Any autonomous device for space heating requires a device to remove toxic products of combustion of fuel. Furnace chimneys can have a different design, height or diameter, and during their construction, a number of technological nuances and features must be taken into account.

The construction of a chimney is the most important stage in the construction of a brick oven, the correct implementation of which depends not only on the efficiency of its work, but also on the well-being of the residents of the house.

The chimney is the most important part of the looped system, the correct operation of which directly affects the performance and efficiency of the furnace. The cycle of operation of such a system can be described as follows:

• Fuel combustion takes place in the furnace.
• During the combustion process, oxygen is processed, and caustic gases are heated and removed through the chimney to the outside.
• When the combustion products are removed in the furnace, an area of ​​\u200b\u200blow pressure is formed, where new portions of oxygen are drawn through the same chimney.
• The process is repeated again and again, until the complete combustion of the fuel.

Failure to comply with the chimney installation technology can cause a violation of the cycle and provoke some unpleasant consequences:

• Irrational fuel consumption.
• Deterioration of heat transfer of the furnace.
• Increased fire hazard.
• Penetration of dangerous carbon monoxide gases into the dwelling.

Varieties

There are several types of chimneys. They are classified depending on the location relative to the furnace itself:

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The worst thing for any "sandwich" type chimney is a soot fire, in which, in a short period of time, there is a sharp jump in temperature in the chimney to values ​​above 1000º C ( heatstroke).

In operation, each linear meter of the inner pipe may increase in length as a result of thermal expansion. up to 10 mm, and when soot ignites - up to 18 mm(Almost twice as much!). In this case, the outer pipe practically does not change in length. For example, with a steel chimney 10 meters high, the inner pipe can “climb out” upwards beyond the outer pipe. by 18 cm! When cooling down, the sections of the inner pipe cannot return to their original position due to friction against the insulation and the lack of communication between them, socket connections may be broken and fistulas may form. If, structurally, the inner pipe cannot expand upwards, then under the action of thermal linear expansion it develops into an "accordion", the structure of the metal changes, when cooling, internal fistulas are also formed between sections of the working pipe. In the future, such steel chimneys represent fire hazard and gradually burn out.

The ceramic chimney pipe is also subject to destruction.. The actual ignition of soot occurs almost instantly and is accompanied by a phenomenon similar to a strong bang and a flash. As a result of a very fast and sharp increase in temperature from a working value of 200-400ºС to 1000-1200ºС ( temperature shock) Maybe cracking already fragile ceramic pipe, especially in places of internal stresses or shocks received during transportation and installation. In practice, when soot ignites, the most common problems are with by breaking off the branch pipe on ceramic tees ceramic channels.

The causes of soot fires are related with the quality of firewood and missing the deadlines for cleaning the smoke channel. And since this is not so rare, a requirement began to be presented to metal chimneys - soot fire resistance.

According to this criterion, chimney pipes are divided into two classes: soot fire resistant and soot fire resistant. The term "soot fire resistant" in relation to chimneys means resistance to single soot fire. Such chimney pipes retain tightness and consumer properties after soot fire. BUT the next fire of soot is detrimental to them. Therefore, European regulations for metal chimneys resistant to soot fires provide replacing pipes after a soot fire. Russian standards do not yet impose on their chimney manufacturers the requirement of resistance to soot ignition, such tests are not carried out.

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Stove heating, although it is a thing of the past, is still quite relevant in our time. Stoves are still used in baths and saunas, and fireplaces are increasingly being installed in private homes. That is why the installation of a chimney on the roof requires a special approach and attention.

Types of chimneys

Chimneys can be made of metal, brick, asbestos cement and sandwich pipes.

According to the place of installation, chimneys can be classified into:

• wall. In this case, the pipe is located in the main wall of the house, regardless of whether it is internal or external;
• mounted - the pipe is mounted directly on the furnace and is displayed strictly vertically;
• suspended - the chimney is fixed outside to the wall using brackets or other fasteners;
• indigenous. In this case, the chimney is a separate structure.

