Chimney options for gas boilers. Chimney installation for a gas boiler: a professional approach

The chimney pipe, rising above the roof, is only a small visible structural element of a complex mechanism responsible for removing smoke and gas. Regardless of what fuel the heating equipment operates on (solid, liquid or gaseous), it must be supplemented with a system for removing combustion products. Every homeowner should have an understanding of the chimney structure in his home, which will allow him to properly operate the heating system in principle. For those who are yet to solve similar problems in arranging their home, before going to a specialized store or inviting professionals, we suggest that you first familiarize yourself with the theory. Let's take gas heating as an example. To begin with, at a minimum, you need to know what chimneys for gas boilers are, what their strengths and weaknesses are.

Types of chimneys: what will a specialist suggest?

Is it possible to install a chimney yourself? Of course! Although, if you have to do this work for the first time, then consulting a specialist will in no case be superfluous. But, one way or another, you still have to figure out what kind of chimneys for boilers exist at the moment.

So, you may be asked to choose one of the following options:

Option #1 - classic brick

Although they will offer you its construction, it is unlikely, since this is not even yesterday, but the day before yesterday. A brick chimney is characterized by a complex design, high cost and its construction takes a lot of time. In addition, in many operational characteristics such a chimney is inferior to more modern designs.

Option #2 - stainless pipe

Here the manufacturer offers a wide range of models. Among the advantages, one cannot fail to note the high resistance to mechanical damage and exposure to aggressive environments. A chimney for a gas boiler, made of stainless steel, is usually made in the form of a sandwich system - two pipes of different diameters, one inside the other. The empty space between them is filled with heat-resistant basalt wool.

The stainless steel chimney pipe is reliable and has a presentable appearance

Without exaggeration, today the installation of a chimney for a gas boiler using a stainless “sandwich” is one of the most successful solutions today.

Option #3 - coaxial chimney

It cannot be confused with another design; its distinctive feature is its presentable appearance. Although the operating parameters are at a high level. Moreover, the coaxial chimney for a gas boiler has a specific shape, on the inner walls of which condensation does not form. This point is very important especially for gas fuel heating systems.

Option #4 - ceramic design

It cannot be said that it enjoys great attention from the consumer audience in the luxury construction segment. And, where preference is given to simplicity and reliability, ease of installation and fire safety, and at all this an affordable price, a ceramic chimney has no alternative.

Whatever technology is preferred, in the end, installing a chimney for a gas boiler involves working with the following elements:

• An adapter connecting the heating boiler pipe and the chimney pipe.
• Feedthrough pipe.
• Telescopic pipes.
• The bracket and clamp are the main wall fastenings.
• Tee with revision - in the lower part there is a special fitting for removing condensate.
• Conical tip.
• Bends.

We invite you to watch an overview video with advice from a specialist:

What affects the efficiency of a chimney?

Perhaps the question is posed somewhat incorrectly from a professional’s point of view. Since the health and sometimes even the lives of people depend on the effective operation of the combustion product removal system, it is more advisable to consider the requirements for the chimney of a gas boiler.

A chimney of any design must be made in accordance with the requirements of SNiP 2.04.05-91, as well as DBN V.2.5-20-2001. Otherwise, the chimney will be installed incorrectly and the heating equipment will be connected to it. And this, in turn, calls into question the safety of operation of the entire heating system. These documents clearly regulate the design of boiler chimneys. These documents are subject to careful study, since violation of the standards set out in them will certainly lead to problems with the gas industry.

If we briefly outline the requirements for chimneys of gas boilers, then first of all you need to pay attention to the following points:

• Good traction is the key to efficient use of thermal energy from gas combustion.
• Correct design of the condensate collector - excess moisture should not accumulate on the walls of the chimney duct.
• It is prohibited to install deflectors, fungi, etc. on the chimney head. These elements reduce the efficiency of removing combustion products, and there is a risk of carbon monoxide entering the room.
• Requirements for chimneys of gas boilers require maximum attention to installation work. Particular emphasis should be placed on the tight fit of structural parts at the joints, that is, maximum tightness must be achieved. This will prevent hot gases from penetrating beyond the chimney.
• It is allowed to use common connecting flue pipes for several units.

From the outside it appears that the chimney is made of brick. In fact, it's just a decoration, and it's located inside the pipe

Algorithm for installing a chimney inside a building

Installation of a chimney for a gas boiler can be done both inside the building and independently (outside). You can understand what the difference is, while making certain conclusions regarding your specific case, from our small table.

