Wrongly selected chimney-pipe oven leads to the fact that the smoke does not have time to be removed into the atmosphere and penetrates into the living room, creating a threat of carbon monoxide poisoning. If the channel cross section is too large, the flue gases cool down faster than they have time to leave the system, which causes the formation of aggressive condensation and the destruction of the internal structure. furnace. Ignoring the technical characteristics of the heat generator at the design stage often causes reverse traction, when the combustion products instead of going outside go into the room at the slightest wind.
The second extreme is the narrowing of the channel, which creates excessive aerodynamic drag and does not allow the furnace to operate at full capacity. In such a situation, the fuel burns inefficiently, more firewood or coal is consumed, and the walls of the channel are intensively growing. soot, increasing the risk of fire. Right. chimney-diameter This is a critical stage, which directly affect the safety of operation, the service life of the equipment and the economy of fuel consumption.
Effect of chimney diameter on traction and efficiency
The physics of the combustion process directly depends on how quickly the combustion products are removed from the furnace. Plunge in the chimney is created due to the difference in temperature and density of gases inside the pipe and air outside. If chimney-diameter When selected correctly, the optimal flow is created that carries the smoke away, but does not blow heat out of the furnace too quickly. Insufficient thrust leads to incomplete combustion of fuel, and excess - to a sharp decrease Efficiency The heat just goes into the pipe.
When designing, it should be borne in mind that the flue gas velocity should be in a certain range, usually from 1.5 to 2.5 m / s. Too high speed of noise and whistle in the pipe can not be avoided, and too low is fraught with smoke. Pipe section The volume of the furnace and the type of fuel used must be appropriate. For solid fuel boilers and furnaces, the requirements are stricter than for gas boilers, due to the greater volume of combustion products and the presence of solid particles.
⚠️ Note: Operation of the furnace with impaired traction is prohibited. Constant smoke of the room indicates a critical error in the calculations of the cross-section or clogged system.
The temperature of flue gases also plays a role: the hotter they are, the higher the thrust, but also the higher the thermal insulation requirements of the channel. Pipe diameter It affects the cooling rate of gases: in a wide pipe, gases contact the cold walls longer and cool faster, which can lead to a stop of the natural traction process. That is why for different types of fuels there are standards and recommendations for cross-section.
The main factors in the choice of a pipe cross section
Choosing the right channel size is not just a mathematical problem, but a comprehensive analysis of operating conditions. The first and most important factor is the power of the heat generator. The greater the volume of the furnace and the higher the performance of the furnace, the more gases are formed per unit time, and the wider should be the amount of gas. chimney. Manufacturers of equipment always indicate the minimum permissible diameter in the technical documentation, and it is impossible to deviate from these values in a smaller way.
The second important aspect is the height of the pipe. The two parameters are interrelated: if the pipe is low, the diameter must be larger to provide the same traction, and vice versa. However, there are limit values: excessive increase in the cross section at low altitude will not give a result, since the gases will cool. The material of manufacture is also taken into account: brick channels have a rough surface that creates vortices, so for them the cross section is often done slightly more than for smooth ones. steely Or ceramic pipes.
- 🔥 Type of fuel: firewood, coal, pellets or gas require different rates of gas removal.
- 🏗️ Furnace design: The presence of turbo deflectors, boars or heat exchangers changes aerodynamics.
- 🌡️ Flue gas temperature: determines the need for insulation and affects the flow density.
- 🌬️ Wind rose and location of the house: affect the pressure on the head of the pipe.
It is also important to consider the number of corners and curves of the track. Each 90 degree turn is equivalent to adding a specific square of straight pipe in resistance. If the track is difficult and has many knees, chimney-pipe It is recommended to take with a margin to compensate for pressure loss. The smoothness of the inner walls also matters: corrugated pipes create more resistance than smooth-walled ones.
Methods for calculating chimney diameter
There are several ways to determine the size of the channel. The simplest and most reliable is the use of ready-made compliance tables developed on the basis of many years of practice and standards. However, for non-standard designs or unique stoves designs, a more accurate engineering calculation may be required. The calculation formula is based on the channel capacity and the volume of fuel burned.
For round pipes, the cross-sectional area is calculated by the formula of the circle area, and for rectangular ones, by multiplication of sides. Calculation of diameter Often lead from the boiler power: for each kilowatt of power requires a certain cross-sectional area, which depends on the type of fuel. For solid fuels, this figure is higher.
Formula for indicative calculation
Diameter (mm) ≈ 1.6 * √P (kW) for solid fuel. It is a simplified formula that gives a basic understanding of scale, but for an accurate design, altitude and temperature must be taken into account.
