How To Make A Coaxial Chimney With Your Own Hands: Installation Requirements, Installation, Operation, Etc

2024 Author: Bailey Albertson | [email protected]. Last modified: 2023-12-17 12:53

Do-it-yourself coaxial chimney: types, design requirements, installation and operation

Heating equipment operating on solid or liquid fuels requires a complete system for the removal of combustion products. Previously, a classic chimney made of single-wall steel pipes was used as a discharge device, which has a lot of disadvantages. More practical and efficient coaxial pipe solutions are now being used.

Content

• 1 What is a coaxial chimney

  • 1.1 The principle of operation of a coaxial chimney
  • 1.2 Advantages and disadvantages of the coaxial chimney design

• 2 Types of coaxial chimneys

  2.1 Video: coaxial pipe for parapet gas boilers

• 3 Basic elements of the chimney

• 4 Making a coaxial chimney with your own hands

  • 4.1 Calculation of chimney parameters

    4.1.1 Table: dependence of the cross-section of the flue duct on the rated power of the heating device

  • 4.2 Required tools for the installation of a coaxial flue
  • 4.3 Preparatory work before installing the chimney

  • 4.4 Step by step instructions for installing a coaxial chimney

    4.4.1 Video: coaxial chimney in a private house

• 5 Chimney insulation

  5.1 Video: removing condensate on the air supply pipe in winter

• 6 Cleaning and periodic repairs of the chimney

What is a coaxial chimney

The term "coaxial" is used to designate any structure consisting of two objects located around a common axis. In the case of a coaxial chimney, this is a flue duct consisting of pipes of different sections.

The distance between the pipes is the same along the entire length of the chimney, including bends, bends and other elements. This is achieved through special bridges, which are located along the entire length of the chimney.

The coaxial chimney is made of two pipes with a common central axis, separated by special internal bridges

The principle of the coaxial chimney

The duct between the inner and outer tubes provides a constant supply of fresh air, which is necessary to maintain the combustion processes. The inner pipe is a channel for the removal of flue gases and other combustion products. In fact, the special design of the coaxial pipe allows the chimney to perform two functions at once: removal of harmful substances and supply ventilation.

Through the inner channel, flue gases are removed, and fresh air enters the combustion chamber through the annular space

The main area of application of coaxial chimneys is wall and floor gas boilers with a closed combustion chamber, gas water heaters and convectors. Coaxial chimneys are not used with solid fuel equipment.

Advantages and disadvantages of the coaxial chimney design

Among the advantages of coaxial chimneys are:

1. Versatility. The installation of the coaxial pipe is carried out by means of its output through the load-bearing wall, ceiling or roof ceilings. Depending on your needs, you can select the required chimney dimensions.

   

   A coaxial chimney can be brought out in the traditional way through ceilings and roofs, but it is much easier to do this through a load-bearing wall if a boiler with a closed combustion chamber is used

2. Environmental friendliness. The higher the efficiency of heating equipment, the better the fuel burns. This, in turn, reduces the concentration of harmful substances and gas released into the atmosphere.
3. Increased efficiency. Due to natural heat exchange with the inner pipe, heated air enters the combustion chamber, which significantly increases the efficiency of heating equipment. At the same time, fuel consumption becomes noticeably lower.
4. Safety. Cold air entering through the outer pipe cools the combustion products discharged through the inner channel. The risk of fire and burnout of the chimney is minimized.
5. Easy to install. The chimney assembly does not require special tools or special skills in construction. The chimney design allows you to quickly install and commission any equipment with a closed combustion chamber.

Despite its many advantages, the design of the coaxial pipe is not without its drawbacks. At temperatures below -15 ^of coaxial chimney can greatly obmorznut.

This is due to the fact that, in fact, is the advantage of the design in question - cold air is heated due to the temperature of the flue gases leaving outside. Combustion products are strongly cooled and can condense at the outlet of the chimney, which leads to severe icing on the chimney head.

One of the main advantages of a coaxial chimney turns out to be its main disadvantage - at low temperatures outside, condensation of combustion products occurs and ice freezes on the head of the pipe

To prevent icing, you should choose special devices designed to work at negative temperatures, as well as more carefully calculate the section of the chimney.

