Firewood combustion temperature in a stove, boiler and fireplace: thermal properties, influencing factors, how to measure

The chimney is one of the most important elements of the installation of heating equipment, through which combustion products are removed from the room. Thus, how safe it will be to live in a house will be determined by the quality of the materials used and the performance of the structure. Smoke sandwich pipes made of stainless steel have all the required parameters for complete safety. In addition, installation of the structure does not cause difficulties.

Sandwich pipe Vesuvius 0.5 m

How does draft in a stove affect combustion?

If a small amount of oxygen enters the combustion chamber of the furnace, then the intensity and temperature of wood combustion decreases, and at the same time its heat transfer decreases.
Many people like to close the vent in the stove to increase the burning time of one bookmark, however, as a result, the fuel burns with a lower efficiency. If wood is burned in an open fireplace, then oxygen freely enters the combustion chamber. In this case, the draft depends mainly on the parameters of the chimney.

Under optimal conditions, the formula for a thermochemical reaction looks something like this:

This means that with the access of oxygen, hydrogen and carbon are burned, which results in heat energy, superheated steam and carbon dioxide.

For the highest combustion temperature of dry fuel, about 130% of the oxygen required for combustion should enter the combustion chamber. When the inlet dampers are closed, excess carbon monoxide is formed due to the lack of oxygen. Such unburnt carbon evaporates into the chimney, however, in the middle of the combustion chamber the combustion temperature drops and the heat transfer from the fuel decreases.

Modern solid fuel boilers are often equipped with specialized heat accumulators. These devices accumulate excess heat energy generated during fuel combustion under conditions of good traction and high efficiency. This option can save fuel.

In the case of wood-burning stoves, there are not very many opportunities to save wood, because they immediately release heat into the air. The stove itself is capable of storing only a minimal amount of heat, but a metal stove is not capable of this at all - excess heat from it immediately goes into the pipe.

Thus, by increasing the draft in the furnace, it is possible to achieve an increase in the intensity of fuel combustion and its heat transfer. However, in this case, heat loss increases significantly. If you ensure slow combustion of wood in the stove, then its heat release will be less, and the amount of carbon monoxide will be greater.

It should be noted that the efficiency of the heat generator directly affects the efficiency of burning wood. So, a boiler can boast 80% efficiency, and a stove - only 40%, and its design and material are of great importance. Similarly, the best option in terms of cost savings, as well as combustion efficiency and heat transfer, can be considered birch firewood

Because hardwoods with high heat output are not cheap, they are used much less often as firewood

Likewise, the best option in terms of cost savings, as well as combustion efficiency and heat transfer, can be considered birch firewood. Because hardwoods with high heat output are not cheap, they are used much less often as firewood.

Is it possible to connect two pipes to a chimney?

The question of the possibility of connecting two fireplaces to one chimney is controversial. According to the requirements of SNiP 41-01-2003, “for each furnace, as a rule, a separate chimney or channel should be provided. It is allowed to connect two stoves to one chimney, located in the same apartment on the same floor. When connecting chimneys, they should be provided with cuts (middle walls dividing the chimney into two channels. - Ed.) with a height of at least 1 m from the bottom of the pipe connection.”

As for the cutting, it can only be done in a brick chimney. If the chimney is modular, it is enough to use a tee to connect the pipe of the second firebox to the pipe of the first (if the smoke channels have different diameters, then the smaller one is cut into the larger one), after which it is necessary to increase the cross-section of the channel. How much? Some experts believe that if simultaneous operation of the furnaces is planned, then the cross-sectional area is determined by simple summation. Others believe that it is enough to “throw on” 30-50%, since two fireboxes will better warm up the common pipe and the draft will increase, but this only applies to chimneys with a height of more than 6 m.

"Baltvent-M"

Double-circuit tees and an adapter with which pipes of different diameters are joined.

Burda Media

Steel modules allow you to design chimneys of complex configurations, collect and discharge smoke condensate, and provide easy cleaning of pipes.

Raab

Some modular systems allow the installation of pipe sections up to 3 m long without additional fasteners.

