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Construction of a chimney is an extremely important and responsible task, during which the likelihood of any errors and omissions should be minimized. Incorrect design inevitably entails significant losses of time and money for reconstruction, which is simply impossible not to do, because this can lead not only to poor draft, but also to a fire or carbon monoxide poisoning.
Key points in chimney design
At the chimney design stage, you should first decide on the material from which it will be made. The choice of material, in turn, largely depends on what fuel the heating device will operate on. For example, a chimney made of brick is ideal for wood-burning stoves and fireplaces, but is categorically not recommended for use with gas boilers.
It is extremely important to correctly calculate the cross-section of the chimney, its diameter and height. If you make a mistake when choosing one of these parameters, this will inevitably affect the efficiency of the entire heating system, or even lead to more serious consequences.
Can a chimney be universal?
One of the most important points in the process of designing and building a chimney is the choice of material for it. Today there are a large number of companies on the market offering modern chimney systems, which, according to them, are suitable for use in any conditions and with any heating equipment, regardless of what fuel it runs on. However, in reality this is nothing more than a marketing ploy, since such universal systems simply cannot exist. Of course, individual chimney systems are capable of functioning quite well under different conditions and using different fuels, but in this case there can be no question of compliance with all standards and requirements.
How to choose the shape of the internal section of the chimney?
To determine the optimal shape of a chimney, you need to understand the principle of its operation. The fact is that its walls heat up unevenly, and therefore the smoke, rising upward, twists along the central axis. Based on this, it is easy to assume that the most suitable chimney shape is cylindrical.
When using chimneys with a rectangular cross-section, turbulence will inevitably arise, which serves as an obstacle to normal draft, and sometimes even appears. At the same time, the higher the speed of the thrust itself, the stronger the turbulence is formed, and the worse the process of gas movement proceeds. This nuance must be taken into account when calculating the chimney draft, since in principle a rectangular shape is acceptable, but only for those heating devices that do not require strong draft to operate. Moreover, such chimneys also have their advantage - they retain heat longer than cylindrical pipes, therefore, with the correct design for traditional stoves and fireplaces, rectangular chimneys are the best choice. At the same time, for modern heating boilers operating on the “stop-start” principle, it is advisable to install cylindrical pipes. When using such boilers, savings are achieved due to faster heating of the system to the desired temperature, since after this they go into standby mode. And faster heating is ensured thanks to strong draft, which is possible precisely in the case of using cylindrical chimneys.
Calculation of the internal diameter of the chimney
In order to correctly calculate the chimney diameter for a particular heating device, first of all you should read the manufacturer’s instructions; if there are none, then it is recommended to adhere to the following rules.
When determining the cross-section of a chimney pipe for a fireplace with an open firebox, it must be taken into account that the ratio of their diameters should be 1 to 10 if a cylindrical chimney is used. The diameter of a square chimney should correspond to the diameter of the firebox in a ratio of 1 to 1.5. In this case, the diameter of the chimney cannot be smaller than the diameter of the blower. The level of heat transfer should also be taken into account: if it is 300 cal/hour, then the minimum diameter of the chimney should be 140x140 millimeters. The successful functioning of the entire heating system largely depends on how correctly the cross-section is chosen.
Calculation of chimney height
Another important question to consider during the design process is how long should the chimney be? To answer it, several factors must be combined and analyzed.
As you know, warm air rises. At the same time, as long as it is in the pipe, it remains warm, which means it continues to rise. As soon as it leaves the chimney, it immediately cools down and stops rising. Thus, the longer the smoke remains inside the pipe, the higher its temperature will be, and the greater its volume will rise upward, thereby creating draft. It turns out that the volume of the chimney directly affects the amount of air rushing upward and creating draft. The volume, in turn, depends on both the height and the dimensions of the internal section of the pipe.