As they say, draw your own conclusions.

We bring to your attention the internal structure of the chimney system. Briefly, this process consists of the following stages:

1. Applying markings in ceilings and roofing pie for holes for the chimney. We check the correctness several times.
2. Cut an opening for the pipe.
3. The pipe coming from the boiler is connected to the adapter.
4. The tee and revision are connected, the steel sheet is attached, and the main bracket is installed.
5. The pipe is extended, if necessary, “knees” are used.
6. For installation through ceilings, a special pipe is used.
7. A sheet of galvanized steel is placed on the pipe, in which a hole of a larger diameter than the chimney pipe is previously made. Galvanization is fixed to the ceiling.
8. To strengthen the joints, clamps are used, which are tightened with bolts or high-quality wire.
9. The chimney itself is attached with wall clamps, step - 2 m, as well as brackets, step - 4 m.
10. To complete the design, a special cone-shaped tip is provided.
11. The chimney is insulated.

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D To remove combustion products inside the furnaces of heating devices, chimneys for a gas boiler in a private house of different designs from different materials are used. The standards SP 7.13130 ​​specify the requirements for cross-sections, heights, location of chimneys, safe diagrams of passage units through structures made of flammable materials.

Chimney from a gas boiler on the facade of the house

Requirements for chimneys and installation rules

Combustion products have high temperatures, so chimneys must fully comply with the standards of SP 7.13130. The use of factory products that have not passed the Russian Federation certification is not allowed.

The main provisions of the set of fire safety rules are:

• internal cross-section of the chimney - 14 x 14 cm - 14 x 27 cm depending on the thermal power of the boiler (3.5 - 7 kW, respectively) for concrete, brick, ceramic structures, the area of ​​round or asbestos-cement pipes must correspond to these dimensions;
• height – 5 m minimum from the firebox to the deflector;
• chimney thickness - 6 cm for heat-resistant concrete, 12 cm for ceramic brick, not standardized for asbestos cement, sandwich.

The height of the deflector (an umbrella structure that protects the pipe from rain and wind) relative to the ridge depends on the distance of the chimney from it:

• 0.5 m higher at a distance within 1.5 m;
• level with the ridge at a distance of 1.5 - 3 m;
• at the level of an imaginary line at an angle of 10 degrees relative to the horizontal, drawn from the ridge to the pipe, at a distance of more than 3 m from it.

When moving the chimney outside, elbows are allowed within 1 m from the axis of the main pipe to the side at an angle of less than 30 degrees relative to the vertical. The cuts should exceed the thickness of the floors with decorative ceiling cladding by 7 cm with an even distribution of this size from below/top.

The distances from the outer surfaces of structures to wooden elements of load-bearing structures (sheathing, rafters, beams, crossbars) must be greater than the specified dimensions, depending on the chimney material:

Attention! It is prohibited to combine chimneys with ventilation ducts without a special design. But you can run combustion products from two boilers into one pipe if necessary.

Chimney structures

When choosing a chimney or channel, you should focus on the best combination of construction budget, resource, and maintainability. Depending on the materials used, chimneys for a gas boiler in a private house are attached with clamps to the enclosing structures or rest on separate foundations.

In all vertical structures, a serious problem is the formation of condensation, which is released when hot gases come into contact with the cold walls of the pipes. In coaxial modifications, which are often located horizontally, this disadvantage is absent. In addition, it is enough to give the pipe a slight slope towards the ground so that possible condensation drains out of it without additional costs.

Related article:

Installation of a chimney for a gas boiler in a private house is carried out according to the general scheme for asbestos-cement, sandwich, and ceramic pipes. For coaxial aluminum and plastic pipes, a circuit is not needed in principle. When making masonry from blocks, modules, and bricks, standard masonry techniques are used.

Sandwich installation

Chimneys made of two pipes of different diameters, inserted into one another, with a heat insulator between them, are called sandwiches. The design allows you to reduce the external temperature of the walls (increased fire safety), eliminate the formation of condensation (useful for increasing the service life).

A sandwich chimney of a wall-mounted gas boiler is installed in a private house using two technologies:

• for condensate– the upper elbow is inserted into the socket of the lower one; when condensate drains in the interpipe space, its penetration into the channel and ignition are prevented;
• by the smoke– the upper pipe is put on the lower one, preventing the penetration of combustion products into the room.