When connecting two stoves located on different floors to one chimney, everything is much more complicated. Practice shows that such systems work, but only with careful calculation and numerous additional conditions (increasing the height of the chimney, installing dampers after the lower firebox and on the inlet pipe of the upper one, observing the firing order or completely eliminating simultaneous operation, etc.).

Please note that everything said in this section applies only to fireplaces with a closed firebox. An open firebox is more fire hazardous and requires draft, so it does not allow any “liberties” and requires the construction of a separate chimney.

What does pyrolysis gas consist of?

The type of wood does not affect the composition of the mixture during pyrolysis. Accordingly, birch, pine and spruce emit almost the same amount of all of the above gases. After pyrolysis 1 cu. m of wood you can get about 90 m3 of non-condensable gas.

The useful heat from the combustion of 1 m3 of non-condensable gas, kJ/m3, is calculated by the formula.

For example, let’s take a birch tree and calculate the calorie content of gas:

Qnr=127.5*28.4%+108.1*3.0%+358.8*18.2+604.4*1.4=11,321.62 kJ/m3= 11.3 MJ/m3

Then divide the resulting number by 4.187. Thus, Qnr will be equal to 2704 kcal/m3. For comparison, the calorific value of natural gas is 8000 kcal/m3.

How to properly install a stove in a garage?

The garage must have normal ventilation to ensure removal of combustion products in case of smoke. You should not install the stove close to the car; the distance should be no less than 1.5 meters.

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Rating of long burning stoves made of cast iron

Most experts recommend installing models made of cast iron, since their efficiency is much higher than that of other models. At the same time, they give off heat well, despite the small firebox. It is possible to use any solid fuel: firewood, coal and other types. The cost of such furnaces is higher, but their service life is longer. Some people worry that the appearance of cast iron fireplaces is not the same as that of ceramic ones.

Don’t worry: today craftsmen have learned to pay great attention to the aesthetic side of the issue.

Marseille 10

This is a small and beautiful fireplace from the Meta company. Suitable for heating summer cottages. Takes up little space, but has increased productivity. There is a viewing window here that will allow you to enjoy the view of the fire. It's big enough. In this case, smoke will not enter the room, which is an advantage over open-type fireplaces. Compared to steel structures, more thermal energy is required to achieve the desired result. But the heat remains 7 hours longer. The model is created so that it can fit into almost any interior.

Marseille 10

Characteristics:

wall type;
10 kW;
chimney 50 mm;
glass door;
lining – fireclay;
weight 105 kg.

pros

small size;
high performance;
stylish design;
large viewing window;
low price;
ease of installation;
comfortable handle.

Minuses

stands and attracts everyone's attention, the design is slightly inferior to more expensive models; its small size does not allow it to heat a large house.

oven META Marseille 10

Kratki Koza/K6

An excellent model that is included in the rating of fireplace stoves due to its stylish design, low price and high performance. The user can independently adjust the heat level using a special lever. It is responsible for supplying air to the firebox to control the combustion process. Thus, if it is necessary to extinguish a fire, the air supply must be stopped. This is an excellent option that allows you to avoid waiting for the fuel to burn out on its own. There are active and passive combustion modes. The former is used during the day, and the latter is needed to maintain temperature during the night. Glass can withstand temperatures up to 800 degrees.

Kratki Koza/K6

Characteristics:

wall type;
9 kW;
chimney 150 mm, connection to it is possible from above or from behind;
glass door;
lining – fireclay;
weight 120 kg.

pros

beautiful appearance;
good performance;
convenient control;
acceptable price;
you can enjoy the fire, the door is large enough;
several ways to install a chimney.

Minuses

you cannot cook food;
fuel only firewood or special briquettes.

Wood-burning stove-fireplace Kratki Koza K6

Ardenfire Corsica 12

A very reliable and beautiful stove for a summer residence, which is produced in France. It is compact and connected via the top panel. There is a function of secondary combustion and clean fire. The price is reasonable, and installation is usually not a problem. Suitable for rooms up to 200 sq. meters.

Ardenfire Corsica 12

Characteristics:

wall type;
12 kW;
connection to it is possible from above;
glass door;
lining – fireclay;
130 kg.

pros

looks beautiful;
convenient to manage;
there is pure fire and afterburning;
Efficiency 78%;
reliable and well-known manufacturer;
fuel - any solid materials, except fuel briquettes.