Based on the foregoing, it turns out that if you have, say, a five-meter cylindrical chimney, it is enough to increase its internal diameter to improve draft. In reality this is not the case. Due to the increase in the internal diameter, the cooling of the flue gases in the pipe will occur much faster. This effect can be compared to pouring hot tea from a cup into a flat saucer.
Calculation of the chimney diameter and its height must be made in accordance with a number of rules, as well as taking into account the technical characteristics of the materials and the building itself. To more accurately calculate the height, you can use special programs that reduce the likelihood of error to a minimum. The chimney pipe should not be below the level of the ridge, as this will lead to the formation of turbulence.
Thus, the height of the chimney should be calculated individually, because in order to select the optimal size, you will have to take into account a number of parameters, including the distance from the window to the chimney and from the chimney pipe to the vertical axis of the ridge, the angle of inclination of the slope, the thickness of the roof, etc. . In this case, the height is determined without taking into account the protective umbrella of the chimney.
How to connect a collective chimney
Sometimes circumstances dictate the need to use one chimney simultaneously for several heating devices. In such cases, special attention must be paid to the correct calculation of all parameters (such as the maximum length of the horizontal section of the chimney, its height, diameter, etc.). This calculation is made taking into account what heating devices are planned to be used in the system, their type and power, as well as the fuel on which they will operate.
Let's say a boiler from a common heating system and a traditional fireplace will be connected to a single pipe. It is clear that these are fundamentally different heating devices, one of which runs on natural gas, and the other on wood. Accordingly, the recommendations regarding the chimneys used with them are radically different (read: ""). Is it possible to combine in this case? Practice shows what is possible. Let's look at how this happens.
As you know, the diameter of a chimney for a fireplace is calculated based on the fact that it should be a tenth of the diameter of the firebox. Naturally, this size will be excessive for the boiler. In this case, it is worth paying attention to the fact that, as a rule, people use the fireplace only from time to time, while the boiler works constantly during the cold season. In this regard, you might think that you should make it with a smaller diameter. However, such a step would be fundamentally wrong. In those moments when the boiler works independently, of course, no problems will arise, but as soon as you light the fireplace, increased aerodynamic resistance will inevitably arise in the chimney, regardless of the length of the horizontal section of the chimney located in the attic. As a result, heating appliances will not work properly, and carbon monoxide will begin to leak into the room.
The solution to this seemingly intractable problem is to use a two-pass chimney.
The main advantages of chimneys of this type include:
- the possibility of their use in conjunction with various heating devices, both individually and connected simultaneously;
- ensuring stable operation of each device;
- savings on construction and installation costs;
- space saving.
Possible chimney diagrams, look at the video:
During the installation process, it is necessary to comply with all the conditions for ensuring the correct operation of each device, and also strictly follow the preliminary calculations, so that later you do not have to think about how to lengthen the chimney or increase its diameter. When installing a brick chimney, you need to take into account that in order for it to be compatible with the boiler, there must be a liner that protects the brick from the negative effects of condensation.
Chimneys for hearths are very different, but their shape, dimensions of the fireplace pipe, material of manufacture and appearance do not matter, since the main requirement for the smoke exhaust structure is to ensure good ventilation of the combustion chamber.
Chimneys for brick fireplaces
It is believed that a chimney system is made with high quality only when there is no smell of smoke in the room where the fireplace is located, and the firewood in the firebox ignites immediately. If a chimney for a brick fireplace is installed in a private household, a chimney is usually built, which is combined into a single structure with a ventilation riser. Red solid ceramic bricks are used for masonry.
When constructing a smoke exhaust structure, it is necessary to adhere to a number of rules:
- To lay the masonry you need to use a lime-sand mixture.
- When a chimney system is inserted into a wall, regardless of what material it is made of, it is questioned. At the same time, they adhere to a 30-centimeter step, the anchors are inserted into the walls, adhering to a checkerboard pattern, to a depth of 20 centimeters, using reinforcement with a cross-section of 1 centimeter.
