Chimney For The Gas Boiler: Standards And Requirements For Installation, A Comparative Overview Of Species

If you choose to heat your house with gas, you must take care of the flue gas venting. This means that it is necessary to choose and properly install a chimney for the gas boiler. Compliance with the rules and regulations in this matter cannot be categorically neglected, because it can put not only the health but also the lives of the occupants of the house in question.

We are ready to share with you useful information about the rules of installation and connection of the flue pipe for a gas unit, about the specifics of selecting the optimal design. The information is complemented by clear illustrations and video instructions.

Article content:

  • Why a chimney at all?
  • Selection of materials for chimney construction
    • Stainless steel chimneys
    • Ceramic chimneys
    • Coaxial chimney
    • Brick chimney
    • Asbestos cement chimneys pipes
  • The subtleties of chimney design
    • Rule #1 - observing duct cross-sectional standards
    • Rule #2 - providing condensate control
    • Rule #3 - choosing the shape of the sectional  construction
    • Rule #4 - making slopes, curves, ledges
    • Rule #5 - correct pipe connection
    • Rule #6 - subtleties of pipe location on the roof
    • Rule #7  -  -  Compliance with fire safety rules
  • Chimney selection depending on boiler type
    • Chimney for a boiler with open burner
    • Chimneys for turbine boilers
    • Chimney arrangement details for two boilers
  • Preliminary chimney calculations
  • Chimney installation options
    • Interior chimney
    • Exterior construction
    • Installation of coaxial chimney
  • How to rework an old chimney?
  • Conclusions and useful video on the subject

Why do you need a chimney at all?

One of the most dangerous products produced by almost all types of combustion is carbon monoxide. It is an insidious and very dangerous substance, the inhalation of which threatens severe forms of poisoning.

When a gas boiler burns fuel, carbon monoxide is produced during combustion among other combustion products.

If the flue that drains the products of combustion is not installed correctly or is damaged, it can lead to poisoning.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

This diagram shows the chimney for the gas boiler and reflects its location inside the building or outside

The dangers should not be underestimated. Carbon monoxide is colorless and odorless, so poisoning can go unnoticed in a house.

In the human body, carbon monoxide molecules interact with hemoglobin. This creates what is called carboxyhemoglobin, which prevents oxygen molecules from reaching human tissues.

Besides that, carbon monoxide can also affect other biochemical processes in the body very badly. There have been cases where carbon monoxide poisoning has been discovered too late and the person simply could not be saved.

To avoid such problems, it is recommended to pay the closest attention to the proper design and installation of the chimney, as well as its further maintenance.

Gallery of images

Photo of

Gas chimney

Certified chimney structures and elements

Metal chimney structures

An external diagram of the chimney structure

Laying coaxial flue in the boiler room

Connection of the flue to the collective ducts

Tight flue connection

Gas alarms

Supplying materials for flue construction

Gases The gases discharged through the chimney of a boiler fuelled with this fuel have a low temperature of about 150⁰, therefore the requirements to the material of the chimney are somewhat different.

When it burns, steam is produced with an admixture of carbon dioxide - substances neutral and not contributing to the emergence of destructive processes, but, besides them, in the combustion products there is also aggressive sulfuric acid.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The type of chimney depends on where the heating system is installed. When installing a gas boiler in a newly built house, the chimney is part of the project. Installing a boiler in an old house, you will have to reconstruct some things

When installing gas heating of a country house and a chimney for a gas boiler, only very durable materials resistant to many external factors should be used. They must be fire-resistant, capable of contact with moisture and acids released during combustion of gas and deposited on the walls of the chimney in the form of condensate.

When choosing a material, you must pay attention to such a parameter as the gas permeability of the material. It must be zero. In addition the material must not be too heavy as such a construction puts additional stress on the walls and foundation of the house.

Homeowners are increasingly choosing light pipes made of acid-resistant stainless steel, use furanflex, protective sleeves, ceramic modules.