Minuses

heavy construction;
overpriced.

Ardenfire Corsica 12

Vermont Castings DutchWest XL

When studying the rating of long-burning fireplace stoves, you should definitely consider this model. It uses a patented combustion air system, which increases its efficiency. One supply of firewood can keep a room warm for up to 12 hours, which is an excellent indicator. The glass is treated with zinc oxide to increase strength. At the same time, it gives off more heat compared to standard fireproof. A built-in thermometer allows you to monitor the room temperature. Fuel is loaded through the front or rear doors.

Vermont Castings DutchWest XL

Characteristics:

wall type;
16 kW;
can be connected from the back or the side;
glass door;
lining – fireclay;
weight 280 kg.

pros

heating area up to 20 sq. meters, therefore suitable for large houses;
high efficiency (74%);
any fuel can be used;
pleasant appearance;
you can put something on top;
convenient and safe loading of fuel while the fireplace is operating;
there is a thermometer.

Minuses

heavy weight.

Vermont Castings DutchWest XL

These are the main wall-type models made of cast iron, which are included in the rating of long-burning heating stoves.

Peculiarities

Today, sandwich chimney pipes are increasingly used in heating systems. This is due to the high quality of the materials used, the performance and long service life of the structure, and its aesthetic appearance. Sandwich pipe is used throughout.

Installation of a sandwich pipe for a chimney

The interesting name of the “sandwich” pipes fully reflects the design principle. The chimney includes three layers, namely a pair of pipes that are located one inside the other, and thermal insulation that is laid between them. Stainless steel sandwich pipes have their own individual properties, which is why they are often preferred.

Installing a chimney with one layer is often irrational during house construction work. There are reasons for this, the main one is the accumulation of water vapor due to temperature differences between the combustion products that are removed from the premises and the air outside the walls of the home.

When using a sandwich type stainless steel chimney pipe, this issue is resolved by itself due to the presence of an insulating layer, which has a low thermal conductivity coefficient. However, it is still worth installing a condensate collector.

The thickness of the insulating layer should be at least 25 mm, but can reach 60 mm.

Sandwich pipes are available in different sizes, so choosing the right model based on diameter and length is not difficult. The range of this type of device includes various connection elements. Thus, connecting all corners, extensions and adapters will be easy and simple.

The effectiveness of removing combustible products from a living space will depend on the number of obstacles (pipe bends and turns) that are in their path. The ideal option is a single 90-degree upward turn. In cases where this is not possible, try to keep the number of turns to no more than three.

The service life of a sandwich pipe for a chimney, according to various estimates, is 10-15 years. However, user reviews often prove that it is necessary to replace the chimney after 5 years if it burns out.

The reasons for such a short service life may be different. This is both a manufacturing defect and an incorrectly selected type for a particular boiler.

In order for the structure to be operational for as long as possible, it is necessary to carry out preventive cleaning on time.

How does wood burn?

Not all wood burns the same. Some of them disappear almost completely in the furnaces, leaving only a handful of ashes in their place. Others smoke for a long time and tediously, clogging the entire combustion space with the remains of their combustion.

The speed and completeness of firewood combustion also depend not only on the chemical reactions occurring in the open flame, but also on the design of the stove. High-quality stoves have a rather complex structure, which includes many elements, such as a spool and ash pan, a firebox and grates.

The completeness of combustion of firewood will also be affected by its species, as well as (to a very significant extent) specific humidity.

burning wood

But strictly speaking, when calculating thermal devices, they usually do not take into account the different characteristics of firewood prepared from different types of wood. For calculations, the average statistical value is taken, which is 3800 calories for wood

Which wood burns hotter than others?

In addition to the calorific value, which characterizes the amount of thermal energy released when burning wood, in the course of practical life we may also be interested in heat output - that is, the maximum temperature that can be achieved in the firebox when burning one or another type of wood.

Different fuels and different types of wood burn in different ways. Some of them can produce an even and high flame, while others will demonstrate a low fire, but show a high temperature directly in the combustion area.

firewood heat output

There are two main points that affect the temperature produced by wood during combustion.

