When boilers burn various types of fuel, combustion products are heated up to a temperature of 70 ... 400 ° C (sometimes up to 1000 degrees). To throw harmful gases out, chimneys made of the following materials are used:
- brick;
- ceramic;
- metal;
- asbestos-cement;
- combined, for example, brick + stainless steel.
Our task is to consider the pros and cons of these options, and then find out which pipe is better to choose for the chimney of a private house, bathhouse and other heated buildings.
Natural draft flue selection criteria
Selecting the material of the future chimney, most homeowners focus on the price of products and the cost of installation. For reliable and safe operation of heating equipment, other factors will have to be considered:
- Chimney compatibility with boiler type. High-efficiency units (gas, diesel) emit smoke with a temperature of 70 ... 120 ° C, brick stoves and solid fuel heat generators - 150 ... 200 ° C, steel and cast iron stoves - up to 400 degrees.
- The method of installation of the gas duct is an internal gasket with a passage through the ceilings and the roof or an external installation along the wall.
- Flammability of the material from which the building is built.
- The ability to withstand the increase in temperature of the combustion exhaust products up to 1000 degrees. Such emergencies occur when ignition of soot accumulated inside the pipe.
- Resistance to corrosion, durability.
Reference. At the exit of the sauna stove or wood-burning heating boiler, the chimney can be heated up to 500-600 ° C.
Before choosing the material of the chimney, decide on the option of laying it and sketch a diagram. Recall the requirements for smoke pipes:
- the diameter (cross-sectional area) of the channel is not less than the output of the boiler, stove or fireplace;
- the minimum height of the pipe is 5 m, it is considered from the grates (burners) to the upper cut;
- the tip of the chimney should not fall into the area of wind backwater formed behind the gable roof ridge or standing high up to the back;
- maximum number of channel turns by 90 ° - no more than three;
- indent by unprotected insulation of the pipe surface from combustible (wooden) building structures - 50 cm, protected - 38 cm;
- the length of the horizontal section connected to the boiler nozzle is a maximum of 1 m;
- according to fire safety requirements, all metal flues laid through rooms and the attic of a house are subject to insulation with non-combustible material - basalt or kaolin wool.
The chimney for the furnace or boiler must provide a stable natural draft and removal of harmful gases out of the room - this is the main requirement. It is equally important to comply with other fire regulations, for example, do not use corrugated aluminum hoses on heating boilers.
Brick Chimneys - Pros and Cons
Such pipes are laid out from red solid brick, usually inside buildings, external attached options are less common. Masonry mortar consists of clay, sand and cement.
Note. Cement is not used in the masonry - there the solution is mixed with sand and clay. The chimney is heated less than the body of the furnace and washed by precipitation, so the addition of cement is necessary.
Homeowners have to deal with brick ducts in 2 cases:
- the project provides for the location of the smoke channel inside the house - next to the exhaust shafts of the ventilation unit;
- during the construction of a stationary stove or a classic fireplace.
Previously, red brick was considered the ideal material for building a chimney, but with the advent of new products it lost its leading position. Advantages of brick gas ducts:
- A presentable appearance that lasts for a long time - during the entire period of operation.
- A shaft passing inside the wall transfers part of the flue gas heat to the rooms.
- Stones and binder are non-combustible materials.
- A correctly folded pipe successfully resists heating to 1000+ degrees when burning soot (an example is shown in the photo). But with repeated or prolonged exposure to high temperature, the structure will begin to collapse and become fire hazard.
Reference. Ignition of soot in a stone chimney leads to a fire if: cracks remain in the masonry, cracks form, or the furnace cutting was performed incorrectly. Fourth option: sometimes mortar joints between bricks are eaten by mice living in the attic.
The disadvantages of brick pipes are much greater:
- The uneven inner surface of the channel contributes to the deposition and accumulation of soot, which ignites in the event of overflow.
- The rectangular (or square) shape of the shaft plus the roughness of the walls increases the aerodynamic resistance of the pipe and reduces natural traction.
- The construction is quite heavy and bulky, requiring foundation laying. Building a chimney or a stove entirely with your own hands is not an easy task; hiring performers is expensive.
- Due to the masonry, the dimensions of the channel are tied to the dimensions of the bricks, for example, 14 x 14, 14 x 21 or 21 x 27 cm. The standard sections of the shafts are presented in the table.
- When paired with a gas boiler, a brick chimney is destroyed by condensate.
Note. Any flue needs periodic cleaning; accordingly, we did not add this fact to the list of shortcomings.