Requirements for chimneys

The chimney must meet certain parameters:

The height of the chimney above the roof should not be lower than a certain mark, since it is this parameter that largely affects the traction force. But more does not mean better, because when excessive, hot gases begin to cool sharply, as a result of which condensation forms on the inner walls of the chimney.

The cross section of the pipe must correspond to the dimensions of the firebox. The larger it is, the stronger the fire and thus more smoke. For its unhindered passage, it is necessary to organize a larger section of the chimney pipe. With insufficient size, smoke begins to enter the room. If the pipe has a cross section much larger than the furnace, then this leads to a decrease in traction and an increase in the amount of condensate on the walls. With a high level of heat transfer from the pipe, the smoke rising through it cools very quickly, which leads to a decrease in thrust.

Installation of a chimney on the roof

Before starting work on the arrangement of the chimney, it is necessary to determine the material, the main requirement for which is resistance to high temperatures. So, the inner surface of the pipe must be able to withstand heat of 1000 degrees for 30 minutes and 500 degrees - with a constant fire. Gases rising up the pipe can have a much lower temperature (about 300 degrees).

The heat resistance margin is necessary in order for the chimney to be able to withstand the ignition of soot deposited on the walls of the pipe. The outer part of the chimney should not heat up above 90 degrees, and in places of passage through flammable structures (roofing cake) - no more than 65 degrees. The sealing of the furnace must be airtight and fireproof.

Chimneys must maintain their strength even at high temperatures. So, according to fire safety standards, in case of a fire inside the house, the strength of the chimney should remain unchanged for 1.5 hours. In addition to resistance to temperatures, the material must be resistant to smoke. And that part of the chimney that rises above the roof must be resistant to negative temperatures.

All these requirements can be met by such material as brick. That is why it has long been used for the construction of stove chimneys. But bricklaying can sometimes be difficult and not every homeowner will be able to do this type of work on their own. Moreover, here it is necessary to apply knowledge not only of brick, but also of furnace work.

It should be noted that pipes for fireplaces and cooking stoves may differ in the degree of heating. In chimneys, the air and walls can warm up to 250-300 degrees, while in the fireplace this figure reaches 400 degrees. Therefore, to organize the chimney of the fireplace, it is necessary to use heat-resistant bricks made of fireclay clay. In this case, the wall thickness should not be less than 15 cm, and the seams should not be less than 5 mm. Because of this, the cost of building a chimney for a fireplace can increase markedly. In addition, the weight of the resulting structure also increases, which entails the need to lay a more solid foundation.

Stainless steel chimney

Modern has found wide application in the installation of gas boilers and in saunas. According to fire regulations, such chimneys must be insulated with a material that is resistant to high temperatures, since the surface of the pipe is very hot and can cause a fire. In addition, the steel is quite thin, which does not allow the pipes to withstand high temperatures for a long time. This is the main reason for the frequent breakdown of such chimneys.

Despite the fact that the inner surface of such chimneys is quite smooth and provides good protection against the accumulation of slag, condensation often forms in it, which over time can lead to corrosion of the material. In addition, the material of such pipes is too thin to withstand high temperatures for a long time. Therefore, such pipes fail rather quickly. Also, there is an abundant release of condensate in them, as the smoke cools quickly.

Sandwich pipe

Today, the use of double-walled pipes is becoming more and more popular. Sandwich chimneys are manufactured in factories, which allows you to strictly control the quality of products, but they are mounted without any special difficulties. Such chimneys are distinguished by high reliability and fire safety. In addition, they cope well with the action of an aggressive environment.

The inner chimney pipe is made of stainless steel. It is wrapped in a layer of thermal insulation, which in turn is protected by galvanized steel. Mount such a chimney in lengths of one meter. The advantages of sandwich pipes include the speed of assembly and ease. Due to the low weight, it is possible to save money on the construction of the foundation for the furnace. It also takes the minimum amount of time and effort for the chimney. In addition, the pipe has different diameters, which allows you to choose the necessary sandwich chimney for a specific firebox.