Types of coaxial chimneys

Depending on the method of laying the chimney, coaxial-type chimneys are divided into two types:

1. Vertical - the chimney is located strictly in a vertical position. Gases and combustion products rise from the fuel chamber and are released into the atmosphere above the ridge level. Mainly vertical structures are used in residential buildings and provide a good level of natural draft.
2. Horizontal - the main duct of the chimney is represented by a structure located in a horizontal position, which is led out through the load-bearing wall. In this case, the flue gases escape to the outside in the immediate vicinity of the heating equipment. It is more often used in private houses where closed-type heating systems are installed.

A vertically oriented coaxial chimney, despite some advantages, is a more expensive and difficult system to install. The total length of the flue duct usually exceeds 5 meters, which greatly complicates the process of installation and fixing of the structure.

For the manufacture of a coaxial type chimney, various grades of steel and plastic are used. In accordance with this, several types of chimneys can be distinguished:

• galvanized - the most affordable option for a coaxial chimney. The average service life of the product does not exceed 5–7 years, after which the structure partially rusts or is damaged. The cost of the product depends on the manufacturer and technical parameters, but rarely exceeds 2–2.5 thousand rubles;

• made of plastic and aluminum - a combined option for private use. The inner channel of the chimney is made of aluminum up to 2 mm thick. The outer tube is made of high-strength heat-resistant polypropylene. Such chimneys are used only in the private sector to work together with boilers of small and medium power;

  

  Galvanized steel coaxial chimneys are designed for 5-7 years, plastic products will last much longer

• stainless - more reliable and durable chimneys than galvanized ones. They are designed for 10-12 years of use. The cost is almost the same as stainless steel products. In industry and collective systems, chimneys are not used, since "stainless steel" does not withstand a high concentration of chemicals;

• made of high-alloy steel - the strongest and most durable version of the coaxial chimney. High alloy steel is resistant to high temperatures and chemicals in flue gases. Average service life is at least 15 years.

  

  A coaxial chimney made of high-alloy steel, unlike "stainless steel", does not deteriorate under the influence of aggressive chemicals contained in combustion products and lasts at least 15 years

In the line of some manufacturers (Electrolux, Viessmann, Schiedel) there are models of coaxial chimneys with an additional thermal insulation layer. This is a classic design with two channels, which is located in another pipe. The voids between the outer pipes are filled with non-combustible heat-insulating material that prevents freezing and blockage of the air channel.

Video: coaxial pipe for parapet gas boilers

The main elements of the chimney

A coaxial chimney consists of various elements that make it possible to manufacture a chimney of the desired configuration for specific operating conditions and structural features.

The coaxial chimney kit contains everything you need to install it

A ready-made coaxial chimney kit from the manufacturer includes the following elements:

• pipe - a straight piece of pipe to form a chimney;
• elbow - an element for changing the direction of the pipe by 45 or 90 ^o;
• coupling - a device for connecting two straight sections of the chimney;
• condensate collector - a device for collecting and removing moisture flowing down the pipes. Used in vertically oriented systems. To maintain constant pressure inside the combustion chamber, it is equipped with a special shutter;

• revision - a separate section of the chimney used to inspect and clean the chimney;

  

  The assortment of the leading manufacturers of coaxial chimneys contains more than 80 items of various connecting, fastening and functional elements

• adapter - a vertical or angular (90 ^°) element connecting the chimney and the boiler pipe;
• nozzles - pipe sections that are put on the smoke and air duct. They are used to delimit the area of air intake and the place of emission of combustion products;
• seal - a special element mounted at the place where the pipe passes through ceilings, roofs or walls;
• fasteners - flanges, wall brackets and clamps.

To ensure the tightness of all connected parts of the structure, special sealing rings made of heat-resistant material (thermoplastic) are used. When heated to a high temperature, the ring expands and changes into a more elastic shape, which allows it to maintain its tightness even at high pressure.

