommendations of specialists, materials of the flue duct or using tables diameter - power.