The disadvantages of such structures include high cost, short service life and insufficient sealing of the chimney on the roof. When temperatures change, the internal parts can move relative to each other, which leads to depressurization of the casing, and this can cause a fire. Manufacturers guarantee that sandwich chimneys can last up to 10 years.

We do not imagine homes without heating. Our concept of comfort unconditionally includes a suitable temperature regime. There is no central heating in a private house, and each owner has a heating problem.

We welcome our regular reader and bring to his attention an article about chimneys for stoves - an absolutely necessary component of any heating system, whether it is a stove, a modern fireplace or a boiler with automatic fuel supply.

Chimney - a vertically located pipe that discharges hot flue gases of the fuel in the heating unit into the atmosphere to a height sufficient to create draft in the duct and disperse toxic combustion products away from windows and ventilation ducts.

Principle of operation

The principle of operation of chimneys is based on the phenomenon of expansion of hot gases, a decrease in their density and, accordingly, the rise of lighter gases upwards.

Flue gases rise upwards, a rarefaction is formed in the furnace and colder air is sucked in - a draft phenomenon occurs.

How is the chimney

The main part of any chimney is a vertical pipe structure. Structurally different from modern prefabricated counterparts from prefabricated modules.

A traditional brick chimney includes the following elements: a neck for connecting to a furnace, a riser with valves, a slope, an otter, a neck (at the point of passage through the roof), a headband, and sometimes a metal cap.

Homemade chimneys made of metal or asbestos cement include pipes, caps, adapters for connecting to the furnace, and insulation.

The most modern types of chimneys are ceramic and made of. The ceramic structure consists of an external expanded clay concrete frame, an internal prefabricated ceramic pipe, and a layer of insulation between them. The ceramic and sandwich structures themselves include the following blocks: straight, for collecting condensate, tees, cleaning modules, transition elements for connecting heating units. An integral part of a modern chimney is a deflector.

Types and designs

The design features of the chimney primarily depend on the material from which they are made.

According to the material of the chimneys are:

• brick;
• reinforced concrete (usually industrial);
• asbestos-cement;
• of steel;
• ceramic;
• three-layer metal - two layers of steel with mineral wool insulation between them.

By design, chimneys are:

• indigenous - the design has its own foundation;
• wall, built into the bearing walls of the building;
• mounted - light pipes are mounted on a vertically located outlet pipe of a boiler or fireplace (and a potbelly stove);
• often lightweight structures are simply suspended from the supporting structures of the building;
• coaxial - arranged according to the "pipe in pipe" principle. The most common example is the horizontal gas outlets of gas heating boilers. It is used in devices with a closed combustion chamber and provides maximum safety for residents. Save fuel consumption. Recently, vertical structures of the Shidel system have appeared, taking air for combustion on the roof of the house (just below the head).

Which is better to choose

The choice of a chimney largely depends on the parameters of the installed heating unit (design, temperature, type of fuel used), the degree of readiness of the house (we are modernizing an old house with a stove and a wall pipe, the house is only “in the project” or the supporting structures have already been mounted, or there is already a finish) ; heated volumes.

Features of various types of chimneys are shown in the table:

Table 1

Name	Advantages	Flaws
brick	Robust and high temperature resistant masonry construction, durability depending on the liner material.	Difficult installation requiring highly qualified masons; heavy weight, the need for a foundation; long installation time, the need to replace the insert approximately every 10 years. When working with modern boilers and fireplaces, a brick without an insert can collapse in just 10 years. Wall structures can only be mounted during the construction of the house.
Ceramic	Service life up to 50 years, smooth inner surface, high installation speed; high acid resistance, good thermal insulation; withstand temperatures up to 550°	Expensive option; installation requires some qualification, there is a need for a foundation; fragility
Steel single-layer (and asbestos-cement)	Smooth inner surface, light, inexpensive, fast installation, easy repair; resistance to corrosion and condensation	Requires insulation; when passing through structures made of combustible materials, large retreats are necessary; they burn out in 10-15 years, there are no components - during installation you will have to do all the elements yourself. Galvanized will last five years (or less)
Steel type "sandwich"	Long service life, smooth inner surface, light weight, quick easy installation, easy repair, high resistance to corrosion and condensation; can be installed / hung outside the building; good thermal insulation	Fairly expensive items.