Making a coaxial chimney with your own hands

In order for the chimney to cope with its tasks throughout its entire service life, it must be correctly calculated and correctly assembled.

Calculation of chimney parameters

When designing a chimney, special attention should be paid to calculation operations, since the performance of the system as a whole will depend on the parameters of the chimney. The cross-sectional area of the exhaust duct of the coaxial chimney should not be less than the cross-section of the connecting pipe of the heating equipment.

The cross-section of the smoke channel of the coaxial chimney is selected for the dimensions of the heating equipment branch

In collective systems, when connected to two or more heating devices, the channel cross-section increases in proportion to the size of their branch pipes. This is necessary in order to ensure sufficient throughput of the flue gas duct when several boilers are operating simultaneously.

Table: dependence of the cross section of the flue duct on the rated power of the heating device

Internal channel section, mm	Rated power of equipment, kW
120	24
130	25-30
170	40–45
190	fifty
230	80–90

The cross-sectional diameter of the outlet is calculated by the formula - F = (K * Q) / (4.19 * √Н), where:

• K - constant coefficient equal to 0.02–0.03;
• Q (kJ / h) is the maximum power of the gas boiler specified in the device specification;
• H (m) - design height of the smoke channel.

For example, let's calculate the cross-section of the chimney outlet for the Ariston CLAS B gas boiler. The maximum heat output in heating mode is 24.2 kW. The height of the smoke channel is 8 m.

1. To convert the power from W to kJ / h, we will use any of the online programs that are easy to find on the Internet. We get that Q = 87 120 kJ / h.
2. We find the cross-sectional area using the above formula: F = (0.02 * 87 120) / (4.19 * √ˉ8) = 147.03 mm.

After calculations, the resulting value must be compared with the data in the table. It indicates the optimal cross-sectional area of circular chimneys for domestic gas boilers. If necessary, the value is adjusted up or down. In our case, you can use a pipe with a diameter of 130 mm.

Necessary tool for installing a coaxial flue

To install a ready-made coaxial chimney kit you will need:

• puncher;
• electric drill;

• crown nozzle for wood / concrete;

  

  Using a hammer drill and a crown nozzle, you can drill a hole in a log, timber or concrete wall

• screwdriver;
• Phillips and slotted screwdrivers;
• heat-resistant sealant;
• goggles, gloves and overalls.

For self-manufacture of a coaxial chimney, you will need two pipes of a suitable diameter, which are connected using stainless steel jumpers. For connection, steel rivets or self-tapping screws are used.

It is important to understand that it will not be possible to completely repeat the design of finished industrial chimneys. You can only make a straight section of a coaxial pipe yourself.

Preparatory work before installing the chimney

According to statistics, coaxial chimneys are the safest. The rules for their assembly and installation are described in detail in SNiP 2.04.08–87, SNiP 2.04.08–87 and PB 12–368–00. Before installing the chimney, you should carefully study the attached instructions and familiarize yourself with the requirements specified by the manufacturer of the structure.

In general, when installing a coaxial chimney, the following rules must be observed:

1. The horizontal section of the chimney passing through the load-bearing wall must be inclined by 3 ^o. Such a slope is needed for the free drainage of moisture that forms on the walls of the air channel.

   

   The horizontal section of the chimney should be installed with an inclination of 3 degrees away from the boiler to ensure natural drainage of condensate

2. The maximum length of the flue duct of a standard coaxial pipe should not exceed 5 m. With an increase in the length of the flue, the cross section of the inner flue also increases.

3. The minimum distance from the outlet of the chimney to the nearest building should be equal to:

   • if a deflector is installed at the end of the pipe - 5 m;
   • if there are no windows and doors on the adjacent wall - 2 m;
   • in all other cases - 6 m.
4. The length of the outer part of the chimney must be at least 0.2 m. Otherwise, at subzero temperatures, severe icing of the air channel is possible.
5. When installing a coaxial chimney in regions with a strong gusty wind, a special damper is mounted at the end of the outer part. In this case, the distance from the air channel to the outlet should not be less than 0.35 m.