Image gallery

Photo of

The outside of a gas boiler chimney

The inside of the chimney

Polymerized black steel pipes

Brick chimney with steel sleeve

Ceramic chimney

Ceramic chimney

Assisted cement chimney

Sandwich pipe pipe for gas boilers

Stainless steel chimneys

These designs are considered the best choice. They are exceptionally resistant to many types of corrosive influences, have a relatively low weight and provide excellent draft. The service life of a steel chimney is usually about 15 years.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The light weight of a stainless steel chimney construction allows for installation by yourself. Moreover, the installation of such a chimney is not too difficult, since the individual elements of the structure are sold in the form of ready-made modules

Galvanized steel with the removal of combustion products copes much worse than stainless steel. Moist and hot fumes with high acidity quickly destroy this material. The galvanized chimney will have to be replaced after 5 years.

Ceramic chimneys

They have an exceptionally high service life - they can last up to 30 years. Especially popular and convenient are the European-made models with a steel outer contour.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The technical term \"ceramic chimney\" is the definition of a three-layer system whose outer part is made of ceramicite concrete shell, the inner one is a ceramic channel. Between the shell and the duct there is mineral wool insulation

But this option also has a number of serious drawbacks:

  1. High construction weight, which must be correlated with the load-bearing capacity of the foundation and walls of the house.
  2. High installation requirements. It is believed that in order to obtain maximum draft a ceramic chimney must be located strictly vertically, and this configuration is not convenient everywhere.

Coaxial chimney

Coaxial chimney is a highly efficient, modern, but expensive choice. The design of such a chimney is two pipes nested inside each other. The inner pipe drains the combustion products, while the outer pipe is designed to bring in air.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The coaxial chimney installation diagram in the horizontal version. This design is versatile. It is made up of several parts nested one inside the other. The individual elements are held together due to the presence of special crosspieces

The coaxial chimney is also delivered in the form of modules, which facilitates its assembly and installation. Another advantage is the increased level of safety. This is, of course, if the coaxial chimney installation standards and building regulations were followed during installation.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Coaxial chimney structures are highly efficient, safe and relatively easy to install. They are suitable for draining the combustion products of gas heating units

Brick chimney

This is not the best option for a gas boiler. Massive construction usually does not have a good draft, weighs too much and does not last long. This kind of chimney must be cleaned often, a lot of condensate accumulates on its surface, so its service life when used with gas equipment is short.

Brick chimney is also dangerous because due to the unevenness of the internal walls at low outside temperatures the back draft effect can appear or a water plug can form, leading to the termination of the combustion process.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

When equipping a brick chimney it is recommended to perform its liner: a special steel liner-guille is inserted inside the brickwork body, its smooth walls contribute to the removal of combustion products and prevent accumulation of deposits

But if the house already has an old brick chimney, it may well be used. A special stainless steel insert is inserted inside the structure, and the brickwork becomes a protective case. Of course, the diameter of the insert and its configuration must meet the standards described above.

Chimneys made of asbestos cement pipes

Such structures are quite rare. They are superseded by more efficient materials. If you buy a relatively inexpensive asbestos-cement pipe, its installation is complicated by the fact that it has a large mass and must occupy a strictly vertical position.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Material is hygroscopic and absorbs condensate that appears at the output of heated gases. Overheating can result in an explosion or a fire

In view of its disadvantages, this option is not strictly recommended. It is budget-friendly, of course, but can your health be measured in money? Lifetime asbestos cement chimney is not more than five years.

All variants of chimneys for gas equipment is recommended to equip draft enhancers.

The subtleties of flue design

When designing a chimney, everything matters: its size, configuration, cross-section, slope and other parameters. When constructing a chimney from a gas boiler, it is necessary to strictly adhere to the requirements of regulatory documents: SNiP 2.04.05-91 and DBN B.2 .5-20-2001.

Rule #1 - observance of channel cross-section standards

The cross-sectional area of the flue duct must be not less than the cross-section of the gas boiler spigot by which the device is connected to the chimney.