It is not worth using flexible steel corrugation - they burn out very quickly.

Despite the price, it is worth choosing modern ceramic chimneys or "sandwich". If necessary, they can be mounted both in the finished house and outside the house, they are durable, easy to assemble, resistant to high temperatures, well insulated, and have a large assortment of ready-made factory elements.

If you want to use an old wall box from a conventional heating stove, you need to insert a stainless steel insert and insulate it. But perhaps you should choose a sandwich - less hassle.

Do it yourself or order

You can do it yourself some elements for the installation of single-layer pipes or lay out a brick structure (if you have the skills of a qualified bricklayer).

But the installation of prefabricated structures - this will help save a considerable amount from the family budget. You will have to pay a lot for the services of a qualified team - the amount is comparable to the cost of materials. There is a risk of running into unskilled workers.

When deciding whether to do the work yourself, you need to carefully analyze your capabilities:

• how accessible is the roof;
• Do you have friends or relatives who can help?
• do you have a fear of heights;
• What are your qualifications in performing repair work.

Building regulations

The arrangement of chimneys is determined by the provisions of SNiP 41-01-2003.

The design of the chimney must meet the following regulatory requirements:

• the minimum height must be at least 5,000 mm or grate;
• when located on a roof slope at a distance of less than 1.5 m to the ridge - the pipe must be 500 mm higher than the ridge;
• when located on a roof slope at a distance of 1.5-3 m to the ridge - the pipe must not be lower than the ridge;
• when located on a roof slope at a distance of more than 3 m to the ridge, the angle between the horizontal and the line passing through the ridge and the top of the pipe should be no more than 10 °;
• the head should rise above the flat roof to a height of at least 1,000 mm;

• the maximum length of each horizontal and inclined sections should not exceed 1000 mm, the total length of their projections on the horizontal should not exceed 2000 mm. In the presence of oblique and horizontal sections, it is necessary to lengthen the pipe by the length of the horizontal projections. For ceramics, the presence of horizontal sections is not allowed.

Fire safety requirements for chimneys

The distance from the surface of chimneys made of ceramic, insulated steel and asbestos-cement to combustible structures of the house must be at least 250 mm; for brick chimneys and sandwich pipe structures - at least 130 mm.

It is necessary to protect building structures made of combustible materials with cement or gypsum plaster over a grid of at least 25 mm thick.

If the roof covering can burn (roofing material, shingles, ondulin), or leaves and fluff can accumulate on it, a mesh spark arrestor should be installed on the head.

Remember that the quality of smoke removal depends on the life and health of your loved ones.

Traction force

Factors affecting traction force:

• pipe height;
• the state of the surface of the internal channel - the regularity of cleaning from soot, the roughness of the walls;
• the presence of inclined or horizontal sections. The presence of horizontal and inclined sections is undesirable, since the lengthening of the chimney is undesirable - the gases will cool, the draft will decrease up to tipping over;
• deflector installation;
• quality of insulation;
• air supply to the furnace.

Your safety depends on the traction force, therefore it is necessary to regularly check the presence of traction and take measures to clean the channel from soot, the pipe head from ice.

Making and installing a chimney with your own hands

What materials are better to make

The easiest to install are steel structures. Single-layer steel products require insulation and the manufacture of components - in general, work for pathological workaholics, and here we will not consider their installation.

Installing a chimney from a sandwich pipe is quite simple, the presence of a large number of various elements and components in stores allows you to assemble a device of any configuration.

Drawing and diagrams

Before starting work, determine the dimensions and draw a diagram or drawing - this will help to correctly calculate the required amount of materials and properly organize the work.