First of all, the combustion temperature depends on the intensity with which the oxygen necessary for combustion enters the firebox. This indicator is usually determined by the design of the firebox itself.

The design of the furnace itself also affects the temperature.

Stoves and fireboxes can be made from different materials. And each of the materials can have a special effect on the combustion temperature of firewood.

In a massive stone stove, the wood burns almost completely, but this process takes a relatively long time. On the other hand, a potbelly stove, that is, a firebox made of a thin steel sheet, cools down very quickly, distributing heat to the surrounding space. In this case, heat from the combustion zone is constantly transferred to the walls and further into the room. As a result, the firewood in such stoves burns with virtually no residue.

How to measure the burning temperature of wood?

You are unlikely to be able to measure the burning temperature of firewood with a regular thermometer. Moreover, it is completely lost to determine the combustion temperature “by eye”. In order to conduct such research, you need to stock up on a special device - a pyrometer.

But note that the highest burning temperature of firewood does not mean that firewood of this type can release more heat.

Please note that in good combustion devices, for example in closed fireplaces, it is possible to artificially reduce the supply of oxygen from the air to the burning wood, thereby increasing the combustion temperature and reducing heat transfer.

For comparison, you can look at another plate, which reflects the calorific values of various types of fossil fuels.

calorific value

Correct temperature in the steam room

A lot can be said about the rules of classic health bath procedures, but in this article we will dwell in detail on the temperature. If we talk about the temperature in the steam room that is most suitable for health in all respects, then this indicator lies between 50 ° C and 70 ° C

. In the classical Russian bathhouse, the stoves were always built of brick and, as a rule, they had closed heaters. This design was simply not able to heat the steam room above 60 ° C and in order to get a good sweat, it would have been necessary to sit in it for too long, but a way out was found.

A ladle of water was poured onto the stones, heated red from the direct flame, which instantly turned into light, hot, finely dispersed steam, most comfortable for both the respiratory tract and the skin. A cloud of steam rose to the ceiling and a person lying on the shelf was gradually doused with small portions of this steam using brooms. With the right technique of pumping steam onto various parts of the body, the steaming process brings not only unforgettable positive sensations, but also the strongest healing effect.

When designing your own sauna, it is important to understand that in addition to the correct temperature to obtain the full range of positive effects of steaming on the body, the sauna must also have a certain humidity. The optimal indicator is within 60%

It is this combination of temperature and humidity that provides ideal conditions for healing the entire body.

It is possible to ensure that the steam room has both the specified temperature and the correct humidity at the same time only if the stove is in it with a closed heater

To obtain high-quality finely dispersed steam, it is very important that the stones in the furnace are heated to at least 300 °C. And if the heater is open, then when the stones in it are heated to such an extent, the stove itself will be so hot that the temperature of the steam room will go beyond 70 ° C

Calculation of the volume of firewood for a bath

The volume of a car body and the volume of logs loaded into it are two different things. Since the process of accurately calculating the volume of densely stacked logs is quite complex, loggers and sellers use their own unit of measurement - a storage meter. It is taken to be a densely stacked woodpile, the height, width and depth of which corresponds to one meter.

One cubic meter of firewood is calculated with K=0.7. It turns out that 1 storage meter = 0.7 m 3 of firewood. Typically, logs are brought in bulk in a car. In order not to waste time on laying the woodpile and calculating its cubic capacity, the volume of the body is multiplied by K = 0.82 and the number of storage meters is determined. For example: with a car body length of 3.5 m, width of 2 m and side height of 1.5 m, its volume will be 10.5 m 3 .

Using K=0.82, we get 8.61 foldometers. With an additional coefficient of 0.7, the calculation will show the amount of firewood in the amount of about 6 m 3. This is almost 2 times less than the volume of the body. Using this calculation method, you will always accurately determine the amount of firewood you need to pay for.

How to chop firewood for a sauna - watch the video:

It is known that oak, birch or beech firewood produces more heat than pine, aspen, and alder. Moreover, hardwoods such as maple and oak retain heat longer and burn with a calm flame. They are best used for large combustion openings. Soft wood burns faster and produces a lot of sparks. Birch produces more soot, alder and especially aspen produce less; such firewood not only does not produce soot, but is also capable of burning it out of the chimney.