Canal constrictions, curvatures and the use of unsuitable cross-sectional modules are not permitted in the construction and connection of flues for gas boilers throughout their entire length. That is, the cross-sectional area of the duct should be equal to the total size of the spigots of both units.

Rule #2 - Ensuring condensate control

Modern gas boilers are designed so that the maximum amount of heat is delivered to the heat exchanger. This high efficiency promotes combustion products with relatively low temperatures.

As a result, moisture forms on the walls of the chimney. An increased amount of condensate, which includes aggressive substances, can have a destructive effect on the integrity of chimney walls.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

To connect the gas boiler to the chimney structure use a special tee, on which a condensate collection device is mounted

In the bottom of the flue must be present condensate collector in the form of a removable container made of plastic or stainless steel. Not prohibited for use and the glass of galvanized steel, but it will have to change frequently.

In order to protect the structure is recommended not only to lay a chimney of bricks, but also to perform its sleeving, ie, insert a special tube of stainless steel inside. Such pipes are durable and well resist corrosion.

An alternative solution to combat condensation can be lining, i.e. installation of a special flexible chimney. A special container is used to collect the condensate. It is installed just below the place where the boiler spigot connects to the chimney.

Rule #3 - choice of sectional shape design

The traditional cylindrical shape of the chimney is considered optimal for efficient removal of combustion products. In addition, it is easier to perform preventive cleaning in such a chimney.

Fairly acceptable, though not as convenient, are chimneys with an oval cross-section. Square designs also have the right to exist, but the draft indicators in them are usually reduced.

Rule #4 - making slopes, turns, ledges

A vertical chimney without ledges is considered optimal for the floor gas boiler. In practice, it is not always possible to achieve such an arrangement.

Deviation from the vertical is allowed not more than 30 degrees. In this case, you should make sure that the size of the cross-section of the sloping section meets regulatory requirements.

Therewith the pipe itself, connecting the chimney and the boiler, should include a strictly vertical section of height of half a meter or more. Of course, some sections of the chimney may be made horizontal if necessary, but there must not be too many of them.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

When installing a chimney structure for a gas boiler, sloping sections are permitted, the slope must be 60° or more degrees relative to the horizontal, the length of the sloping section up to 1 m

Even if the room in which the flue is installed is about three meters high, then the total length of horizontal segments of the flue must not exceed these dimensions.

Although, as mentioned earlier, the closer the chimney design is to the vertical, the better. It is not allowed that the slope of the chimney towards the boiler is more than 0,1 degree. As for the turns of the chimney structure, their maximum number is three turns, not more.

Rule #5 - correct connection of pipes

To connect the individual parts of the chimney structure use special clamps. The slope of the chimney construction elbow may be 15-90 degrees. A certain distance must be kept between the connecting pipes and the rest of the surfaces.

It depends on what materials these surfaces are covered. In places where combustible or even combustible materials are used, it is recommended to maintain a distance of at least 25 cm.

The distance from the surfaces covered with flammable materials should be at least 5-10 cm. To protect the chimney from flammable materials use asbestos board, brickwork, etc.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

When installing the chimney for the gas boiler all its elements must be securely fixed, maintaining the correct step between the fixings

Special attention should be paid to the joints of the individual segments of the chimney construction. They must be made of durable materials that do not sag when exposed to external influences.

The same characteristics should have all elements of the chimney mountings. Horizontal or inclined sections of the chimney should not be under load.

The elements of the chimney are inserted into each other to a depth that is equal to half the diameter of the pipe or exceeds this figure. No gaps in these places are not allowed, the connection must be tight and airtight.

In case of violation of the tightness of the connection of individual elements of the chimney, carbon monoxide can penetrate unnoticed into the room. Therefore, the condition of the chimney should be checked periodically, and good ventilation should be arranged in all rooms where chimneys are laid.