Size calculation

The height of the pipe is determined in accordance with the requirements of SNiP 41-01-2003, but should not be lower than 5 m from the grate. The diameter is taken equal to the diameter of the outlet of the heater.

Installation video

Watch our video - it will help you see all the intricacies of the assembly process.

Mounting Features

Installation starts from the stove or fireplace. The first starting element is mounted on the nozzle of the boiler or furnace. This element does not have insulation for technological reasons (alt-free filler melts and sinters into stone). All elements are designed in such a way that one of its ends has a smaller diameter and is inserted one into the other, as into a socket. One of the docking options is to slightly pull out the inner pipe, insert it into another inner pipe. Press down. Then lower the outer pipe with insulation along it, press it down. Fasten the connection with a crimp collar, tighten it with a bolt and nut. All joints must be sealed with sealant.

Then a tee is mounted, modules with a cleaning hatch and a condensate trap are mounted from below. There are designs for installing the lower part of the chimney on the floor.

Then mount the rest of the structure. After a meter, the sandwich is attached to the wall with special brackets. An element with a cleaning hatch should be installed on each floor and in the attic.

It is advisable to connect the elements of the chimney “through condensate” - the pipes are mounted in such a way that the upper one is inserted into the lower one and the condensate cannot seep through the joints, but flows down the walls into the trap.

An element with a gate is mounted under the ceiling.

The passage of the pipe in the ceiling is covered with a galvanized sheet and filled with insulation. The distance to the structures must be at least 130 mm.

The most difficult stage in the installation is the passage of the roof. Mark the hole in the right place on the roof. Make a hole in the roof. A roof sheet is attached from the inside, a roof cutting is installed on the roof. It is selected depending on the angle of the roof. The cutting edges lead under a sheet of roofing material.

If necessary, install extensions. Install deflector.

Common errors and installation problems

The most serious mistake is the lack of a condensate collector and elements with cleaning hatches.

In places where structures pass through ceilings, it is strictly forbidden to install joints of individual elements - leaking hot smoke can cause a fire.

A very significant mistake is the absence of a deflector or at least a cap over the chimney.

Snow and rain should not get inside the pipe - they increase the formation of condensate, ice can block the cross section of the pipe.

Maintenance and cleaning

Any chimney requires regular cleaning of soot. This will avoid fires, reduce traction. Cleaning should be done twice a year.

There are two cleaning methods - mechanical and chemical.

With a chemical fire, special agents are burned in the furnace. They burn at a very high temperature and accelerate the wear of the inner walls of the chimney, so it is better to use mechanical cleaning methods for a sandwich.

Icicles and ice from condensate can freeze on the head - they block the section of the box and reduce draft, which increases the risk of carbon monoxide poisoning for residents.

It is necessary to choose pipes in which the thickness of the outer metal layer is 1 mm (and not 0.5 mm). It is very easy to check - for a product with a thin wall, the wall bends if you squeeze it with your hands.

When installing sandwich structures, it is necessary to use a special sealant for high operating temperatures (automotive sealant with an operating temperature of 500 ° is not suitable).

If the pipe rises above the roof by more than one meter, it should be reinforced with stretch marks.

Despite the wide range of modern and modern heating systems, solid fuel stoves are not going to give up their positions of popularity at all. This is understandable - the presence of such a heating facility gives a certain sense of autonomy - even under the most adverse circumstances caused by interruptions in the supply of other energy sources, a stove with a supply of fuel will help both heat the house and cook food for the family.

But the stove will only work efficiently and safely if it is designed, built or built to the right specifications. And one of the key conditions for the functioning of the furnace is a well-thought-out and reliable system for removing combustion products -. There are several options for the equipment of this system - from laying out a classic brick pipe "the old fashioned way" to the use of completely new, sometimes even unexpected technological solutions using modern composite materials. And at the peak of popularity in this matter in our time, probably, are sandwich pipes for furnaces.

What are sandwich pipes for furnaces, how they differ, what you need to know about their choice and the basic rules for designing a system - all this in this publication.