How to deal with the shortcomings of brick mines:
- make external thermal insulation of the street pipe section;
- lay a stainless steel sleeve inside the channel - make a combined gas duct;
- operate the chimney together with a solid fuel boiler or stove - gases quickly warm the walls of the mine, condensate practically does not drop out;
- to lay out double brick walls, the inner row is made of industrial stone of the ШБ-8 type.
Features of ceramic channels
The flue is a capital structure, built from rectangular sections 330 mm high. Each module consists of 3 elements:
- ceramic inner tube 6-15 mm thick (with a diameter of up to 30 cm);
- thermal insulation layer of basalt non-combustible fiber with a density of at least 100 kg / m³;
- outdoor supporting block made of concrete with vertical openings for reinforcement and ventilation ducts.
Reference. The well-known European manufacturer Schiedel makes ceramic chimneys of the QUADRO series with additional air ducts designed for gas heaters with a closed combustion chamber. The chimney is connected to a turbocharged boiler instead of a double coaxial pipe.
Mounting a sectional shaft is much easier than building one from brick. But you can hardly do without masters - it is important to observe the assembly technology and accuracy - the ceramic core is fragile and afraid of shock. Mounting Features:
- The blocks are installed one on top of the other and fastened with cement mortar M150.
- Inside, a basalt heater is laid in such a way as not to block the air ducts.
- Pipes are tightly inserted into the insulating sheath and fastened with a special heat-resistant mass.
- To connect the outlet to the boiler, one of the block walls is cut out by a grinder. If necessary, section fastening is used - metal rods inserted into the corner holes.
The same Schiedel produces Kerastar combined chimney systems, outwardly resembling conventional iron pipes.Here, stainless steel plays the role of the outer frame of thin-walled ceramics (6 mm), insulated with dense basalt wool.
Advantages of smoke ceramic mines:
- durability - the service life of the structure is equal to the period of operation of the building itself;
- operating temperature - 400 ... 600 ° C, maximum - 1000 ° C, the gas duct can easily withstand soot burning;
- low roughness of the inner surface of the pipe, hence the low aerodynamic resistance of the chimney and a small amount of soot on the walls;
- combustibility of materials - zero; ceramics are recommended for laying a gas duct inside the building;
- chemical resistance of the transported aggressive environment;
- compatibility with any types of fuel and various coppers.
The obvious minus of ceramics is the high cost compared to chimneys made of stainless steel and other materials. Brick will also be cheaper, but masonry work will easily “eat up” the price difference.
Note. There are cheaper analogues manufactured in the CIS countries, for example, AWT chimneys. The quality of the products is at an acceptable level, see the video for a description.
The second drawback is not so critical - the weight of the products is approximately 100 kg per 1 meter of running pipe. A standard design with a height of up to 7 m will “tighten” 700-800 kg, a reliable foundation will be required for installation.
Metal chimneys - advantages and disadvantages
In private house-building 3 types of such flues are used:
- ordinary pipes made of ferrous metal and galvanized;
- the same is made of stainless steel;
- modular systems of double-walled sandwich chimneys.
The first 2 options are used in farm buildings - greenhouses, sheds, garages. They are connected to wood stoves and other heat sources that work periodically. The advantages of single-walled pipes are an affordable price and ease of installation.
Cons are much more:
- galvanized and “black” chimneys quite quickly burn out and are fire hazardous;
- when connected to a gas column or boiler, a lot of condensation forms - the outer section of the pipe must be insulated;
- for the same reason, the channel is clogged with soot when the chimney is working with a TT boiler;
- metal is exposed to corrosion.
For these reasons, single-wall steel gas ducts are unacceptable to use in residential buildings. Corrosion-proof systems are used in Russian baths, but with the obligatory observance of building codes regarding fire safety.
Smoke metal sandwich pipes consist of 3 layers:
- stainless steel inner channel 0.5–0.6 mm thick;
- heat-insulating “shirt” - stone or kaolin cotton wool 25 ... 60 mm;
- outer shell made of stainless or galvanized steel 0.5 mm.
Reference. Basalt filler withstands heating up to 600 degrees, then begins to collapse (crumbles). Refractory mullite-siliceous (kaolin) fiber is designed for temperatures up to 800 ° C, but is rarely used by manufacturers.
The main difference between sandwiches and classical stone chimneys is the ability to deviate from the vertical and bypass obstacles (roof overhang, elements of the rafter system). Other positive points:
- Reasonable cost and low weight of products.
- Installation speed - when properly prepared, the external structure is assembled in 1 day without the involvement of specialists.
