# Choosing a chimney pipe

## Recommendation points

The chimney is an integral part of any furnace system, its main purpose is to remove exhaust gases from the combustion site. Chimney design errors can lead to fire or poisoning by combustion products. From this article you will learn about the types of chimneys and the possibilities of their application..

## Calculation of the height of the chimney in design and construction

Before calculating the optimal chimney height, you need to evaluate a number of building parameters, such as roof thickness, roof slope angle, and distance from the vertical axis of the ridge. If the chimney is located at a distance of up to 150 cm relative to the vertical line of the ridge, then the height of the chimney above the ridge should not be less than 50 cm. If the chimney is located at a distance of 1.5 to 3 meters from the ridge, then the chimney must not be lower than the height of the ridge. If the chimney is more than 3 meters from the ridge, the height of the chimney should not be lower than a line drawn down at an angle of 10 degrees to the horizon from the ridge. Remember that the height of the umbrella covering the pipe is not taken into account in the calculations..

When calculating the height of the chimney, do not be guided only by the principle of financial savings – if you decide to maximize the height of the pipe with its minimum volume, the draft will sharply decrease throughout the system, which can lead to the ingress of combustion products.

## Chimney designs

Currently, two types of chimneys are used in construction, depending on their design:

1. Direct-flow chimneys – are used to remove hot air and combustion products through the channel vertically upwards. They are suitable for brick ovens and fireplaces that heat a room with an open fire. Direct-flow brick chimney is the most popular and capital option.
2. Elbow chimneys – work on the principle of once-through, but make it possible to integrate several stoves into one system for efficient heat distribution. They are made mainly for brick ovens, the main function of which is to heat the premises..

## Types of chimneys by material of manufacture

Chimneys today are made from different materials, each of which is suitable for the use of certain types of fuel. The most popular are brick, coax, asbestos, stainless steel, and ceramic. Let’s take a closer look at each type of chimney and identify their strengths and weaknesses.

### Brick chimney

It is made of molding bricks of the grade not lower than M-200 for the inside of the chimney (under the roof of the building) and grade M-250 for external masonry. According to fire safety requirements, the minimum area of ​​the chimney for the removal of furnace gases must be at least 250 sq. see This is achieved by keeping the masonry in a circle of one and a half bricks. Under the roof, the masonry is laid on clay mortar with the addition of refractory additives, the outer part – on cement mortar of increased strength (1: 3). A brick chimney is used for heating, sauna stoves, fireplaces and other stove systems, in which high storage capacity is important for retaining heat, as well as for frequent (daily) use. It is not recommended to use sand-lime brick for the upper part of the chimney.

Pros: good thermal conductivity, reliability, resistance to acidic effects of condensates inside the chimney duct, durability.

Minuses: large weight, complexity of installation and maintenance, inability to work with boilers with low flue gas temperature, rapid accumulation of soot due to the roughness of the inner surface.

### Stainless steel chimney

Modern technologies and a reduction in the cost of the final cost of products made it possible to use stainless steel pipes for arranging the removal of furnace gases from the furnace. As a rule, ready-made chimneys of a certain diameter (110 and 220 mm) and a certain length – 500, 1000 and 1500 mm are produced today. In most cases, the chimney runs in the wall or is mounted to the outside of the building. The design of the pipe includes a special seat, which simplifies installation.

A stainless steel chimney is used for sauna stoves, country heating systems, as well as for heating greenhouses and other outbuildings.

Pros: low cost, ease of installation, durability, resistance to acid media.

Minuses: high heat transfer, not fireproof, requires additional protection with a layer of refractory material with a good heat-absorbing effect (foil basalt cardboard – 50 mm).

### Coaxial chimney

Partially the cons of the stainless steel chimney was solved by the creation of a coaxial chimney. This pipe resembles a layer cake of three components – a stainless steel gas exhaust duct, a heat-shielding layer and an external circuit made of galvanized or stainless steel.

They are used in gas boilers, radiators and convectors, where the air necessary for fuel combustion is taken from the street through an external pipe, and not from the room. In this case, the combustion products go outside through the inner pipe of the chimney, which eliminates the need to install an additional ventilation system.

Pros: durability, ease of installation, the ability to connect additional furnace systems, the ability to use for smoke removal in heating systems of residential buildings.

Minuses: the high price of the chimney itself, fittings and additional devices, the formation of condensate in the air supply channel can cause icing, which in turn will require additional thermal insulation.

### Chimney made of asbestos-cement pipes

Since the middle of the 20th century, asbestos-cement pipes with a high refractory coefficient have been used in the arrangement of the exhaust of furnace gases. They are available for arranging chimneys of two diameters – 110 and 220 mm.

Currently, the use of asbestos pipes for arranging chimneys in solid fuel furnaces is prohibited, since the maximum temperature that such a chimney can withstand is no more than 300 degrees Celsius.

However, if precautions are taken, asbestos-cement pipes can still be used to equip a chimney. Installation should be carried out in areas as far as possible from the furnace. In addition, a “sandwich” can be made from asbestos-cement pipe using an external casing, which will increase fire safety and reduce condensation.

Pros: low cost resulting from ease of manufacture and high prevalence of material, ease of installation, low weight.

Minuses: does not withstand temperatures above 300 degrees; quickly absorbs condensate due to the porous structure, which causes cracks, and they, in turn, cause fires; soot quickly settles on the inner walls, which is difficult to clean due to the design features; unpleasant odor and stains on the walls (when used for a sauna stove).

### Ceramic chimney

The use of ceramics for arranging chimneys is due to the versatility of the material – it looks good, withstands any atmospheric influences, does not burn. Such chimneys consist of special ceramic blocks, thermal insulation and a supporting frame made of lightweight concrete.

Ceramic chimneys are used for liquid and solid fuel boilers, sauna stoves and fireplaces.

Pros: durability, environmental friendliness, resistance to acids, high temperatures and moisture, the ability to use in high pressure conditions, low roughness of the inner surface.

Minuses: limited size range, the impossibility of constructing a tortuous channel, fragility – the slightest distortion or impact will render the pipe unusable, which complicates the installation process.

## Tips for choosing a chimney

Behind the seeming simplicity of the task of arranging a chimney is a complex and accurate calculation system. Therefore, before choosing one or another type of chimney, you need to answer a few questions:

• which stove will be used indoors;
• how much gas you need to remove;
• how often you will use the oven systems;
• what foundation is used under the stove.

For sauna stoves, barbecues and barbecues, a stainless steel chimney will be optimal. For country houses, fireplaces located on the upper floors, in apartments and other residential premises, a coaxial chimney is suitable. For brick heating stoves and fireplaces, a brick chimney is ideal..

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