What are sandwich pipes and their main advantages

The developers of sandwich chimneys set themselves the task of minimizing the disadvantages that are characteristic of almost all chimneys, regardless of the material they are made of.

Any chimney is subject to negative destructive influence both from the inside and from the outside. The combustion products have a high temperature and a very aggressive chemical composition, which leads to erosion or corrosion of the materials of the internal channel. In addition, over time, the chimney channel becomes overgrown with soot, which reduces the patency of the pipe, and as a result, the efficiency and safety of the furnace.

Outside, in open areas, external factors act on pipes - high humidity, precipitation, fluctuations in air temperature outside. In addition, the temperature difference between the outside and inside the chimney leads to the active formation of condensate - and this, in turn, increases the likelihood of soot deposits.

"Classic" brick chimneys, although considered time-tested, have a whole "bouquet" of shortcomings.

• Firstly, the rectangular section of the channel is by no means optimal - unnecessary turbulence of the gas flow inevitably occurs in it. Reduce overall traction.
• Secondly, it is impossible to achieve ideal smoothness of the channel walls - the porous structure of the brick will still contribute to soot deposits.
• Thirdly, the brick chimney itself is a very massive structure, quite difficult to build and requiring a reliable foundation.

How to lay out a brick chimney

If this option is chosen, then a number of important rules must be strictly observed. How to fold a brick chimney on your own - in a special publication of our portal.

• And fourthly, even a high-quality brick is subject to erosion under the influence of a whole range of negative influences, and the picture of crumbling chimneys is by no means uncommon.

This means that in order for the chimney to be optimal, it must be made with a round cross section, smooth inner walls, from heat-resistant, erosion-resistant and corrosion-resistant material. and light enough not to weigh down the entire furnace structure. It would seem that modern types of stainless steels meet all these requirements. However, such a simplified scheme is impossible for a number of reasons:

• Any metal has a high thermal conductivity, and a high temperature difference inside the chimney channel and outside can have a destructive effect on thin walls, and most importantly, leads to abundant condensed water vapor, which is always contained in the combustion products.
• The rapid cooling of gases in open areas of the chimney will inevitably lead to a decrease in the draft of the furnace.
• The sections of the metal pipe located inside the building are heated to very high temperatures, and this is unsafe both from a fire point of view and from the standpoint of a high probability of accidental injury - a burn.

This complex of problems would be completely or to the maximum extent possible resolved by creating a sandwich chimney structure. The inner channel and the outer surface of this design are two separate metal cylinders separated by a layer of heat-resistant thermal insulating material with a markedly low thermal conductivity.

The inner duct must always be made of a special type of stainless steel, with a reliable welding of the seam - usually argon welding is used.

The outer casing is also metal, but options are already possible here. Of course, the most resistant to external influences will be a stainless steel casing. However, sometimes, in order to save money, they also purchase cheaper options in which the outer pipe is made of galvanized steel.

Mineral wool made of basalt fiber is most often used as a thermal insulation layer, as it is the most resistant to high temperatures. The high density of basalt wool (from 120 to 200 kg/m³) provides the necessary structural strength. The thickness of this layer can vary - from 25 and even up to 100 mm. It depends on the parameters of the heating equipment and, to a certain extent, on the climatic conditions of the region.

The great convenience of such a design is that it carefully considers the issues of mounting individual parts into a single system. For this, connecting nodes are provided in the form of sockets and narrowed sections, special clamps, stoppers, sometimes flanges, etc.

Such a chimney system for the furnace immediately acquires a number of important virtues :

• The mass of the entire chimney system assembly is not so large, that is, it will not be necessary to strengthen the foundation of the furnace and its structure, as is the case with a brick pipe.
• The chimney can be placed on brackets vertically along the outer wall of the building. And this is a simplification of assembly, especially when passing through floors, and a significant saving of usable space inside the premises.
• The system is very "flexible" in terms of the possibilities of its placement. Manufacturers provide a wide range of additional components and components that allow you to quickly and reliably assemble the chimney of the required configuration. It becomes possible to bypass possible obstacles without resorting to large-scale alterations in the design of the house.