- Minimum roughness of the inner stainless walls.
- A wide selection of fittings - adapters, elbows of 90 and 45 degrees, finished tees with a bend of 89 ° (1 ° - the slope of the horizontal section towards the boiler).
- Systems are suitable for all types of boiler equipment.
- Pleasant appearance.
The lining of sandwich pipes retains its characteristic luster only when it is made of stainless steel. The galvanized casing becomes cloudy after 1-2 years, and the metal with a poor-quality coating has time to rust.
Now we will reveal the problem points of chimneys of the sandwich type:
- iron gradually wears out and burns out, the resource of the pipe is limited;
- the flue hidden behind the interior decoration cannot be controlled and the signs of burnout detected in a timely manner; there is a danger of ignition and fire;
- since the sandwich is relatively easy to manufacture, the market is flooded with poor quality products;
- heating to a temperature of 1000 ° C the pipeline can withstand once and for a short time, after an emergency event, the structure must be disassembled and changed.
Why you need to throw away a steel sandwich after burning soot. At a temperature of 900 degrees or more, the structure of the metal, including stainless steel, changes irreversibly, the strength of the material decreases. The second nuance: from heating, the steel expands greatly, the inner pipe lengthens and deforms, the longitudinal factory seam loses tightness.
Asbestos pipe - cheap and cheerful?
Asbestos-cement pipelines manufactured by industry are used to transport various liquids. But to use them as chimneys has become a long tradition, the reason is the affordable price.
Note. Asbestos is an excellent refractory material used to make cords, fiber boards and other heat-resistant elements. An asbestos-cement pipe is also a non-combustible product, it will not flare up from direct exposure to a flame, but can crack due to its own fragility.
Asbestos chimneys outperform other materials in price and are comparable in durability to them. The rest is entirely flaws:
- the pipe is quite heavy, a foundation is required;
- without fittings, a vertical shaft is not easy to connect to the boiler and organize the removal of condensate;
- the cement surface is rough, contributes to the sedimentation of soot;
- material bursts from shock or excessive heat.
Products are often used for ventilation of garages and cellars, as well as for the restoration of brick chimneys destroyed by condensate. Asbestos pipe is inserted inside the mine, which extends the "life" of the old building.
How to choose a chimney - tips
The first recommendation is that if the budget and installation conditions allow, it is always better to build a ceramic shaft inside the house. For stability, you can make a framing of hollow bricks or lean the chimney against a building structure - a partition, a wall. Ceramics will successfully work with any heating equipment - an oven, diesel boiler or fireplace.
Tip. If you plan to put a chimney outside the building and exit the pipe horizontally through the wall, buying ceramics is impractical. It’s easier and cheaper to organize the exhaust gas using a modular sandwich, attached to the outer wall of the house.
How to choose the right chimney material, depending on specific conditions:
- The cheapest option of finished products is a three-layer stainless steel sandwich + stone wool + galvanization. The material is perfect for working with efficient gas boilers that emit low temperature smoke.
- When the flue is located inside the dwelling, try, again, to purchase and install ceramics. Another way is to erect a brick shaft, insert a stainless sleeve inside.
- For outdoor use a sandwich, this is the most practical option. When choosing products of a particular manufacturer, examine the seams of the inner inserts - they should be boiled into a solid. Spot welding and seam connection are not suitable.
- If you are limited in funds, make a sandwich yourself - get a stainless pipe, a dense basalt insulation and bend the casing from galvanization.
- When building a fireplace or stove according to the finished project, it is not necessary to drive the brick pipe to the full height. Go through the ceiling (in a wooden house, perform a fire cutting) and switch to metal using a diffuser, as shown in the photo.
- If the section of the already built brick channel does not allow you to insert an iron sleeve, connect the boiler directly.But remember - from a gas heat generator the mine will begin to collapse, while a wood mine will become clogged with soot. The output is insulation and pipe cleaning.
- There is no need to buy any chimneys of natural draft for a turbocharged gas-fired boiler. Install the coaxial pipe horizontally and out through the wall.
Conclusion. The most reliable and durable chimney is ceramic. The second place in the ranking is firmly held by a metal sandwich, and the third is traditional brick. Simple iron pipes, asbestos and aluminum corrugations are not suitable for residential premises.
Conclusion
In fact, the choice among chimneys is small - ceramics or a sandwich. Brick loses the specified materials in efficiency, complexity of construction and price. Exotic options - chimneys made of vermiculite and glass - we did not seriously consider, since they were not widely used.