Rule #6 - subtleties of positioning the chimney on the roof

Chimney pipes should be 50 cm or more above the roof ridge, with the distance from the parapet edge to the chimney should be no more than 150 cm. If the axis of the chimney is located 1-1.5 m from the roof ridge, it shall be 50 cm or more above the level of the ridge.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

This diagram clearly shows how to determine the height of the chimney in relation to the roof ridge according to the technical regulations, so that it does not obstruct the draft

If the pipe is further away from the ridge, it can be made the same height as the ridge. The chimney can be even lower if it is separated from the roof ridge by a distance of more than three meters.

In this case it is necessary to draw a conditional line down from the ridge at an angle of 10 degrees to the horizon. The height of the chimney should reach this mark. It turns out that the further the chimney is from the ridge, the lower should be its height relative to the roof ridge.

On a flat roof there is no chimney, so here a 100 cm high chimney is erected according to the regulations. On a combined roof the height of the chimney pipe must be about two metres.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The chimney section located above the roof and within the unheated attic must be insulated to improve the draught and prevent condensation. One option for such insulation is a basalt shell

The outside of the chimney should necessarily be insulated. If this is neglected, condensation will accumulate on its surface. Moisture can penetrate into the chimney, leading to the development of corrosion processes and damage to the structure.

The part of the chimney structure that is located on the outside of the house also needs to be insulated. Insufficient insulation can also reduce the efficiency of the chimney, reducing its draft.

If it is not possible to bring the chimney through the upper ceiling and roof, coaxial chimneys are used. This option can be led through the wall, with the intensity of the removal of combustion products of the blue fuel is not reduced in any way.

Rule #7 - Compliance with fire safety

Fire safety requirements must be considered during the installation phase of the chimney. When passing the duct through walls of different materials, they are different:

  • if the wall is made of wood, insulation of fire-resistant material is needed around it, and the pipe itself should be wrapped in asbestos;
  • in a brick, concrete wall, insulation of installation foam is sufficient.

The chimney design must comply with the requirements set forth in the instructions enclosed with the boiler.

The chimneys of gas-to-heat boilers are predominantly of the overhead design type. According to the overhead design, the duct is installed directly on the floor slab of the heating unit. However, it is permissible to connect to wall chimneys by means of no more than 40 cm long pipes.

In case of connection to a wall chimney, a gap of 14 cm must be left between the bottom line of the pipe and the floor slab to be combusted. A gap of 50 cm must be left between the upper line of the spigot and the combustible ceiling if there is no fire protection, and 40 cm if there is protection.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The passage of the flue through the combustible structure shall be provided with non-combustible thermal insulation material or a sandbox-type device

The area where the flue crosses the combustible ceiling shall be provided with a sand box or a seal of a non-combustible insulating material.

Chimney selection according to boiler type

Gas boilers are equipped with one of two types of combustion chambers: open or closed. Externally the heating units do not differ in any way, but the principle of operation is different. Chimney design is chosen depending on the type of combustion chamber.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Manufacturers supply many models of gas boilers to the market. When choosing a unit to heat your home, you need to decide in advance what is more suitable for your particular home - an open or closed type burner. Ignorance of these subtleties can create problems during operation

The location of the chimney must also be determined in advance. It can be internal or external. The projects of new houses usually provide for the installation of internal chimneys. When gas heating is transferred to old buildings, a remote chimney is installed.

Smoke for a boiler with an open burner

The simplest arrangement is an open chamber. It consists of the burner itself and a coil underneath it. The latter consists of thin tubes through which the coolant circulates. The device works only when there is air, so the burner is called atmospheric.

Air such a boiler receives from the room where it is installed, although there are models that are mounted on the wall and make an air intake hole in it.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The wall boiler is quiet during operation. The parts included in its construction are practically not subject to wear and tear. The maintenance is very simple - check the ignition, but as for the fuel consumption, these boilers cannot be called economical

For a good operation of an open chamber boiler, a pipe going outside and an excellent draft resulting from the movement of air through the chimney are required. The unit is well suited when you want to heat a large area house located outside the city limits.