Attention! Gas boilers have gases with low temperatures at the exit from the combustion chamber. Therefore, the “condensate” technology is used.

The chimney assembly technology looks like this:

• installing a damper on the boiler outlet pipe to adjust the cross-section of the chimney channel;
• installation of pipes until they are blocked by condensate;
• making a cutting from a steel box attached to the floor from below;
• cutting through the chimney, building up to the roof;

• fastening to the canopy sheathing - a plate with a conical pipe located at the desired angle to it, depending on the slope of the slopes;
• fixing the sandwich chimney pipe to the roof with a okapnik (a conical clamp of a complex profile), which decorates and seals the joint.

After that, it remains to install one of the elements at the mouth of the pipe:

• volper - deflector for increasing traction with a flat cover;
• weather vane - deflector to improve draft of the original design;

• fungus – conical nozzle for protection from precipitation.

These elements are made of stainless steel and fully correspond to the style of sandwich chimneys.

Stone and brickwork

Chimneys for a private house can be built into brickwork (only into a load-bearing internal wall) or made from blocks. Domestic manufacturers produce several types of chimney modules:

• concrete - used only in conjunction with ceramic pipes running inside them, the outer surface is square, the inner is round;

• ceramics - pressed into special molds, then fired in kilns, have the design of an internal pipe, an external square thin-walled box, connected by stiffening ribs.

The Ukrainian company Schiedel produces chimney blocks made of volcanic pumice. The modules are called Isokern and are a budget option for individual developers. The material is much lighter than concrete and ceramics, the only drawback is the rough inner surface and the lack of Russian certificates. Regional fire safety services accept structures made from this material in 50% of cases.

Brick chimneys are built into walls during the construction of enclosing structures. To lay the blocks, it is necessary to concrete a separate foundation. But, the pipes can be placed in any convenient place, there are no problems with the passage units, rafter systems, or floors.

Asbestos cement pipe

Aggressive advertising by manufacturers of sandwich chimneys cites the main disadvantage of asbestos - the lack of environmental safety. In fact, only safe raw materials and technologies are used in domestic production. According to reviews from craftsmen who install all types of modern chimneys, an asbestos-cement pipe has the following advantages:

• is self-supporting - no need to attach to walls;
• does not condense moisture - there are no leaks into the combustion chamber;
• resistant to combustion products - the resource is higher than that of concrete and brick;
• cheaper than ceramics - the cost is much lower.

Installation of an asbestos cement pipe is extremely simple:

• the first pipe is installed on the foundation, secured with racks or a frame;
• the chimney is increased to the required height, the pipes are connected with couplings;
• The top is covered with a deflector, and a hatch is made at the bottom to install the cleaning door.

The connection from the boiler is made with a steel elbow, which can be replaced if necessary.

Installation of coaxial structure

Unlike other chimney modifications, a coaxial pipe can only be used for closed combustion chambers. (supercharging) is a mandatory operating condition of the system. The design of a coaxial chimney is similar to a sandwich, but instead of insulation, there are jumpers between pipes of different diameters. The inner pipe is used to remove combustion products; the street air necessary for burning natural gas is sucked into the interpipe space.

Unlike conventional chimneys, the pipe does not need to be pulled vertically across all floors. Instead, a 90-degree outlet is put on the outlet pipe, a coaxial chimney is attached to it horizontally, and goes out through the nearest wall while maintaining fire safety distances:

• maximum length of horizontal part 3 m;
• minimum 0.2 m to the ceiling, floor, ground;
• more than 30 cm from the axis of the chimney to the wall surface;
• at least 60 cm from the mouth of the pipe to the opposite wall.

The coaxial structure can be installed vertically above the roof, horizontally through the wall, or connected to a smoke duct built into the brickwork of the wall.

conclusions

Thus, for closed combustion chambers, a coaxial chimney is preferable, saving the construction budget and the aesthetics of the roof, in which there will be no holes. The most reliable for open fireboxes are asbestos-cement pipes or sandwiches. The most discreet wiring is ensured by built-in smoke channels in brickwork, structures made of concrete, ceramic blocks or Isokern modules made of volcanic pumice.

In new private houses equipped with heating boilers, they are installed to remove flue gases. traditional brick chimneys, and also increasingly used chimney systems made of steel or ceramics.