- To increase the stability of the masonry of the ventilation riser and chimney, it must be reinforced every third row using class A1 reinforcement with a 6-mm cross-section.
Disadvantages of brick structures
A smoke exhaust pipe for a brick fireplace has disadvantages, the main one being the short service life of such structures, which does not exceed 7 - 10 years. The fact is that frequent and significant temperature changes during the cold season lead to the appearance of condensation, and it either freezes or thaws. As a result, over time, the brickwork begins to collapse.
To reduce the impact of negative aspects you can:
- expand the cross-section of the external chimney walls to 25 centimeters in those places where they are above the roof surface;
- insulate these sections of the chimney with mineral slabs.
The chimney pipe will last longer if you install a cap on top of it, which will protect it from precipitation.
One of the significant disadvantages of brick chimney structures is the presence of a rough inner surface, since this circumstance leads to a decrease in draft efficiency compared to smooth pipe walls.
Designing smoke drainage through a chimney that has a certain reserve cross-sectional area can help cope with this problem. The installation of galvanized steel pipes inside the smoke exhaust system will also increase the service life.
Fire safety of chimneys
When arranging a smoke exhaust structure, one should not forget about fire safety rules:
- A gap of more than 25 centimeters is left between the wooden roofing parts and the inner surface of the chimney.
- Wooden parts must be insulated using felt, which is moistened with a solution of clay or laid in two layers of asbestos cardboard. Read also: "".
Stainless steel smoke exhaust structures
Chimneys for fireplaces of this type are stacked structures. The length and diameter of a stainless steel fireplace pipe can be very different. Such products are often produced complete with ceramic ones and placed inside steel ones.
Chimneys made from galvanized stainless steel have the following advantages:
- they can be installed without a foundation, since they are light in weight;
- assembly and installation of the structure is permitted after completion of construction;
- they are cheaper in cost than block and ceramic systems;
- If necessary, replacing individual elements will be easy.
Block ceramic chimneys
The basis for the ventilation ducts in such a ceramic chimney are blocks made of lightweight concrete. A wide range of these products allows you to easily select the required parameters.
To connect the blocks, a vertical reinforcement process is used. A ceramic fireplace pipe is inserted inside them and thermal insulation made from non-combustible materials is placed.
The technology for carrying out installation work in this case depends on the features of the structure being installed and therefore the use of generally accepted rules will be inappropriate.
The advantages of this type of chimney for fireplaces include:
- quick installation and assembly;
- long service life;
- high efficiency;
- a wide selection of blocks to give the smoke exhaust channels the desired configuration;
- the ability to clean the smoke exhaust system through special openings. Their presence at the bottom of the structure also helps condensate to drain freely.
The disadvantages of a ceramic pipe for a fireplace chimney include:
- relatively low price;
- long delivery times, since such structures are in most cases produced abroad.
Even taking into account the shortcomings, ceramic fireplace pipes are considered the undisputed leaders among similar products.
Criteria for choosing a smoke exhaust pipe
When deciding which pipe should be near the fireplace, first of all you should pay attention to the cross-section. The choice of this parameter depends on the type of unit or fireplace. The chimney is equipped taking into account the parameters 140x140, 140x270, 270x270, which are multiples of the dimensions of the brickwork.
The diameter of the fireplace chimney cannot be less than this parameter at the boiler outlet. And it, in turn, depends on the type and power of the unit.
The opening of the ventilation riser is located close to the chimney structure. According to the standards prescribed in SNiP, a hood is installed for boiler rooms, which is capable of providing three air exchanges per hour. For living rooms with fireplaces, ventilation is sufficient, creating twice the value of this parameter. The best solution would be to place the fireplace chimney surrounded by ventilation ducts.
Among other criteria, when calculating a chimney for a fireplace, the type of fuel used is taken into account. If it is liquid or gaseous, then its wall thickness should be at least 0.6 millimeters. When it is planned to use solid fuel, the required wall thickness of the structure is 1 millimeter.