There are 2 solutions:

  1. Maximum straight pipe, located horizontally, is carried through the wall, and outside direct it up along the wall to the desired height. This version of the chimney is called an outside chimney.
  2. From the boiler, the pipe is pulled upward. It shall pass through the floors and extend above the surface of the roof. In such a chimney it is permissible to make two 45⁰ bends.

The first variant is easier to perform, but a quality insulation is required. This will reduce the amount of condensation but will get rid of it completely. At the outlet a condensate collector and a T-piece are indispensable.

The second variant is complicated by the fact that the flue passes through the ceiling and the roof pie. Therefore, in these places, in accordance with the fire safety requirements, the installation of ceiling-through-units is required.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Factory-through-unit. It is installed with prior insulation made of foil-coated basalt wool capable of withstanding temperatures above 150⁰. If this requirement is neglected, the material will sinter and lose its insulating properties

There are such terms as mounting the chimney \"by smoke\" and \"by condensate\". Assembly of the first method is carried out at the arrangement of the internal chimney, and the second - when building an outdoor chimney

In the first case, already installed the lower element is inserted into the upper, which prevents the seepage of gases into the room. In the second - do the opposite.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Collecting the chimney \"by condensation\" will not allow moisture to penetrate the insulation layer, therefore, prevent corrosion of the pipe. Masters of furnace business advises to collect the chimney on the 3 - combined option: \"on the smoke\" horizontal sections, and \"by condensation\" those that pass through the attic or the second floor rooms that are not heated

If the pipe is taken out to the 2nd floor living, it must bring in an aesthetic appearance. For this purpose, special screens are used, which are screwed to the floor. When the chimney goes to the attic, no additional work is required.

Chimneys for turbine boilers

Boilers with a blowing burner are called turbine boilers. This is a more advanced design with forced oxygen injection and a closed chamber with a nozzle located in it. The air is supplied by an externally mounted fan through a special duct.

The heating unit has double walls with water in between. The liquid is heated when the gas burns, and the combustion products are displaced by the blower into the chimney.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

In the classical sense there is no chimney as such - the pipe is simply led outside, although some place it in an atmospheric chimney

A coaxial chimney fits the turbine boiler. One of its pipes removes exhaust gases at a distance of up to 3 m, while the other pipe is used for the inflow of air necessary for the combustion process.

In terms of ecology, such a unit is safer, the combustion process is controlled by the automation for gas boilers. The fuel in it burns up to almost 100%. The efficiency is greater because the water is in contact with the walls of the chamber.

The use of horizontal short flues is possible. As a result of using a double chimney, the air coming from the street is heated by the exhaust gases.

Special arrangement of the chimney for two boilers

Each device using gas as fuel must have an individual chimney. In case of urgent need, as an exception, the connection of 2 units, simultaneously operating, gas-consuming equipment is allowed. The main condition is to maintain a distance of at least 0,7 m between the points of pipe connection to the chimney.

If the house has not only a gas boiler but also other heating or water heating appliances, the following regulations should be observed:

  1. No more than two such appliances may be connected to one chimney located on the same or on different floors.
  2. The flue gas discharge openings for these devices must be at different levels.
  3. The flue inlets must be separated by a distance of 50 cm or more.
  4. The flue gas entry from two devices on one level is only allowed if there is a special flue breaker insert inside the flue.
  5. The height of parallel flue inlets equipped with a breaker must be at least one meter.

Course, the erection of several chimneys will cost more than just one construction, but you should not disregard the requirements of building regulations and safety rules for the sake of dubious savings.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Building regulations allow the option of connecting two heating units to one chimney. In such cases a 12 cm joint at a height of one metre from the bottom of the pipe connection must be provided>

Do not use materials with low density and high porosity such as foamed and slag blocks. The chimney must not pass through living quarters.