The calorific value of firewood depends on its moisture content and the type of wood. For example, 1 cubic meter of birch firewood is equivalent to 0.75 oak, 1.1 alder, 1.2 pine, 1.3 spruce, 1.5 aspen firewood. Dry firewood ignites easily and produces little ash; when burning, it develops a higher temperature, produces more heat, and is therefore more economical.

Aspen firewood cannot be cooked - it produces little heat. Only the poor burned their stoves with such wood all year round. Birch firewood differs from aspen not only in the composition of the wood, but also in density; it is much heavier.

The higher the density of wood, the more heat it produces during combustion. People called alder wood royal firewood. The wood of oak, ash, elm, as well as fruit trees: apple, pear, plum and cherry gives a lot of heat. Apple wood burns especially hot and smokeless. All types of willows burn hotly and without soot, but they burn out very quickly. Therefore, more willow firewood is used for one firebox than any other.

Wood of one species produces more ash, and another less. Experts call this property of wood ash content. Softwood from deciduous trees, such as poplar and willow, has a high ash content.

PINE FIREWOOD

Coniferous firewood is famous for its pleasant aroma of essential resins. Resins, when burned, release a substance that is useful during combustion.

But you need to be careful with pine firewood.

When burning, pine crackles and sparks can fly out! Resinous pine.

ASPEN FIREWOOD

Aspen firewood is not particularly popular. The fact is that if you do not mix aspen firewood with others, then there will be little fire from it. And it’s quite difficult to light aspen. But there are also big advantages. For example, aspen is cheaper in cost.

OAK FIREWOOD

Oak firewood is well suited for baths and fireplaces. Of all types of wood, oak has the highest heat transfer. Also, oak burns the longest, so you don’t have to frequently add new logs to the fire.

BIRCH FIREWOOD

Birch firewood is a symbol of the Russian village. Birch is a symbol of the nation. It’s also an excellent fuel that is affordable and versatile.

You should not often light a stove or fireplace with birch wood, because birch wood quickly clogs the chimney with tar and soot.

Dangerous temperature

For comparison, consider a number of studies conducted by scientists in the twentieth century to monitor the effects of regular visits to a steam room heated to extreme values of 110-130 °C.

Professor H. Their in the 80s of the last century put forward an assumption about the connection between high temperatures in Finnish saunas and the occurrence of cancer, which was subsequently confirmed by the results of a large study. After considering a significant number of cases of lung cancer in those who like to steam at 110-130 ° C, it was found that staying in a steam room heated to such temperatures contributes to the formation of this disease.

The fact is that you can only be in such conditions when the air in the room is very dry, and this eliminates the hydrostatic effect of steam on the body. As a result, the blood does not supply the lungs well enough and they become burned due to their inability to adapt to the elevated temperatures to the required extent.

A number of other studies have also discovered that exposure to the dry, highly heated air of a sauna negatively affects sperm production and also leads to digestive problems in children born to mothers who frequently visited such saunas during pregnancy.

The manufacturing technology of a sauna stove places special demands on the equipment of all its departments, including the chimney. Its design is slightly different from the chimney system of a home stove. It should ensure long-term heat conservation and safety for steam room visitors. Before organizing a chimney in a bathhouse, it is worth knowing several important nuances.

The design of sauna stoves includes 2 types of chimneys:

Indigenous. They are organized next to the stove, using a special pipe for connection, through which the smoke goes into the main channel. One chimney can be used for 2-3 stoves. The main thing is that its internal diameter has the appropriate parameters, and the pipes from each heating device are located at different heights;
Systems with a mounted pipe are mounted directly on the stove pipe and discharged through the roof. This chimney option is the most common for sauna stoves.

Classification of chimneys according to installation location includes 2 types:

External. Their main part is located on the street and fixed to the wall using a bracket. They are not particularly recommended for baths, as they quickly cool down, losing precious heat.
Internal. These are vertical structures with good traction, located inside the building.