When installing a chimney inside a brick shaft, single-wall components are used. If the smoke exhaust structure will be located separately in the house or outside the building, it is necessary to use insulating materials that ensure fire safety. When you plan to burn a fireplace in a wooden house with coal, choose chimneys with an insulation thickness of 50 to 100 millimeters.
When purchasing elements for installing ceramic or steel smoke exhaust systems, you need to pay attention to the permissible temperature limits. If you plan to use wood or coal for the fireplace, then you cannot use pipes that are designed for fuel combustion temperatures up to 250°C - they are intended exclusively for gas or oil units.
When choosing a chimney, pay attention to the following points: can it be used in stoves operating on solid fuel, and resistance to possible ash combustion at temperatures close to 1000°C.
The chimney for the boiler should look like a vertically located homogeneous structure. The height of the fireplace pipe cannot be less than 4-7 meters with an optimal draft of 10-20 Pa (more details: " ").
According to the operating requirements, cleaning of chimneys and monitoring their condition must be carried out by chimney sweeps at least 4 times a year.
The question of how to calculate the diameter of the chimney is in itself provocative. I immediately want to ask in response - Why? But we won't do that. Any purchased boiler, fireplace, or gas convector has an outlet for combustion products, which is indeed most often round. And here a chimney made of steel, or indirectly, made of ceramics, glass or asbestos cement, is already connected. Therefore, in fact, calculating the diameter of the chimney is not required. It is already specified by the design of the device itself. You cannot take pipes smaller than the output size, and larger ones are simply not worth it. You will need a gearbox, but this is an extra expense and no one needs it. It is better to make sure that the initial section above the heating device is vertical. As a last resort, it is permissible to install a bevel at an angle of about 45 degrees, which already goes into a pipe built into the wall or taken out.
When it may be necessary to calculate the chimney cross-section
- oven ordering;
- fireplace arrangement;
- ordering a barbecue and everything in the same spirit.
With a high degree of probability, something you need will be found. For example, that stove maker from Izhevsk on his website osnovaremonta.ru lists hundreds of ready-made designs that are just waiting to be brought to life. We don’t know why the resource has such a strange-sounding address, but it’s actually full of useful videos that will show you how to do masonry in this or that case. Please note that the seams are carefully bandaged, it is explained how to divide the brick, how many halves, quarters and other pieces are needed. This is just a great course. Moreover, the choice is really great.
We took from the resource the most interesting points from our point of view so that readers would bother searching only after preparing in advance. The diagram below completely indicates the rules for choosing the cross-sectional area of a chimney of various designs. This is not applicable only to closed systems where air is supplied separately, for example, from the street. But in this case, the easiest way is to use forced oxygen injection, as in condensing boilers, or copy an existing factory design.
At the very top of the graph there are three types of sections:
- Round.
- Square.
- Rectangular.
- On the x-axis we see a certain ratio that is obtained by dividing the area of the chimney by the area of the portal. To get percentages, multiply the quotient by 100.
- The minimum height of the pipe at which the structure will be sound is set along the vertical axis.
An example of calculating the cross-section of a chimney and choosing its shape
Let's say we have a fireplace. The portal of which is 8 bricks high and 3 bricks wide. This in centimeters turns out to be approximately 75 x 58 cm. In this case, the size of the channel is equal in area to just a brick. Which is 12.8 x 25.8 cm. We draw your attention to the fact that the dimensions may vary for products from individual factories, so please check the data before laying by thoroughly examining the order and taking the actual dimensions. Now let's do the math:
- The letter F indicates the area of the fireplace portal; it is equal to 75 x 58 = 4350 square centimeters.
- The small letter f denotes the cross-sectional area of the chimney, meaning its internal passage part. This will be 12.8 x 25.8 = 330.24 square centimeters.