Which chimney should you choose? How to properly make a chimney for a boiler in a private house? Where can I buy quality chimney pipes of steel?

For a solid fuel boiler - a brick chimney

A brick chimney is usually costs less, than modern chimney systems. A traditional ceramic brick chimney pipe can easily withstand high flue gas temperatures. The pipe can even withstand ignition of soot accumulations in the chimney.

A brick chimney for a boiler in a private house is a rather heavy structure. The chimney is located on the foundation or a solid reinforced concrete floor. The construction of such a chimney requires certain skills; it is better to entrust the laying of a sealed and durable chimney to a qualified stove mason.

Channels and chimneys and ventilation are often placed in a brick chimney

The chimney is laid from high-quality solid ceramic bricks of a grade not lower than M125 using ordinary masonry mortar. The upper section of the pipe, above the roof, can be laid out of facing or clinker bricks. The thickness of the chimney walls must be at least 120 mm(half a brick).

The size of the chimney and ventilation channels is chosen as a multiple of the brick size, taking into account the thickness of the vertical joints. For example, the channel cross-section can be 140x140 mm(1/2x1/2 brick) or 140x200 mm(1/2x3/4 bricks), or 140x270 mm(1/2 x 1 brick). In practice, a smoke channel is often made measuring 20 x 20 cm(3/4x3/4 bricks). If necessary, it is easy to select and insert a round steel or ceramic liner of the appropriate diameter into such a channel.

The flue gases in the chimney duct should not be very cool. Therefore, they try to build the chimney into the masonry of the internal wall of the house or attach it to the wall. Sections of the chimney that pass through an unheated room (attic) or outside the house insulated with mineral wool.

Brick the chimney serves reliably and for a long time only at high flue gas temperatures, which prevents condensation from forming in the pipe. As a rule, this condition is met when the chimney is operated with a conventional one.

When working with modern gas or liquid fuel boilers, as well as with solid fuel pyrolysis boilers, pellet and others, operating for a long time in a slow burning mode of low intensity, the brick chimney is destroyed quite quickly.

Modern boilers are designed so that the exhaust gases have a fairly low temperature. As a result, condensation of water vapor contained in the flue gases occurs in the chimney. The pipe walls are constantly moistened. In addition, when combining with other combustion products, water forms aggressive chemical compounds on the inner surface of the pipe.

In particular, the exhaust gases of boilers contain sulfur, which, interacting with water, forms sulfuric acid in the chimney, which corrodes its walls. External signs of destruction are dark wet spots on the outer surface of the brick pipe.

The operating mode of a solid fuel pyrolysis boiler also contributes to the formation of aggressive condensate in the chimney, which quickly destroys the brick chimney.

Rough chimney walls contribute to the accumulation of solid soot particles on them. The roughness of the walls and the rectangular shape of the chimney duct make it difficult to clean the chimney from deposits.

For connecting gas and other boilers with low flue gas temperatures to a brick chimney, in a brick channel it is necessary to place an insert - a steel or ceramic chimney pipe.

A chimney made of ceramic pipes is a universal solution for a boiler in a private house

Chimneys made of special ceramic chimney pipes can be used for all types of boilers. The material is resistant to high temperatures and to any aggressive chemical compounds that can form in the chimney during the combustion of different types of fuel. This type of chimney is the most durable.

Ceramic chimney pipes are distinguished by the permissible maximum temperature of the exhaust gases.

For safe operation of a gas boiler, it is necessary to ensure complete removal of combustion products. If the chimney diameter is incorrectly selected, they can enter the room, which will lead to carbon monoxide poisoning. The danger is aggravated by the fact that combustion products are odorless and colorless, so it is impossible to determine the location of the leak without a special device.

The durability of the channel depends on the material. It must withstand high temperatures, moisture and acid produced during gas combustion. The material should be chosen light enough so that you do not have to strengthen the walls and foundation of the building. For production are used:

1. Stainless steel– resistant to most types of corrosion, not heavy, considered the best option. Provides reliable traction for 15 years.
2. Aluminum- also durable, but due to low mechanical strength it is used only for interior decoration.
3. Enameled pipes– are produced with built-in thermal insulation, which simplifies the installation of the chimney.
4. Cink Steel– will last a maximum of 5 years, as it will lose its tightness under the influence of fumes of high acidity.
5. Ceramics– the service life of such products reaches 30 years. European manufacturers reinforce them with beautiful steel frames. However, due to the heavy weight, sometimes it is necessary to take measures to strengthen the walls and foundation. Such structures provide maximum traction only in a vertical position, which is not always possible to realize.
6. Sandwich chimneys– consist of two pipes inserted into one another, with insulation between them. Due to 2 layers of metal they are highly reliable. Durability depends on the material of the inner tube. No additional insulation is required during installation.
7. Coaxial chimneys- also consist of two pipes, but the space between them is used to supply air to closed-type gas boilers from the street. They are produced in modules, convenient for quick assembly.
8. Brick chimneys- turn out to be heavy, so they require a foundation. Due to the rough walls, the draft is not at its best, which leads to the accumulation of soot on them. Therefore, the pipe will have to be cleaned twice a year. In addition, brick is hygroscopic, absorbs condensation and quickly collapses. But a preserved chimney can be used as a protective frame if you insert a stainless steel pipe into it with a condensate collector at the bottom.
9. Asbestos cement channels- cheap, but rarely used, as they are prone to cracking and releasing carcinogens when overheated.

Depending on the installation method, chimneys can be external or internal. Which one is better to choose depends on the type of building and location of the boiler. External channels lead horizontally to the street and are attached to the external wall. They are easier to install; you just need to follow the fire safety rules when arranging the hole if the house is built from flammable materials. However, careful insulation and installation of a condensate collector will be required.

The internal chimney is discharged through the ceilings and roof, which is not always acceptable in multi-story buildings. Installation is complicated by the installation of several special passage units that ensure fire safety.

Calculation of the chimney cross-section for a gas boiler

To accurately determine the parameters of the system through which combustion products are removed, complex calculations are made. This takes into account the shape and material of the pipe, the average temperatures outside and inside, the roughness of the walls, and more. However, the cross-section of the chimney (F, m²) can be calculated with sufficient accuracy for practical purposes using the formula:

F = (K ∙ Q) / (4.19 ∙ √ˉ N),

wherein:

• K– coefficient from 0.02 to 0.03;
• Q– boiler power in kW, indicated in the technical passport;
• N– chimney height in meters.

The result obtained must be checked for compliance with SNIP 2.04.05-91 and, if necessary, adjusted. The regulatory document states that, depending on the power, the internal cross-section of a round chimney should be:

It is possible to install square-shaped pipes if their parameters meet the requirements, but it should be taken into account that they tend to accumulate soot. Therefore, such products will have to be cleaned more often, otherwise reducing the hole will negatively affect the operation of the system. If two boilers are supposed to be connected to the chimney, the cross-section is calculated based on their total maximum power.

Determining the size of the chimney for an open type gas boiler

Unlike the previously mentioned units, such devices receive combustion air from the premises where they are located. To determine the transverse parameter, use two simple methods:

1. On the installed boiler, they are guided by the size of the pipe for removing combustion products. The cross-section of the chimney should be equal to it or slightly larger.
2. When there is no boiler yet, but its characteristics are known, or a chimney is installed for two heaters, its cross-section is determined by multiplying the power by 5.5. The result is obtained in cm 2. For calculations, the passport parameter is taken, not the thermal parameter, which can be an order of magnitude larger.

To calculate the diameter of the chimney, use the formula for the area of ​​a circle S = πr². Then r = √S/π. Substituting the previous result, you get the radius in cm. Multiplying by 2 and 10, you determine the diameter in mm. The calculated result is adjusted according to the table above.

Conclusion

Since human health and fire safety depend on the correct calculation of the chimney cross-section, it is better to overestimate the obtained result a little. Gas service workers usually turn a blind eye to this when issuing permission to operate a boiler. But if the cross-section is less than the standard, then a ban will be imposed, which means that all the work will have to be done again with associated costs.

To remove combustion products formed during the combustion of natural gas, chimneys of various designs are used. Previously, chimneys were built only from asbestos-cement pipes and bricks. Nowadays, a smoke exhaust pipe can be assembled from durable and lightweight materials that are much less expensive.

Requirements for chimneys for gas boilers

Design, assembly, installation and other activities aimed at installing a smoke duct are regulated by regulatory documents that clearly and clearly state the basic requirements for these structures.

Regulatory documents regulating the installation of chimneys for gas boilers include SNiP 2.04.05–91 “Heating, ventilation and air conditioning”, as well as DBN V.2.5–20–2001 “Internal gas supply arrangement”.