Depending on the material used, chimneys are:

Brick. A traditional look, characterized by labor-intensive masonry and high requirements for compliance with all parameters. They have a lot of advantages: durability, fire safety, strength, good thermal insulation and heat accumulation. Disadvantages include the roughness and angularity of the inner surface on which soot deposits accumulate;
A metal chimney is faster to install and costs less. It has a perfectly smooth surface, but weaker heat-retaining characteristics;
A combined version, including 2 parts: the lower one is made of brick, the upper one is made of a modern sandwich pipe. Allows you to organize neat, small passages that are easier to cover with heat-resistant material.

Literature

Gaydon A.
Spectroscopy and combustion theory. - M.: Foreign Literature Publishing House, 1950. - 308 p.
Khitrin L.N.
Physics of combustion and explosion. - M.: Moscow University Publishing House, 1957. - 452 p.
Shchelkin K. I., Troshin Y. K.
Gas dynamics of combustion. - M.: Publishing House of the USSR Academy of Sciences, 1963. - 254 p.
Lewis B., Elbe G.
Combustion, flame and explosions in gases. 2nd ed. Per. from English edited by K. I. Shchelkina and A. A. Borisova. - M.: Mir, 1968. - 592 p.
Pokhil P. F., Maltsev V. M., Zaitsev V. M.
Methods for studying combustion and detonation processes. - M.: Nauka, 1969. - 301 p.
Novozhilov B.V.
Unsteady combustion of solid rocket fuels. - M.: Nauka, 1973. - 176 p.
Lawton J., Weinberg F.
Electrical aspects of combustion. - M.: Energy, 1976. - 296 p.
Zeldovich Ya. B., Barenblatt G. I., Librovich V. B., Makhviladze G. M.
Mathematical theory of combustion and explosion. - M.: Nauka, 1980. - 479 p.
(English)
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Technology for cleaning a clogged chimney

And finally, it is important to take care of regular chimney cleaning. Its most proven and oldest method, for example, is mechanical

To do this, pick up brushes, special weights, and sometimes even a sledgehammer with a crowbar. True, this work is so dirty that you will have to take everything out of the bathhouse in advance and cover the remaining surfaces with layers of newspaper.

The easiest way to clean the above is with a brush - to do this, just insert it into the chimney and gently push it upward until the resistance of the accumulated soot weakens. You just don’t need to turn it, otherwise you’ll have to take out this tool in parts later.

If small growths become noticeable in the pipe, you can use aspen firewood - when it burns, it creates excellent draft, which removes the ash from the pipe. In addition, aspen has dry and intense heat, which immediately burns the resinous substances in the pipe from the coniferous firebox. By the way, potato peelings have the same properties if they can be prepared in the required quantity.

But modern methods of chimney cleaning are becoming increasingly popular - these are chemical preparations that contain special substances that can carry soot with it during combustion, or loosen it so that it falls off on its own.

The best time to clean a sauna chimney is after rain. Simple maintenance and regular care for the cleanliness of the pipes - and the firewood in the bathhouse will burn to perfection!

Normal temperature of gases leaving the furnace

In order for the water present in hot gases to evaporate better, the temperature of the latter must be increased. On well-heated pipe walls, settled drops of moisture quickly evaporate.

The normal temperature of gases leaving the furnace before exiting into the pipe is 12O...14O°C, when leaving the pipe into the atmosphere - not lower than 100°C.

If the flue gases, when exiting into the chimney, that is, at the view, reach a temperature of about 250 ° C, then condensation does not form, draft improves, the stoves heat up faster, while consuming less fuel.

Thus, when firing the furnace, the temperature of the gases must be adjusted so that at the viewer it is within 250°C.

You should know that in the summer, condensation either does not form at all or occurs in small quantities. The formation of condensate largely depends on the size of the grate, the correctly raised hearth and the design of the furnace in a Russian stove, the size of the channel, the thickness of the walls, clay and height of the chimney, the temperature of its heating, the humidity of the fuel used, the temperature of the gases leaving the chimney and the excess number of chimneys in the stove.

The height of the chimney must be at least 5...6 m, counting from the level of the ash chamber or the hearth of a Russian stove. The thickness of the pipe walls should be half a brick, 20 mm). Thinner pipe walls heat up quickly and cool down quickly, which leads to the formation of condensation.