• The temperature difference between outside and inside is compensated by a thermal insulation layer. This stability guarantees normal stable traction, and condensation and soot deposits are minimized.
• The outer surface of the sandwich pipe, when properly assembled, does not heat up to critical temperatures, that is, the safety of the chimney operation is significantly increased.
• The assembly of such a chimney, subject to all technological recommendations, is an accessible and intuitive event that does not require any special training.

Such chimneys also have certain limitations :

• A quality set will be quite expensive.
• Over time, under the influence of high and low temperatures, signs of depressurization may appear at the junctions of individual nodes - this requires special attention: regular checks and, if necessary, preventive maintenance.
• Limited overall service life. Despite the fact that high-quality stainless steel is highly resistant, aging processes also do not bypass it. As a rule, manufacturers guarantee up to 15 years of trouble-free operation of their products. However, any other chimney for such a period will most likely require some kind of repair and restoration work.

How to choose a metal sandwich chimney

As already mentioned, the cost of such a chimney system is quite high, and replacing low-quality pipe sections can result in considerable costs. Therefore, it is very important to be able to correctly evaluate products when choosing, so that disappointment does not come after one or two years of operation.

Selection criteria can be roughly divided into several categories. So, first of all, the quality of the materials used in the production of sandwich pipes is evaluated. The necessary linear parameters are selected - that is, the diameter of the chimney, the height of the future pipe, the thickness of the insulation layer. It is important to immediately think over the features of the structure being created in order to assess whether all the components are commercially available for its installation.

Assessment of the quality of manufacturing materials

To the untrained eye, all stainless steels look the same. The new pipe shines - but this is not at all a criterion for the quality of the metal.

The same “beautiful and shiny” pipe after a short period of time can be deformed and even simply burn through - alas, there is a lot of evidence of this on the Internet. And such a situation is a direct road to a fire or carbon monoxide poisoning.

Unfortunately, we have to state that the increased demand for such chimneys has also given rise to the "shadow sector" of their production, where materials are used that are of little use for such purposes. There is another situation when a perfectly high-quality sandwich was used in conditions for which it was simply not designed. For example, a pipe that is quite suitable for a gas boiler is unsuitable for use with a solid fuel stove.

Stainless steel grade

When choosing sandwich pipes, it is necessary to focus on the steel grade, which is used primarily for the internal channel. This parameter should be indicated in the passport documentation of the product, unless, of course, it is produced by a bona fide manufacturer. If the steel grade is not indicated, then it is better to look for another option.

So, the following grades of stainless steel can be found:

— AISI 430. Such steel belongs to the category of the most inexpensive. It is quite suitable for the outer lining of a sandwich, since its resistance to atmospheric phenomena is quite enough. But for the inner pipe, it is not suitable categorically. Its composition predetermines unimportant weldability, that is, it is very problematic to obtain a sealed seam. Such steel does not meet the requirements of increased heat resistance.

— AISI 439. This alloy is enriched with titanium additives, which significantly increases its resistance to corrosion and mechanical strength. Pipes made of such steel are quite suitable for any gas installations, as well as for solid fuel boilers and furnaces, but only for a small thermal power.

— AISI 316. This steel has a pronounced corrosion resistance to almost all aggressive substances. Thermal stability is average, so the pipe is only suitable for gas-powered equipment.

— AISI 304. Steel does not have the highest heat resistance, therefore it is usually not used by serious manufacturers from being used as an internal channel. Perfect for outer shells.

— AISI 321 and AISI 316i. They have excellent heat resistance and good ductility, easily amenable to high-quality welding. Such pipes are quite suitable for most types of boiler and furnace equipment, as they can withstand heating up to 850 ° C without deformation.

— AISI 310S. Fully versatile steel that can withstand temperatures up to 1000°C. It is quite suitable even for powerful solid fuel furnaces and boilers operating on the principle of afterburning pyrolysis gases. The only conditional drawback is the high price.