Based on these documents, the following requirements are imposed on smoke exhaust structures that will be used in conjunction with heating boilers:

The above requirements are general and must be met in all cases without exception. When installing a chimney, you should remember that even small deviations from the values ​​​​required by regulatory documents can cause a decrease in the service life of the chimney, and in some cases lead to more serious consequences.

Boiler structures and chimney outlet

Structurally, a gas boiler is a device consisting of a gas burner, to which gas is supplied through nozzles, and a heat exchanger, which is heated by the energy obtained during gas combustion. The gas burner is located in the combustion chamber. Heat movement occurs using a circular pump.

In addition, modern types of gas boilers are equipped with various self-diagnosis and automation modules, allowing the equipment to be used in autonomous mode. When choosing a chimney, pay attention to the type of boiler combustion chamber. The method of intake of air necessary for gas combustion, and as a result, the optimal type of chimney, will depend on its design.

The combustion chamber of gas boilers is of two types:

• open - provides natural traction. The air is taken from the room in which the heating equipment is installed. The removal of combustion products is carried out through natural draft using a chimney with an exit through the roof;
• closed - provides forced traction. Air intake for fuel combustion comes from the street. In rare cases, air can be taken from a special room equipped with forced ventilation. To simultaneously remove flue gases and intake fresh air, a coaxial type chimney is used, which is vented outside through the nearest load-bearing wall.

Knowing the type of combustion chamber, you can easily select or manufacture a chimney suitable for the design. In the first case, when the boiler is equipped with an open combustion chamber, a conventional thin-walled or insulated chimney is used.

For boilers with a closed combustion chamber, a coaxial chimney is used, which is a structure consisting of pipes of different diameters.

A pipe with a smaller cross-section is fixed inside a pipe of a larger diameter using special racks. Carbon dioxide and other combustion products are removed through the internal channel, and through the gap between the outer and inner pipes, fresh air enters the closed combustion chamber.

Methods for installing chimneys

• internal - chimneys made of metal, brick or ceramics. They are available in both single-wall and insulated double-wall constructions. Positioned vertically upward. There may be several elbows with a 30° offset;
• external - coaxial or sandwich chimneys. They are also located vertically upward, but the chimney is led out horizontally through the load-bearing wall. After the pipe has been removed, a 90° swivel elbow and support brackets are installed to allow installation in the desired direction.

When choosing a chimney installation method, you should take into account the size of the building in which the equipment is located. For small buildings, it is more advisable to use external chimneys, as they allow the chimney to be taken outside the room.

In other cases, you should build on your personal capabilities. If space allows and it is possible to provide high-quality insulation where the pipe passes through the ceilings, then an internal chimney will be the best solution. Especially if the structure is lined with brick or protected by a ceramic box.

Do-it-yourself chimneys for gas boilers

As with other heating equipment, a chimney for a gas boiler can be purchased in specialized stores. This will be a standard modular product, which is selected taking into account the type of boiler and its power.

What to make a chimney for a gas boiler from

A chimney for a gas boiler can be made from various materials. The main thing is that the material is non-flammable, resistant to chemically aggressive environments and does not allow gases to pass through the smoke duct.

Taking into account regulatory requirements, the following materials are used for the manufacture of the chimney:

• brick is a traditional material for the manufacture of chimneys for solid fuel stoves. For laying the chimney, class A or B stove fire-resistant bricks are used. When using gas equipment, a combined approach is often used, when a steel or asbestos-cement pipe is used as an internal channel;
• steel - used to create chimneys of any configuration. The quality and heat resistance of a material is determined by its alloy, which is indicated by a special marking. Thus, for the manufacture of chimneys, products made of AISI 316i, AISI 321 or AISI 310S steel are better suited;
• ceramics - a fired mixture of clay and sand, from which combined chimneys are made. The internal channel is made of a ceramic pipe of a certain cross-section. A box made of expanded clay concrete shell or brick is used as a protective casing.

If we carry out a detailed comparison, the best material in terms of price and quality ratio is galvanized steel AISI 321 and AISI 310S. Chimneys made of such steel are designed for flue gas temperatures up to 800 and 1000 o C, respectively.

The average service life of steel chimneys is 13–17 years, but due to the high standardization of parts, there is no need to completely change the design.

During repairs, only part of the burnt-out modules are replaced.