It is not permitted to install such structures also on closed loggias or balconies. In all rooms with a chimney, proper ventilation must be arranged.

Preliminary calculations of chimney parameters

The selection of a chimney should begin only after purchasing the boiler, otherwise it is impossible to select its cross-section and calculate the dimensions. The best shape is circular, although rectangular is also acceptable.

A tentative list of the structural elements of the chimney:

  • adapter connecting boiler spigot to chimney structure;
  • tube with revision hole and connector designed to collect condensate;
  • clamps for connecting individual chimney elements;
  • brackets and other fixation elements;
  • conical tip;
  • telescopic pipes;
  • outlets;
  • through spigot, etc. etc.

It must be remembered that it is generally advisable to install the outlets no more than two meters from the gas boiler spigot. This will ensure the most efficient draught.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The individual elements of the chimney construction for the gas boiler can be purchased in ready-made form. The main thing is to correctly calculate the dimensions of the construction and meet the safety requirements

For the correct installation of the chimney it is recommended to first calculate the cross-sectional area of the outlet opening.

To do this, use the formula:

F = (K ∙ Q) / (4.19 ∙ √ˉ H),


  • K - constant coefficient, its value varies between 0.02-0.03;
  • Q - capacity of the gas boiler specified in the technical certificate of the device;
  • H - design chimney height.

After the cross-sectional area has been calculated using this formula, it is necessary to compare the data obtained and correct them if necessary.

For example, according to the requirements for a gas boiler chimney, for circular designs the recommended cross-section depends on the capacity of the boiler and may leave:

  • 120 mm for a 24 kW boiler;
  • 130 mm for 30 kW;
  • 170 mm for 45 kW;
  • 190 mm for 55 kW;
  • 220 mm for 80 kW;
  • 230 mm for 100 kW.

If a rectangular cross-section chimney is installed, the heat output of the gas appliances is taken into account:

  • for appliances with less than 3.5 kW - 140x140 mm;
  • for appliances with 3.5-5.2 kW - 140x200 mm;
  • for appliances with 5.2-7.3 kW - 140x270 mm etc.

If asbestos cement pipes are used, the chimney section must be at least 100 mm. Vertical sections of the chimney are fixed to the wall with 2.5 m spacing, and on sloped sections the spacing should be more frequent - 1.5 m.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

Chimney pipes for a gas boiler may have a circular or square cross-section, but the dimensions of such cross-section must comply with established standards

The chimney height is chosen according to its location in relation to the roof ridge.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The chimney height given in the table is the minimum. If the calculation does not meet the condition that the usable cross-section of the pipe must be larger than the internal area of the heater, a smaller cross-section but longer pipe should be used.

Chimney installation options

Foundations must be built for the internal chimney. If you add a protective brick channel as well, it will minimize the amount of condensation. Sometimes chimneys are attached from the outside to the wall behind which the unit is located.

Interior chimney

Before the chimney is installed, a location is selected under it. Then mark the places where it will pass through the ceiling and roof. Carefully check the accuracy of the markings and make openings. The next step - making the connection pipe to the boiler chimney, and then mount the revision and tee.

Activate sheet steel, install the main bracket, the pipe is increased, if necessary, use the \"knees\". Spigots are used in the area of contact with the slab. Take a sheet of galvanized steel with a hole so that through it freely passed the pipe, fix it to the ceiling. To strengthen the joints used clamps. Every 2 m the chimney is fixed with clamps, and every 4 m - brackets.

Work is completed by checking the seams for tightness. To do this, take a soapy solution, apply it to all joints. If everything is done qualitatively, then when you connect the unit to the chimney, bubbles in these places will not appear.

