Choosing the optimal chimney for a gas boiler is a difficult, but quite feasible task. After all, I want it to be an extremely simple design to install and operate, and even with high efficiency. All requirements are met by the coaxial type, the installation of which can become a kind of “snag”. Do you agree?
We will help you understand fairly complex issues. We provide website visitors with extensive information on the rules for the construction of a coaxial chimney, on the selection and arrangement of the best option. Here you will find valuable tips on decorating sections of canals laid inside houses.
In our proposed article, the installation standards for a coaxial chimney are described in detail. Useful schemes for its competent assembly and installation are given. Information is confirmed and supplemented by photo selections and video guides.
The principle of operation and device
In the family of devices for the removal of combustion products, a coaxial chimney stands apart. This modern design is much more efficient and safer than a regular chimney. This system is ideal for boilers with a closed combustion chamber.
To make a coaxial chimney, you need to take two pipes of different diameters and put a narrow pipe inside a wide one. It is still necessary to connect the inside of the wide pipe and the outside of the narrow pipe with special jumpers so that the central axes of both pipes coincide. Well, the coaxial chimney is ready.
In practice, such a design, of course, is easier and more reliable to buy than to do. The cost of a coaxial chimney will be higher than the price of an ordinary stainless steel pipe, but the costs will pay off in full.
Image Gallery
Photo from
Coaxial chimney on a log pediment
Affordable option and price
Installation paired with any type of equipment
Vertical Coaxial Designs
Errors in installing a horizontal pipe
Insulated pipe modifications
The length of the horizontal sections
The output of the coaxial pipe on the pediment
A double pipe is necessary for the simultaneous performance of two functions. Combustion products are discharged from the boiler furnace through a narrow narrow pipe. And through the gap between the inner and outer pipes, air enters the combustion chamber, i.e. oxygen necessary for burning fuel.
This solution has a number of advantages. An alternative to a coaxial chimney is a traditional chimney combined with forced air injection into the combustion chamber.
In this case, air is usually taken from the room in which the boiler is installed. Coaxial chimney allows you to take air from the street and feed it directly into the furnace.
The diagram shows the general principle of the coaxial chimney, as well as its structure compared to a traditional chimney (+)
What happens in such a chimney during the operation of the boiler? Hot combustion products move outward through the inner pipe, and in the opposite direction there is a parallel stream of fresh cold air. The result is a completely natural heat transfer: hot gases give off heat to an adjacent cold stream.
Air enters the combustion chamber already in a heated state, which increases the overall efficiency of the boiler, because you do not need to spend precious kilojoules on heating the air masses. The temperature of the outer surface of the coaxial chimney is noticeably lower than when using a standard chimney. This circumstance also makes the design safer.
Another advantage of the coaxial chimney is the easier installation of the boiler, because you do not have to install a forced ventilation system. In addition, these structures have different requirements than traditional chimneys. As a result, the combustion product removal system takes up less space.
On the outside of the building, the coaxial chimney pipe looks much more concise and takes up less space than with an external installation of a traditional chimney
Coaxial chimneys are universal, they can be installed with gas boilers, and with devices that run on liquid or solid fuel. Chimneys with various diameters are available for sale, which makes it possible to select suitable pipes for a particular boiler.
Installation of a traditional chimney in an already constructed building is a rather complicated task. If the installation of the chimney was not provided during the design, you have to go through the overlap and the roof or take the chimney out.
A bulky structure can create problems both inside the building and outside. But coaxial designs are simpler and more compact. The conclusion of such a chimney to the outer wall looks concise, it will not spoil the appearance of the house.
Features of the installation of coaxial chimneys
Chimneys of this type can be installed horizontally or vertically. Preferred is the first option, which is considered simpler and takes up less space. In this case, a number of requirements should be observed:
- the distance from the pipe to the ground level on the outside of the house should be at least 2 m;
- the pipe must be at least half a meter horizontal from windows, doors, vents, etc .;
- the same distance to these objects should be maintained vertically;
- if a window is located above the ventilation duct, the distance to its lower edge must be at least one meter;
- the free space in front of the coaxial pipe should be at least one and a half meters, i.e. there should be no walls, fences, poles or other similar obstacles nearby;
- if there is no special device for collecting condensate, then the coaxial chimney pipe should be placed at a slope to the ground;
- the size of such a slope can vary between 3-12 degrees;
- removal of the chimney canal is not allowed outside, but in another room or structure: staircase, basement, tunnel, arch, etc .;
- a distance of at least 20 cm should be maintained between the elements of the chimney and gas pipes, if they pass side by side.
Separately, it is worth considering the situation when the outlet of the coaxial chimney pipe is located under the balcony or some kind of canopy. This is a perfectly acceptable situation, but it is necessary to take into account the following point.
