Chimney: basic rules for design and installation

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Correct installation of the chimney is a prerequisite for the normal functioning of the fireplace, stove or boiler. This article indicates the basic installation rules and calculation principles used in the design and installation of chimneys.

Chimney: basic rules for design and installation

The desire to build a house on their own arises, as a rule, due to the need to save material resources, because the services of specialized enterprises are not cheap. However, the construction of a chimney requires a special approach: you cannot do without the use of special knowledge in this matter. Therefore, let us recall the basic rules for creating effective smoke exhaust systems and the importance of observing them..

Chimney installation rules: what should be the correct chimney

Fuel consumption, the amount of heat loss, fire safety and air quality in the heated room depend on how correctly the chimney functions. Therefore, its design and installation should be carried out in accordance with SNiP “Heating, ventilation and air conditioning”, DBN V.2.5–20–2001 Appendix G “Removal of combustion products” and other regulatory documents. Let’s talk about how a properly designed and installed chimney should be – these are the basic rules for its creation.

The material from which it is made has a great influence on the characteristics of the channel for the removal of combustion products. In new buildings, as a rule, pipes made of acid-resistant stainless steel containing molybdenum are installed. But for stoves and fireplaces working on wood and coal, ceramic bricks are also quite suitable..

Chimney: basic rules for design and installation

It is preferable that the cross-section of the chimney is a regular circle: this shape creates the least resistance to the outgoing smoke. The height and section of the chimney is calculated in accordance with building codes, further this will be discussed in more detail.

The correct approach to the horizontal sections of the canal is important: they should not be longer than 1 m, otherwise soot will be deposited and traction will weaken.

The connection of the heating unit to the chimney pipe often has to be carried out when the diameters in the connection zone do not match. To solve the problem, a reduction adapter is used. All joints are carefully sealed.

Chimney: basic rules for design and installation

The pipes are connected in such a way that their extensions are directed upwards. This prevents condensation and resins from flowing out along the outer wall of the pipe..

A brick chimney is being built according to the project: the order of masonry must be prescribed for each layer. In this case, one should strive to obtain an inner surface with a minimum of roughness and achieve complete tightness..

Chimney: basic rules for design and installation

An old brick chimney can be used with a new gas boiler only after the sleeve has been completed: an acid-resistant steel pipe is inserted into the middle of the channel, leaving a small gap.

Chimney: basic rules for design and installation

Most flue gas systems must be fitted with a cleaning inspection.

Thermal insulation of external pipes is mandatory: this will not only eliminate condensation, but will contribute to the fastest heating of the pipe.

When passing the channel through the ceilings, it is necessary to take measures to isolate the heated parts from combustible materials.

The outer part of the pipe is securely fixed and protected from the wind. The upper part is closed from atmospheric precipitation with weather vane or deflectors. An exception is gas equipment: in this case, the installation of a protective cap is a violation.

What is the wrong chimney

It is very difficult and expensive to correct the mistakes made during the construction of the chimney, and sometimes it is impossible at all without dismantling the old system. Here are examples of the most common mistakes and their consequences:

  1. The use of materials not intended for the construction of chimneys. So, for gas boilers, the use of bricks is unacceptable: the acid contained in the combustion products will destroy it within several years. You can also not use asbestos-cement pipes: when heated, they collapse. Plastic also cannot withstand high temperatures.
  2. Errors in choosing the diameter of the pipe and calculating the height of the chimney threaten the lack of normal draft and low efficiency of the system.
  3. Excessive loads on the base of the chimney can lead to its destruction..
  4. Poor thermal insulation is the reason for the formation of condensation and ignition of nearby materials.

Chimney height: depending on the angle of inclination of the roof and the distance to the ridge

Ceramic bricks, previously used for the construction of chimneys, are increasingly being replaced by systems from other materials. The most commonly used steel pipes: uninsulated and insulated. In this case, the option without insulation can only be used for internal installation – in a specially constructed mine. Outdoor installation of the pipe requires mandatory insulation, otherwise the formation of condensation on internal surfaces is inevitable.

Chimney: basic rules for design and installation

In order to determine the height of the chimney for an industrially manufactured boiler, you should use the formula: h (m) = (? p? Tp? Tn) / (3459? (Tp – 1.1? Tn)), Where ?p (Pa) – static thrust, Tr – average temperature in the middle of the pipe (in Kelvin), Tn – average outside air temperature. Pipe temperature (Tr) can be recognized on the basis of measurements at the outlet of the boiler and is indicated by the manufacturer in the technical passport of the heating equipment. In this case, natural cooling is taken into account for each meter of the chimney: in a brick – 1 degree, in an insulated steel – 2 degrees, in a steel without insulation – 5 degrees. Outside temperature (Tn) should be summer: at this time the thrust will always be weaker than in winter.

However, the results of calculating the height of the chimney in some cases need to be corrected, but only upwards. The fact is that the house itself sometimes turns out to be higher than the obtained value of the chimney height. In this case, the rule is that:

  • a chimney located at a distance of up to 1.5 m from the ridge must be at least 0.5 m higher than it;
  • if it is located within 1.5–3.0 m from the ridge, then its top should not be lower than the ridge;
  • at large distances from the chimney outlet to the ridge, the height of the pipe is chosen so that it is not lower than the line drawn from the top of the house down at an angle of 10 degrees.