In the case of The sandwich tube is an internal section, and the calculation is carried out precisely on it, ignoring the thickness of the insulation. If you use a brick chimney, its internal section should be at least 140×140 mm for most household stoves. In the case of installation of a gas boiler, the requirements may differ, since not only the thrust, but also the speed of condensation is important there.
| Furnace power (kW) | Min. round-pipe diameter (mm) | Min. brick-channel cross-section (mm) | Type of fuel |
|---|---|---|---|
| 3.5 | 140 - 150 | 140 x 140 | Wood/Coal |
| 3,5 - 5,0 | 150 - 180 | 140 x 200 | Wood/Pellets |
| 5,0 - 7,0 | 180 - 200 | 200 x 200 | Solid fuel |
| up to 24 (gas) | 120 - 130 | 140 x 140 | Natural gas |
Standard sizes and marking of pipes
The market offers a wide range of ready-made solutions, and chimney-pipe standardized for ease of installation. The most common steel pipes with an external diameter, multiples of inches or standard millimeter values. When buying it is important to distinguish between the external and internal diameter, especially when it comes to multi-layered structures.
For single-circuit pipes, the size is indicated by the outer diameter, which is simultaneously working. In the event sandwich-structure The marking often contains two values: internal diameter / external diameter. For example, the entry "115/215" means that the working section is 115 mm, and the outer dimension with insulation is 215 mm. The first number (115 mm) is used for thrust calculations and adapter selection.
- 📏 Standard internal diameters: 80, 100, 110, 115, 120, 130, 150, 180, 200 mm.
- 📐 Steel thickness: for solid fuel furnaces, it is recommended that steel not less than 0.8-1.0 mm.
- 🔗 Docking: The pipes are connected by the socket ("by smoke" or "by condensate"), which also affects the permeability.
When choosing system components, pay attention to the quality of the weld. It should be smooth, without influxes, which can become a place of soot accumulation. Pipe size It should be selected so that all elements of the system (revisions, tees, deflectors) have an identical internal cross-section. A narrowing of the channel even in one area can negate the effectiveness of the entire system.
☑️ Checking before buying pipes
Features of round and rectangular sections
The choice of channel shape affects the aerodynamic characteristics. The round section is considered ideal from the point of view of physics: flue gases spiral in, creating a stable thrust, and the absence of angles prevents the formation of swirls and stagnant zones. Diameter of round pipe provides maximum throughput at a minimum perimeter, which reduces heat loss and the amount of condensate.
Rectangular and square channels, often made of brick or prefabricated blocks, are less efficient. At the corners of these channels, turbulence zones are formed, where the flow slows down, which contributes to precipitation. soot and creosote. In addition, with the same cross-sectional area, the round pipe has a smaller perimeter, and therefore a smaller contact area with cold air, which improves thermal performance.
⚠️ Note: When transferring a rectangular brick channel to a round sleeve, the area of the circle should be at least the area of the rectangle. Reduction of the section is unacceptable.
If you use chimney with a rectangular cross-section, the corners should be rounded as much as possible when laying or use special liners. The aspect ratio of the rectangle is also important: it is not recommended to make the channels too elongated, the optimal aspect ratio is 1:1.5. The closer the shape is to the circle, the better the system works.
Installation rules and typical errors
Even perfectly calculated. pipe-piece It will not save the situation if the installation is made with violations. One of the most common mistakes is to use pipes of different diameters in different areas without smooth transitions. Steps inside the channel create powerful swirls that extinguish the traction and accelerate the overgrowth of soot.
It is also important to ensure the tightness of the connections. The chimney is a system that operates under dilution, and any cold air pump through the looseness can upset the temperature balance and stop the movement of gases. All joints should be tightened with clamps and, if necessary, misstated with heat-resistant sealant. Pay special attention to the places of passage through the floors and roof.
Tip: To clean the chimney, provide a tee with a condensate collector and an audit door at the bottom of the vertical section. It'll make it easier to maintain.
Do not forget the height of the pipe above the roof ridge. Even the correct diameter will not provide traction if the header is in the zone of the wind support. The pipe should rise above the skate at least 0.5 meters (at a distance to the skate up to 1.5 m). Compliance with these standards guarantees the stable operation of the furnace in any weather.
The main conclusion: The diameter of the chimney must strictly correspond to the power of the furnace and the type of fuel. No arbitrary change of section is allowed during the course.
Frequent Questions and Answers (FAQ)
Can a pipe larger than the outlet of the furnace be used?
The use of a pipe of larger diameter is possible, but undesirable without the installation of a special sliver regulator (latch). Excessive cross-section will lead to a decrease in flow speed, cooling of gases and a drop in thrust. If there is no other way out, the diameter can be increased by no more than 15-20%, and you will need to adjust the air supply.
How often should you clean the chimney with the right diameter?
With the right diameter and the use of high-quality dry fuel preventive cleaning is recommended 1-2 times a year (before the heating season and after it). If raw wood or coal is used, the frequency of inspections increases to 3-4 times per season.
Does the pipe material affect the choice of diameter?
Yes, it does. Bricks. The channels, due to roughness, require a cross section about 10-15% more than smooth steel or ceramic pipes of similar length. Steel and ceramics provide better traction with smaller dimensions.
What if there is no thrust even with the right diameter?
It is necessary to check the height of the pipe above the skate, the presence of a deflector cap, the tightness of the joints and the temperature of the incoming gases (heating of the pipe). Also, the reason may be the lack of air flow into the room or the work of powerful exhaust ventilation in the house.