Knowing the parameters of your furnace, you can choose the optimal grade of stainless steel.

Do not forget about another way to check stainless steel. Of course, it will not give an accurate picture, but it will help you immediately avoid buying a low-quality fake:

It is necessary to take an ordinary magnet and try to “glue” it to the inner wall of a vertically standing sandwich pipe. The magnet should not be held - ideally it will just slide down. If it stays in place or goes down with visible braking, the “black” component of such steel is too high, and the pipe is unsuitable for a chimney.

Type of insulation material

As already noted, only basalt mineral wool should be used as an insulating material for the thermal insulation layer. In no case, no matter how attractive the price may seem, you should not purchase a sandwich pipe filled with glass wool. The coefficient of thermal conductivity of glass wool is no worse, then the heat resistance is completely different. At temperatures of about 300 ° C, its sintering begins, subsidence in size, and all its advantages are reduced to zero. In addition, fiberglass is very brittle, and the insulation layer does not differ in volumetric stability, it is prone to shrinkage.

In really high-quality sandwich pipes, manufacturers use heaters from leading brands - ROCKWOOL, PAROC and the like.

The diameter of the chimney channel and the thickness of the insulation

Manufacturers provide a fairly wide range of diameters. So, models are produced with an inner pipe from 110 to 300 mm, with different thicknesses of the insulation layer, that is, different external diameters of the structure.

The main parameters of a sandwich pipe are the diameter of the inner channel, the thickness of the insulation and, accordingly, the size of the outer casing

If new equipment, a boiler or a furnace is purchased, then the required diameter of the chimney pipe must be indicated in the passport data - this value should be followed. It is more difficult if the chimney is planned to be installed on a brick or home-made one - here it is important not to make a mistake with this parameter.

In this case, you can do it in several ways. The first, simple one, is to navigate according to the table showing the dependence of the thermal power of the equipment and the diameter of the chimney.

Thermal power of solid fuel furnace		Minimum section of a rectangular chimney	Pipe cross-sectional area	Minimum diameter of the inner pipe of a sandwich chimney
kW	kcal/hour
up to 3.5	up to 3000	140×140 mm	19600 mm²	158 mm
3.6 ÷ 5.2	3000 ÷ 4500	140×200 mm	28000 mm²	189 mm
5.3 ÷ 7.0	4500 ÷ 6000	140×270 mm	37800 mm²	220 mm

You can also focus on the approximate consumption of an existing furnace of one or another fuel. In this case, the following formula is used to calculate:

S = Vg /wg

S- cross-sectional area of ​​the chimney channel.

Vg is the volume of combustion products.

wg- the speed of movement of gases through the chimney (optimum is 2 m / s).

Thus, to calculate the diameter, it is necessary to apply the formula for the area of ​​a circle:

d = √4 ×S/π = √(4 ×Vg /wg) /π = √2 ×Vg /π

The value remains unclear. Vg. It is calculated as follows:

Vg = M × Vy × (1 +T / 273) / 3600

M- the total approximate mass of fuel burned in one hour.

Vy– specific volume of combustion products from combustion of 1 kg of fuel.

T- temperature at the outlet of the chimney

273 - the difference between the value of temperature zero in degrees Celsius and Kelvin.

3600 - the number of seconds in an hour, to bring the value to a single value.

So the formula looks like this:

d = √(2 × M ×Vу × (1 + T / 273) / (3600 × π))

Values Vy and T you can accept tabular ones using the table below.

Fuel type	Average calorific value of fuel, kcal/kg	Specific volume of combustion products from combustion 1 kg, m³/kg	Chimney outlet temperature, °С
Firewood, average humidity level 25%	3300	10	150
Peat lump or loose, air dried, humidity up to 30%	3000	10	130
Peat in briquettes	4000	11	130
Brown coal	4700	12	120
Coal	6500	17	110
Anthracite	7000	17	110

Surely, the formula will seem “heavyweight” to many, not conducive to independent calculations. To simplify the task, a calculator is placed below, in which the necessary arithmetic ratios are already laid down.