Ceramic chimneys have high performance characteristics and a service life of more than 50 years, but their cost is noticeably higher than their steel counterparts. Therefore, this type of chimney is recommended to be used only if there is a sufficient amount of funds and you want to build a structure for a long time. The use of brick chimneys in conjunction with gas equipment is unjustified both in terms of labor costs and the final cost of the structure.

How to calculate chimney parameters for a gas boiler

In order to correctly select or manufacture a chimney, it is necessary to calculate the cross-section of the chimney, as well as its height relative to the level of the ridge. The total height of the chimney is selected in accordance with the regulatory rules specified in SNiP 2.04.05–91.

Table: dependence of the chimney cross-section on the power of the gas boiler

• To calculate the pipe cross-section, the following formula is used - F = (K ∙ Q) / (4.19 ∙ √ˉ N), where:
• K is a constant value, the value of which varies from 0.02 to 0.03;
• Q is the maximum performance of gas equipment specified in the specification;

H is the estimated height of the chimney according to SNiP.

For gas boilers, the minimum height of the chimney must be at least 5 m. The height relative to the ridge is selected from the rules described at the beginning of the article. Let us remind you that the minimum height relative to the ridge must be at least 0.5 m.

After the pipe area has been calculated, it is necessary to compare the obtained value with the data shown in the table. If necessary, the calculated diameter of the smoke channel is rounded to a larger value.

To assemble the chimney, single-circuit steel pipes or special sandwich pipes of the required diameter are used. If the first option is chosen, then after assembling the chimney it is recommended to insulate it. In the second case, there is no need to insulate the chimney.

As an example, we will give the technology for installing a steel chimney for a gas boiler. To assemble the chimney, you will need straight steel pipes 50 or 100 cm long, 30° chimney outlets, a passage box for walls and ceilings, a deflector, crimp clamps and heat-resistant sealant.

If the diameter of the outlet pipe does not match the diameter of the chimney, then an appropriate adapter is used. It is better to use basalt wool as an insulating material.

Installation of a chimney for a gas boiler is carried out in the following sequence:

1. A single-wall or insulated pipe is connected to the outlet pipe of the gas boiler. To do this, the pipe is coated with a heat-resistant sealant, after which an adapter is put on it, which is tightened with a crimp clamp.
2. A similar approach is used to connect the adapter to the pipe. First, the mounting end of the adapter is treated with sealant. Next, a straight pipe is placed on it to the required depth. After which the connection is tightened with a clamp.

   
   Before assembling the chimney, it is recommended to check its completeness for the presence of all modules and fasteners

3. To bring the chimney through the ceiling, you will need to cut a square hole in it. The size of the hole is selected so that there is a distance of at least 20 cm from the chimney to the ceiling.
4. A steel box is mounted into a hole cut into the ceiling. For fastening, steel screws 30–50 mm long are used. Then a pipe is passed through the box, which is mounted on a module connected to the pipe. The space between the pipe and the box is filled with mineralized insulation. The top of the box is closed with a steel plate.

   
   The outlet of the chimney through the ceiling must be insulated with a steel box

5. If, after introducing the pipe into the inter-attic space, its displacement is required, then a 30° elbow is installed according to the scheme described above. In other cases, a straight section of pipe is installed.
6. To remove the chimney through the roof, similar actions are performed. First, a square hole of the required size is cut out. Next, a mounting plate with a hole for the pipe is installed. Then a straight section of the chimney is installed. Finally, a conical additional element made of steel or non-flammable plastic is put on the chimney.

   
   A deflector must be installed at the chimney outlet

7. At the final stage, the remaining section of the chimney is installed. A head and a deflector are installed at the end of the pipe. After assembly, the functionality of the assembled structure is checked. To do this, it is enough for the equipment to operate at 50–60% of maximum power for one hour.

When installing an external chimney, a 90° rotary elbow is used. The elbow is connected directly to the adapter, which is also mounted on the gas boiler pipe.

To remove the chimney, you will need to cut a hole in the load-bearing wall. The size of the hole is selected in the same way as in the case of the ceiling and roof. Next, a steel box is mounted in the wall through which the pipe is passed. Basalt or mineral wool is used to fill the box.

To re-rotate the pipe, another 90° elbow is installed. A special support with a bracket is used as a supporting structure, which is installed under the rotating elbow.