It is necessary to mentally draw a circle in a plane perpendicular to the wall. The center of the circle will be the junction of the canopy and the wall, and the radius will be the length of the canopy or balcony.
The chimney pipe must extend beyond this conditional boundary. It turns out that the closer the hole for the chimney is to the canopy, the longer the outer part of the pipe should be.
This diagram clearly demonstrates the basic requirements for the placement of a coaxial chimney with respect to various objects located next to it (+)
It is believed that the length of the coaxial chimney when using a horizontal installation scheme cannot be more than three meters. This is a general rule from which there are exceptions. For example, some Ferroli chimney models may be four or five meters long.
The set of materials for installing a coaxial chimney depends on the type of its location, but in general, the list of elements can look like this:
- the chimney pipe itself;
- adapter for connecting the boiler to the chimney design;
- knee, tee, etc .;
- crimp clamps for reliable connection of elements.
Typically, the delivery of a coaxial chimney includes all the elements necessary for its installation. To pass a pipe through a wall, ceiling, or roof, fireproof gaskets must be used. They will prevent overheating and ignition of materials surrounding the chimney.
This diagram shows the individual elements of a coaxial chimney. If the pipe needs to be extended, additional parts for industrial production should be ordered (+)
Here is one of the options: a hole is made in the wall and a sleeve made of asbestos-cement pipe is inserted into it. Then the space between the surface of the coaxial pipe and the sleeve is filled with asbestos cord. All elements of the coaxial chimney must be manufactured in an industrial environment and meet established standards.
It is not recommended to use home-made designs even for an adapter. Some amateur craftsmen are trying to increase the length of the pipes using sealing tape and high-temperature sealant. But this option does not withstand any criticism in terms of security.
Basic Installation Requirements
The type of installation - horizontal or vertical - depends on the characteristics of the room in which the boiler will be placed. There should not be any foreign objects in the space between the boiler and the wall into which the coaxial chimney will be discharged; this is an important safety requirement.
At the same time, the place where the chimney pipe exits the wall and the boiler pipe to which it is connected must be separated by at least 1.5 m vertically. The pipe should also have a slight slope of about 3 degrees to ensure the outflow of moisture condensed on the surface of the communications.
The space between the boiler and the wall into which the coaxial chimney is discharged must not be cluttered with any foreign objects
The next important parameter is the diameter of the pipe and boiler nozzle. In size, they must match. In no case is it permissible to install a pipe whose diameter is narrower than the dimensions of the outlet pipe of the heating device.
Before starting installation, you should carefully study the technical data sheet and the device of the boiler to make sure that the dimensions of the pipe and chimney comply with the established standards. The boiler nozzle may be located on top or side. It is believed that the upper location of the nozzle simplifies installation.
The dimensions of the boiler nozzle for the chimney, adapter and coaxial pipe must correspond to each other. The use of a pipe of a smaller diameter is unacceptable
To connect the chimney pipe, an adapter is usually used in the form of a tee, elbow or a piece of a regular pipe. In this case, there should not be any obstacles to the advancement of gas and air masses inside the adapter.
If the length of the coaxial pipe has to be increased, care should be taken about the tightness of the connection. For this, crimp clamps are used. In the same way, adapters, elbows and other elements of the chimney are connected.
The individual elements of the coaxial chimney are inserted into each other so as not to create obstacles to the movement of air and combustion products. Joints are rigidly fixed with clamps (+)
It is not recommended to carry out a design that includes more than two knees. The total length of the coaxial chimney, consisting of several different directions, should be no more than three meters.
During the installation of the coaxial chimney, its lower elements are inserted into the upper ones and rigidly fixed with clamps. This connection method allows for good traction. Separate elements must enter each other to a depth of not less than half the diameter of the structure in accordance with the requirements for coaxial flues.
For reliability, the place where the pipe exits the outer wall is blown with foam. Special decorative grilles are installed on top to make the installation site look attractive. The grill can be glued with a suitable adhesive, such as liquid nails.
Part of the coaxial chimney laid indoors can be masked, for example, using a plasterboard box:
Image Gallery
Photo from
Step 1: Scaffold Frame Device
Step 2: Foaming the hole in the wall aisle
Step 3: Sewing the lower tier of the frame
Step 4: Installing the duct over the coaxial pipe
Incorrect Grade Problem
Regarding the slope of the coaxial chimney pipe, the question may arise: where exactly should it be directed? Some experts argue that condensate should drain towards the boiler. According to other masters, the slope should be done in the opposite direction, so that moisture flows down the pipe to the ground. In both cases, reasonable arguments are made.
It looks logical that the condensate droplets move as far as possible from the boiler. The firebox is protected from unnecessary moisture, which remains outside the house and naturally dissolves in the environment. Everything looks that way until the ambient temperature drops below zero.