Such pipes must be insulated. Various cracks in the pipe and the stove, through which cold air penetrates, also contribute to the cooling of gases and the formation of condensation. When the cross-section of the pipe channel (chimney) is higher than required for a given stove, the flue gases rise through it very slowly and the cold outside air cools them in the pipe.

Sometimes, to improve draft in stoves, it is necessary to rearrange the pipes, reducing the size of the chimney, lowering or raising the height of the pipe on the roof. This is done until a satisfactory result is obtained. Where the chimney narrows, right angles should be cut off to ensure a smoother transition of gases.

Do-it-yourself stove laying

The sandwich chimney is heating up. Causes.

Heating the outer contour of a sandwich chimney is a natural physical process. To understand whether a working chimney poses a danger, you need to know the normal and permissible temperatures. Below is a calculated table of temperatures of the external chimney circuit. All values are given for typical insulated sandwich pipe diameters of 50 and 100 mm. Potentially dangerous temperatures for chimneys are indicated in red.

The following reasons can lead to dangerous heating of the external chimney circuit:

1. Thin steel inner tube. For solid fuel units (stoves, fireplaces, boilers), it is recommended to install a sandwich pipe with an internal contour with a thickness of 0.8 mm.

2. Thin thermal insulation of sandwich pipe. The thickness of the sandwich chimney insulation for solid fuel units (stoves, fireplaces, boilers) must be at least 50 mm, for sauna stoves - 100 mm.

3. Settlement or displacement of the heat insulator in the sandwich pipe as a result of improper installation and operation. To avoid this situation, use only sandwich pipes with non-shrink insulation technology.

4. Installation of a bottom plug with an insert (or a structurally similar element) when transitioning from a non-insulated pipe to a sandwich. The use of such an element is not recommended by manufacturers, because leads to direct heat transfer from the inner pipe to the outer circuit. For solid fuel units (stoves, fireplaces, boilers), it is recommended to use a lower end cap.

Main settings

The main parameters showing the quality of wood are its combustion temperature and heat transfer. Both characteristics are closely related to each other, because the more intense the burning of wood in a stove, the higher the temperature, the more heat is released into the environment.

When faced with different types of wood, you will notice that some burn well and brightly, releasing noticeable heat, while others smolder sluggishly, and there is practically no heat from them. And the point here is not that some firewood can be damp, while others can be dry. This is explained by the difference between different types of wood in composition, density, structure, and, as a consequence, in combustion temperature and the amount of heat generated.

After much research, scientists were able to determine the heat output and combustion temperature of the main tree species under ideal conditions. Two factors were taken as ideal conditions:

Almost complete absence of moisture in the wood.
Combustion in a confined space, provided that there is only enough oxygen in it to carry out the reaction.

Some of the most valuable wood species with excellent heat transfer characteristics are oak, beech, hornbeam and larch. However, firewood from these trees is rare and costs a lot of money, so shavings, sawdust, branches and other waste from industrial production and logging are usually used as fuel.

At the same time, in order to have a complete picture of the thermal characteristics of wood, it is advisable to study the specific heat of combustion of each type of wood, as well as to have an idea of their heat transfer. Heat transfer can be measured in various quantities related to the weight and volume of the fuel.

Good to know: Fuel briquettes of the RUF brand, main characteristics

When studying the thermal characteristics of different tree species, it is worth noting that oak and birch emit much more heat when burned than, for example, alder, aspen or pine. At the same time, you should not completely rely on tabular data, because in real life it is not possible to achieve ideal conditions, so the temperature in the firebox of a wood-burning stove can be significantly lower when burning similar firewood.

The values given in various tables are ideal and are intended to show the overall picture, while the real temperature in the furnace firebox will never reach such values, and this is explained by two simple and understandable factors:

It is impossible to achieve the maximum temperature primarily due to the fact that it is not possible to completely dry the firewood at home. For lighting fireplaces and stoves, wood with different levels of humidity is used, the one that is available.
Another important factor that reduces the combustion temperature of wood in a fireplace or stove is the lack of oxygen. We regulate the air flow with a damper, which we often cover.

Let's look at each of the identified problems separately.