The installation step of the hanging brackets is 1–1.5 m. Further steps are similar - you need to assemble a chimney from straight products that are connected using clamps and sealant.

Do-it-yourself coaxial chimney for a gas boiler

• Before installing a coaxial chimney, you must check the completeness of the purchased product. If any of the elements is missing, then you should replace the missing set with a complete one, which should include:
• pipe with flange;
• coaxial elbow 90 o;
• connection adapter;
• wall trims;
• O-rings;
• connecting clamps;
• decorative rosette;

To assemble a coaxial chimney, you must have a complete set of pipes and connecting elements

The installation process of a coaxial chimney consists of the following steps:

Video: chimney for a gas boiler made of sandwich pipes

How to reduce the temperature of flue gases in a chimney

When natural gas is burned, carbon dioxide, steam, sulfurous salt-forming oxides, etc. are formed. The optimal temperature of the flue gases at the outlet of the chimney should be 100–110 o C.

If the temperature of the flue gases is below the dew point, that is, the condensation temperature of the air, then the water vapor contained in the combustion products will settle on the walls of the chimney. If this happens constantly, the chimney can quickly collapse.

In addition, the presence of constant condensation in the smoke channel leads to a weakening of natural draft. Therefore, it is so important to monitor the temperature of the flue gases, which directly depends on the cross-section of the chimney.

From the above we can conclude that with correct calculation, the temperature of the flue gases will be in the region of optimal values. If the temperature is too high and needs to be reduced, this directly indicates that the cross-section of the chimney does not correspond to the power of the gas boiler.

To reduce the temperature of the exhaust gases, it is recommended to reassemble the smoke exhaust system taking into account the standard values.

Video: condensation in the chimney

How to check and adjust the draft in the chimney of a gas boiler

Draft is a decrease in pressure in the place where fuel combustion occurs. The pressure decrease occurs due to the removal of combustion products through the smoke channel. Speaking within the framework of this article, draft forces fresh air into the combustion chamber, where there is a reduced pressure that occurs due to the fact that gas combustion products are discharged outside.

The speed of air flow in the chimney can be measured with a special device - an anemometer

• The following methods are used to check the draft level:
• visual inspection - there should be no smoke in the room where the heating equipment is located;
• measurement with a special device - an anemometer. It is used to control air speed.

To control traction, it is better to use the latter method, since only it will show the exact value. When measuring natural draft, the flue gas velocity should be in the range of 6–10 m/s. The value is taken from SP 41–104–2000 “Design of autonomous heat supply sources.”

If it is necessary to reduce the draft level, then this will require reassembling the chimney based on a chimney of a larger cross-section. To increase traction, it is recommended to check the quality of the installation joints and mechanically clean the smoke channel using a steel cable with a brush attachment.

If this does not help, then the only way out is to replace the chimney with a preliminary calculation of the chimney cross-section. In this case, it is desirable to reduce the number of rotating elements to a minimum or remove them altogether.

Why does the boiler blow out and how to fix it

The main reason why the burner in a boiler blows out is the backdraft effect that occurs due to problems with the chimney.

Before starting any measures, you should check the height of the chimney above the ridge level and the presence of an installed deflector, which reduces the penetration of wind flows into the chimney.

Sometimes, in order to increase draft, you need to clear the chimney of soot

1. In order to solve the problem with the boiler blowing out, you will need to do the following:
2. First of all, you need to check the draft level in the pipe. It is better to use an anemometer. If you cannot find it, then with the boiler running you need to lean the paper against the outlet of the chimney. If the sheet is attracted to the chimney, then there should be no problems with draft.
3. If you find that the blowing occurs due to a loss of natural draft, you will need to check the chimney joints. A thermal imager is used for this. If the pipe allows air to pass through, the device will show a strong temperature difference between the main pipe and the junction of the two modules.
4. After completing these simple steps, you will need to check the traction level again. If natural draft has not improved, then it is necessary to carry out work to correct the height of the chimney and install a deflector. During installation, heat-resistant sealant and crimp clamps are used.

In cases where the work described above does not produce results, you should contact the gas service to check the gas equipment. Perhaps the problems with blowing are associated with hypersensitive automation.

Video: how to check draft in a gas boiler

Compliance with regulatory requirements is a guarantee that no emergency situations will arise during the operation of the chimney. This is especially true for vertical chimneys, when correcting errors made during their installation will require spending a lot of time.