Inspecting a coaxial chimney pipe is a natural but dangerous phenomenon. Ice deposits prevent the removal of combustion products and fresh air into the furnace
With the onset of frost on a coaxial pipe installed with a slope to the ground, the condensate droplets freeze, forming an ice crust. Icing can be observed both on the outer part of the chimney, and in the space between two pipes of a coaxial design.
This happens because the temperature of the external circuit of the chimney of this type is low, it is not enough to quickly melt the ice. As a result, ice deposits create obstacles to the normal flow of air into the furnace, as well as to the effective removal of combustion products.
And this reduces the efficiency of the device. Long operation of the boiler with an icy coaxial chimney can even lead to significant equipment damage. It turns out that in warm regions, where there is practically no frost even in winter, a coaxial chimney can be installed with a slope to the ground.
In all other cases, it is recommended to slope the pipe towards the boiler, which usually corresponds to the recommendations of the manufacturers of these structures. What to do with condensate, which with such an installation will drain to the heating device?
It's simple, you need to install and use a special container for collecting condensate. Such a condensate collector is a small device that copes with its tasks quite satisfactorily. Partially, the problem of freezing the chimney can be solved with the help of its insulation, but this measure does not give one hundred percent guarantees.
This diagram demonstrates the construction of a special element - a condensate collector. It picks up moisture droplets running down the coaxial pipe to the boiler and protects the equipment from corrosion.
Some craftsmen believe that it is possible to prevent condensate freezing in a coaxial chimney with a slope to the ground if the inner pipe is shortened, but experts do not recommend changing the design on their own.
On the issue of icing a coaxial chimney, there is also another interesting opinion: the larger the diameter of the pipe, the lower the likelihood of condensate freezing. While the craftsmen broke their spears, discussing the optimal slope of the coaxial chimney, the manufacturers took care of creating a special kit.
To prevent icing of the coaxial chimney, it is recommended to use a special model with an anti-icing tip. Air is drawn into such a pipe through openings on its underside.
This design is resistant to icing and is designed to operate in harsh Russian winters. This device is equipped with an extension nozzle for a gas outlet (i.e., inner) pipe.A narrow protective spiral is installed inside the nozzle. In this case, the holes for air intake along the edge of the outer pipe are located below.
Basics of choosing a horizontal or vertical type
It is not always possible to fulfill all the requirements for horizontal installation of a coaxial chimney. Difficulties can be encountered if the room where the boiler is installed is very small. The outside of the building may also be problematic. For example, if there are windows close to each other.
If necessary, a coaxial chimney can be discharged vertically through an inclined or flat roof using appropriate weather nozzles. The length of such a chimney depends on the power of the boiler connected to it (+)
It also happens that the distance to neighboring buildings is too small to provide normal draft coaxial chimney. If all conditions are not met during horizontal installation of the structure, vertical installation should be preferred, i.e. bring the pipe through the roof.
When installing a coaxial chimney vertically, as with a traditional pipe, brackets are used. They allow you to keep the structure in the correct position and at a distance from the walls.
When withdrawing a coaxial chimney through a roofing cake, special attention should be paid to fire safety issues. Insulating pipes should be used here, and the use of fire-resistant insulation is recommended.
Protective covers are also used to isolate the chimney from contact with other objects and materials. A small air gap should be left between the coaxial pipe and the overlap area, but the roof at the pipe exit point must be carefully closed. The junction of the pipe and the roof is covered with a dense protective casing.
Good ventilation device
It may seem that a heating device with a closed combustion chamber and the presence of a coaxial chimney saves home owners from the need to provide the boiler room with normal ventilation. Indeed, air enters the furnace from the outside, and the combustion products are removed through a reliable airtight channel.
However, the need to ventilate the room in which the boiler is installed is still necessary. To begin with, normal air exchange will help maintain the optimum humidity level in the room, which prevents the development of corrosion processes and protects the equipment casing from destruction.
And it should be noted that any system can fail over time. If the boiler room has good ventilation, then in the event of a breakdown, a small amount of carbon monoxide will be removed from the room naturally. As a result, the risk of accidental carbon monoxide poisoning becomes significantly lower.
Video # 1. The coaxial chimney device, the principle of its operation and installation features are presented in the following video material:
Video # 2. Here, the equipment of a coaxial chimney for industrial production is shown in detail:
Video # 3. Overview of the anti-icing coaxial kit:
Coaxial chimney - a convenient and easy to install device that can significantly improve life in the house. But for such a chimney to function efficiently, it is important to comply with the norms and requirements when installing it.
Do you have any questions while familiarizing yourself with the material, find flaws or have a desire to tell about your own experience in assembling and using a coaxial chimney? Please post comments in the block below the article. Leave posts with your opinion and a photo on the topic.