Chimney height above the roof

For solid fuel and gas boilers, the chimney height must be at least 5 m: usually, manufacturers indicate this parameter in the accompanying documentation. It should be remembered that a high pipe should be fastened additionally – with the help of guy wires.

Chimney: basic rules for design and installation

But that’s not all: if there is another, higher building next to the house, then the chimney must be brought out above the roof of the neighboring building..

Cross-sectional area

The value of this parameter can be calculated by knowing the height of the chimney h (m) and the heat load of the burner according to the formula: S = (K? Q) / (4.19? Vh), Where TO Is an empirical coefficient numerically equal to 0.02–0.03, and Q (kJ / h) – device performance specified in the passport, h (m) – chimney height.

If it is easier to act, without formulas, then the following values ​​should be taken as a basis for the cross section of the smoke exhaust duct made of bricks (the cross section of the round ducts should be of exactly the same area):

  • for a unit with a capacity of up to 3.5 kW – 140 × 140 mm;
  • for power from 3.5 to 5.2 kW – 140 × 200 mm;
  • for power from 5.2 to 7.2 kW – 140 × 270 mm.

Chimney: basic rules for design and installation

A significant excess of the calculated value leads to a deterioration in traction and, as a result, to unstable operation of heating equipment. A smaller diameter threatens with poor removal of carbon monoxide and other combustion products and even the complete cessation of this process.

Additional requirements for chimneys for stoves, fireplaces, solid fuel, gas boilers and gas water heaters

Some rules not mentioned previously that should be followed:

  • the use of a solid fuel stove requires mandatory compensation of exhaust ventilation using a supply ventilation;
  • chimney ducts can be located in the outer walls if they are built of non-combustible materials, but at the same time, external insulation should be provided to prevent condensation;
  • for each stove (if they are located on different floors) a separate pipe is provided, but it is allowed to use one pipe for two stoves located on the same floor: at the joints of the pipes, cuts are installed with a height of 1 m or more, and a thickness of 12 cm;
  • brick smoke channels should be built with pockets for cleaning, which are closed with bricks laid on an edge and covered with clay mortar (doors can be installed);
  • if necessary, deviations of pipes from the vertical by an angle of up to 30 ° and a section length of no more than 1 m are allowed, while the channel cross-section must be the same;
  • if the roof is made of combustible materials, a mesh spark arrester is installed in the upper part of the chimney;
  • between chimneys made of brick or heat-resistant concrete and roof parts made of combustible materials should be equal to or more than 130 mm, for ceramic uninsulated pipes – 250 mm, for them with insulation – 130 mm;
  • the top of the chimney for the fireplace is protected with a weather vane or fungus;
  • two devices operating on gas may be connected to a common duct for the removal of combustion products, if these devices are located no further than 750 mm from each other;
  • the cross-sectional area of ​​the chimney connected to the gas appliance should not be less than the cross-sectional area of ​​the gas outlet of the appliance itself, while the upper part of the pipe is not covered with a visor.

Chimney: basic rules for design and installation

Information from regulatory documents establishing rules for the design and installation of chimneys

Frost-resistant clay brick is suitable for laying chimneys. It is strictly forbidden to build channels from cinder-concrete and other similar materials..

For connecting gas appliances to chimneys, connecting pipes made of galvanized or roofed steel with a thickness of 1 mm or more are suitable. You can also use flexible metal corrugated pipes that come with the equipment. In this case, it is important that the connecting pipe has a vertical section, the length of which from the lower level of the branch pipe to the axis of the horizontal section of the channel should not be less than 0.5 m.If the ceiling height is less than 2.7 m, this distance may be halved – for equipment equipped with traction stabilizers and up to 0.15 m – for devices without stabilizers. The total length of horizontal sections in new-built houses should not be more than 3 m, for old buildings 6 m are allowed. It is necessary to observe a slight slope of the pipe towards the heating device.

The flue ducts should not have more than three turns, while the radius of curvature should be equal to the diameter of the pipe. It is forbidden to lay a chimney through living quarters.

How to care for your chimney

If the thickness of deposits on the inner surface of the pipe exceeds 2 mm, it is time to start cleaning. You can get rid of dense dirt with a scraper and a stiff brush with a long folding handle: as you move deeper into the channel (work starts from the top), the length of the handle is increased.

Chimney: basic rules for design and installation

The combustion hole must be closed from below: this will prevent soot from entering the room. In addition, it is advisable to cover furniture with foil, lock doors and windows. During operation, you can use chemical detergents, for example, “miracle log”, which emit a special non-toxic gas during combustion, from which carbon deposits lag behind the pipe surface.

There are also effective folk remedies. For example, it is sometimes recommended to heat the stove with aspen wood: this creates a high flame, which burns out deposits on the pipe walls. But this should be done carefully: a large amount of soot can cause a fire. You can also burn potato skins: the steam generated is effective against soot deposits.


The requirements set out in the article are mandatory. Otherwise, the chimney will be ineffective and even dangerous. This information will serve as a useful reminder for those who already have some experience with chimneys. For those who do not own it, the material of the article should convince of the need to take seriously the details of the process of creating a chimney. Do not overestimate your capabilities: in order to avoid annoying mistakes, you should seek help from professionals.

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