For example, it is planned to build a two-story mansion, which has a height of 11 meters from the fireplace to the chimney cap. In this case, the percentage area ratio should be no lower than 8.4%. Since you hardly want to change the design, we select the appropriate chimney diameter for the fireplace. In particular, the pipe area will be equal to:
f = Fх 0.085 = 370 cm2, from where we find the diameter:
D= √4 x f / P = √4 x 370 / 3.14 = 21.7 cm.
- Glass.
- Ceramics.
- Steel.
- Asbestos cement.
An example of a chimney design for a purchased gas fireplace
The optimal chimney diameter for a fireplace is already indicated in the passport. On the back wall or on top there is a pipe for installing a standard section. But what about the height of the pipe? But no way, the manufacturer has already done everything to make the device work. Just follow the installation recommendations that come with the instruction manual. This usually concerns a straight vertical section above a heating device. Most often, the minimum length is regulated. If this rule is broken, then the craving will disappear. Combustion products will go into the room. As for boilers, they most often have a combined hood. This is when there is a coaxial pipeline, usually air enters through the outer pipe, and combustion products are removed through the inner pipe.
The diameter of the chimney for a gas boiler is strictly defined. While the oxygen moves towards the firebox, it still has time to heat up a little, which generally increases the efficiency of the device. Condensing boilers operate somewhat differently. They most often have separate hoods. In this case, air is forced in from the street by a fan, and the combustion products are cooled on a heat exchanger through which, for example, water flows until most of the condensate is removed from the flow. It is believed that this occurs approximately at the border of 30 ºС. This does not mean that you don’t have to insulate the pipe at all, but the danger of blocking the passage with an ice plug really decreases.
The diameter of the chimney for a solid fuel boiler is calculated by the designers and carries the least danger. Although distilling coal or wood (if they are raw) at low temperatures also gives little pleasure. We have already talked about what creosote is and why it is better not to deal with it directly. It is clear what the diameter of the chimney should be, but there is one more nuance: the chimney pipe should be fluffed along the passage of floors. This is a thickening of brick that reduces the range of fluctuations and the temperature value at the point of contact with the ceiling. In the case of a steel chimney, a box is used, which is filled, for example, with expanded clay. It is allowed, using adapters, to insert one segment of an insulated version, like Vulcan, in this place.
The diameter of the chimney pipe for the bathhouse is not so important, because the firebox is usually closed (for safety reasons), and the supply channel goes outside. Much more attention should be paid to the correct connection of pipes. A narrow subsequent one is inserted into the wide upper part of the pipe. This ensures that creosote does not leak into the piped water tank. And it will just become easier to breathe.
We hope that we have answered the question of how to calculate the diameter of a chimney pipe. When laying across floors, please note that with significant heat losses due to thin steel, condensate can form an ice plug at the outlet. At the same time, a chimney built into the wall is also not the best option, because a lot of heat is transferred to the atmosphere. Use extended structures. The distance from the chimney to the wall is about 40 cm, the material is asbestos cement or steel. Read above about the limitations of both options.
That's all for today, ask questions in the comments. We say goodbye until next time!
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Many owners of private houses dream of a fireplace - this personification of special comfort, conducive to a quiet, comfortable holiday in the winter cold. Such a dream can be brought to life - by purchasing a ready-made factory-made fireplace, or by building a “classic” brick structure.
If you purchase a finished product, then no special problems are foreseen - the manufacturer has already provided to the smallest detail the dimensions of the device itself and the diameter of the chimney pipe required for it. With a brick fireplace, everything is somewhat more complicated, especially if the owner himself decided to take on its design. Many dimensional nuances must be taken into account, and one of them is the optimal cross-section of the smoke exhaust channel, on which both the efficiency of the fireplace and ensuring the safety of its operation depend. The calculator for calculating the cross-section of a fireplace chimney, located below, can help with this question.
The second subsection of the publication will provide several necessary explanations for the calculations.