When installing a coaxial chimney in wooden houses, the junction of the pipe with the bearing wall or ceiling is sheathed with non-combustible material. Usually an asbestos pipe or a box made of asbestos-cement slabs is used.

Step-by-step instructions for installing a coaxial chimney

Before installing the chimney, you should carefully check the completeness of the purchased device. If any parts are missing, then the chimney assembly must be postponed. In addition, it is imperative to check the diameter of the outlet pipe and the section of the inner channel.

Coaxial chimney assembly technology consists of the following stages:

1. In the designated place, markings are made for the outlet of the smoke channel to the street. For a floor-standing gas boiler, the chimney outlet must be located 1.5 m above the combustion chamber. For wall-mounted, it is allowed to withdraw the pipe immediately after mounting the swivel elbow.

   

   The chimney of a wall-mounted boiler can be removed immediately after installing the rotary elbow on its branch pipe

2. After applying the layout using the punch with the castellated nozzle is drilled hole of the desired diameter at an angle of 3 ^on the surface of the wall. It must be borne in mind that in addition to the pipe, an insulating gasket is installed in the hole.

3. By gas boiler outlet nozzle adapter is connected, which is mounted on the straight pipe portion coaxial or knee 90 ^on. To connect the elements, a crimp clamp is used, which is tightened with a Phillips screwdriver.

   

   A special adapter is used to connect the chimney to a gas boiler

4. An asbestos pipe and a sealing collar are installed in the wall hole. Further, the straight section of the chimney is led out. From the inside, the pipe is connected to a swivel elbow or extension nozzle and is fixed with a compression clamp.

5. The hole in the wall is additionally insulated with special overlays. For this, the place of contact is treated with a heat-resistant sealant, and the nozzle is screwed onto galvanized self-tapping screws. If necessary, a deflector or blowout protection is put on the end of the pipe.

   

   The deflector protects the boiler from blowing out through the chimney

When installing a vertical structure, a hole in the ceiling is cut out using a grinder with a disc for wood. At the junction, a box of asbestos-cement slabs is mounted. In this case, the distance from the outer pipe to the ceiling should not be less than 20 cm.

A similar condition is met when the pipe exits through the roof. For this, a special pass-through is mounted at the interface, which is attached directly to the roofing material using galvanized self-tapping screws.

Video: coaxial chimney in a private house

Chimney insulation

Freezing and icing of the head of the coaxial chimney is associated with the ingress of condensate into the air intake duct. To prevent moisture ingress, check the slope of the coaxial pipe relative to the combustion chamber. If the slope angle is at least 3 ^o, then the freezing of the head will occur only at temperatures below -15 ^o C.

The main mistakes during the installation of the chimney are associated with the incorrect inclination of the horizontal sections

Additionally, a special element can be installed on the head, which lengthens the inner channel by 10–40 cm relative to a larger diameter pipe. In addition, several holes can be drilled at the bottom of the outer tube. This will allow air intake even with partial freezing of the head.

If the slope is insufficient, the frosting cannot be eliminated, since the condensate will not drain towards the combustion chamber, but, on the contrary, towards the outlet, which will lead to the formation of icing and icicles at the end of the pipe. Warming by lining with heat-insulating material from the outside of the pipe will not help.

Video: we remove condensate on the air supply pipe in winter

Chimney cleaning and periodic repair

For the operation of heating equipment with a closed combustion chamber, natural gas is used - methane. In the process of gas combustion, harmful aromatic hydrocarbons, toluene, benzene, etc. are formed. The formation of soot and burning does not occur as such.

In case of a sharp loss of draft, it is recommended to contact a specialist to inspect the chimney for damage. To do this, high-precision thermal imagers are used to detect burnout or breakdown in the chimney structure.

A highly sensitive thermal imager is used for inspection and revision of the chimney

To repair the chimney, it will be necessary to dismantle all the elements of the chimney duct up to the damaged area. After replacement, the structure is assembled taking into account regulatory requirements.

A coaxial chimney is a highly efficient and practical design that significantly increases the efficiency of heating equipment. Subject to the rules described in the regulatory documents, the coaxial chimney does not require periodic repairs and reliably removes all flue gases.