Equipment of external construction

For the remote chimney in a blind wall make a hole of such diameter that the pipe with insulation freely passed through it. Installed in the hole the first element of the future chimney, fix it, wrap the insulation. The following sections are added from the street side, controlling the verticality with a plumb line.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The outside chimney is safer, but it must be well insulated. The purchased construction has all elements well fitted, so that the assembly will not cause problems

The pipe is fixed to the wall with brackets until it reaches the desired height. Finish the process by attaching the pipe to the boiler spigot and sealing the joints. In order for the external chimney to heat up quickly, it is insulated along its entire length with basalt wool.

Setting a coaxial flue

This type of chimney conveys combustion products outside and simultaneously supplies the boiler burner with oxygen-rich air. With this design, no additional ventilation is necessary.

The chimney is made of round pipes - the outside steel pipe is 10 cm in section and 0.1 - 0.2 cm wall thickness and the inside aluminum pipe is 6 cm in diameter. The pipes do not touch each other because there are crosspieces between them.

Coaxial flues are installed for closed chamber boilers made for wall and floor mounting as well as for boilers and other gas appliances.

This gas vent has several advantages:

  • the chimney is structured so that at the same time as the incoming air is heated, the exhaust gases are cooled;
  • the chimney increases the efficiency of the equipment;
  • It has compact dimensions, therefore it is used not only in private houses but also in city apartments;
  • safe - exhausted gases do not come into contact with the room air and do not exit through the ventilation duct but directly to the atmosphere;
  • easy to install.

The coaxial chimney can be installed either horizontally or vertically. Regardless of the installation method, the maximum length of the flue must not exceed 4 m. There are models with solid parameters, designed specifically for the chimney at a great distance.

Most coaxial chimney installation manufacturers produce adapters of special design used for vertical transitions through the ceiling and roof. In order to protect the system from precipitation and to ensure tightness in the area where the pipe passes through the ceiling, there are special hatchlings.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

The figure shows tips and mandatory requirements for the installation of coaxial type chimney. They all apply to gas flues for boilers with a capacity not exceeding 70 kW

When using a coaxial flue for a wall-mounted boiler, it is placed horizontally. It is necessary to ensure a 3-5% slope, otherwise condensation will enter the boiler.

The standards regulate not only the dimensions of the chimney itself for a gas boiler, but also the location of the hole in the wall. It must be at least 50 cm away from the window next to it and at least 25 cm if it is above a window.

How to remodel an old chimney?

If a gas boiler is included in a longstanding heating system instead of a conventional furnace, a brick chimney need not be completely rebuilt. It can be upgraded by guilding. This can be done in two ways.

Method #1.Install a stainless steel pipe in the base of the existing chimney.

The pipe should be chosen so that its height equals the height of the old chimney, and the diameter corresponded to the boiler spigot. The gap between the walls of the existing chimney and the pipe is filled with thermal insulation material such as cellular glass, expanded clay or perlite.

Method 2.Apply the Furan-Flex technology. This option is more expensive than the first one, but the chimney diameter remains unchanged. The material is frost-proof, does not corrode and the diameter varies from 6 - 100 cm.

Chimney for the gas boiler: standards and requirements for installation, a comparative overview of species

FuranFlex technology allows for quick and effective modernization or repair of chimney with maximum 30⁰ slope

The very technology consists in placing an elastic pipe inside the chimney under pressure. The pipe takes the shape of the chimney, then hardens and becomes a continuous seamless shell that does not allow any smoke or condensation to pass through.

Conclusions and helpful video on the subject

Video #1. For a detailed overview of installing a coaxial chimney designed for a gas boiler, see this video:

Video #2. Here is useful information on how to choose a chimney while avoiding common mistakes:

Video #3. Clip on fixing violations of technology installation chimney for a gas boiler:

Any household appliance, especially working on such an unsafe energy carrier, as gas, should be mounted with the observance of all the rules. The arrangement of combustion products removal from gas boilers requires a competent approach. First perform engineering calculations and only then implement the project, so it is better to trust all this to professionals.

Any questions about the device and installation of flue pipes for a gas boiler, have comments on the material, want to share experiences in the arrangement of the flue channel with their own hands? Please write your comments in the box below.


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