Dangerous temperature

For comparison, consider a number of studies conducted by scientists in the twentieth century to monitor the effects of regular visits to a steam room heated to extreme values of 110-130 °C.
Professor H. Their in the 80s of the last century put forward an assumption about the connection between high temperatures in Finnish saunas and the occurrence of cancer, which was subsequently confirmed by the results of a large study. After considering a significant number of cases of lung cancer in those who like to steam at 110-130 ° C, it was found that staying in a steam room heated to such temperatures contributes to the formation of this disease.

Discussion “what is the temperature of the stove in the bath

"or about the temperature around the stove in the steam room - a lot. Unfortunately, they are all carried out on an intuitive level and only a few specialists devote entire studies to this issue using pyrometers, thermometers and other equipment. How does the temperature of a sauna and steam room oven actually differ from the one that the thermometer shows us?

Bath lovers are not builders and, for the most part, coordinate the stove modes with their feelings. The other half of the steamers glance at the thermometer. I decided to find out what the difference is between our perceptions, between the data from the needle of a universal thermometer and what a digital remote temperature meter will show us.

Some temperature measurement data puzzled me, which I wrote about in the conclusions after the video.

By and large, we are not interested in the temperature of the oven, but in the conditions in the steam room. Your own skin is more expensive than the lid of a piece of iron. Therefore, I measured everything where the laser pointer of the device was shooting. I wanted to document the temperature measurements with a diagram, but decided to make a video with remarks

Attention! I used a device with a maximum measurement threshold of 330 degrees (footage in the furnace firebox)

Schematic diagram

Boilers BKZ 160 are vertical water tube devices. Water circulation is natural. A drum is installed at the top of the structure, where the flows of water and steam are connected. The steam separation process takes place in remote cyclones. The units operate either with a vacuum in the firebox or under pressure.

The layout of the units is P/T-shaped or tower. The structure can use supports or be suspended. The U-shaped layout takes up much less space, while the draft devices are located at the zero level. Boilers are designed for different types of fuel, and calculations are carried out individually for the area where the boiler is located, taking into account local fuel resources.

Schematic diagram of the operation of single-drum boilers BKZ 160:

The fuel is fed into a vertical firebox, closed on all sides by screens, the top and bottom of which are connected by pipe manifolds.
On the front wall of the combustion chamber, burners are located on 2 tiers in the amount of 2 to 8 units, depending on the performance of the boiler.
In screens heated by flue gases, boiler water is heated to form a steam-water mixture.
The steam-water mixture, due to natural circulation, moves to the upper collector devices.
Next, the steam-water mixture enters the drum and is sent through remote separators to the steam collector.
Feed water heated in the economizer with high pressure is sent by pumps to the upper drum to replenish the volume of water that was removed from the water path by extracting superheated steam.
Through lower cooler pipes, boiler water is lowered from the drum into the lower manifold system of the screen manifold to repeat the heating cycle.
Steam, cleared of moisture in separators from the boiler drum, is sent to steam superheaters, of which several are installed: radiation and convection.
After the superheaters, the steam goes for industrial extraction to a steam turbine or for technological processes.
The boiler is equipped with a recuperative type air heater, where, due to the temperature of the flue gases, the air is heated for supply to the burner device. Usually a two-stage air heating system is installed, with temperatures up to 200 C.
The smoke exhauster maintains a vacuum in the firebox of minus 2 mm. V. Art.
After combustion, the flue gases are directed into the inter-tube space of the superheaters with a temperature of 1180 C, and then into the economizer with a temperature of 250 C and the air heating system with a temperature of 130 C. After which the smoke exhauster discharges the exhaust gases into the chimney.

Double layer steel chimneys

The Russian market is offered by companies Schiedel, Jeremias, Raab and Rosinox (Germany), Fineline (Hungary), Camin Wierer (Italy) and others. Among Russian manufacturers of similar products, Elites can also be mentioned.

For apartment-by-apartment heating in multi-storey buildings, leading chimney manufacturers recommend the LAS (air-gas) system. In this case, flue gases are removed through an internal pipe, and the air required for fuel combustion is supplied to the boiler through a channel between it and the walls of the shaft. The use of LAS makes it possible to operate gas heating units in a mode independent of the air exchange in the room, that is, this approach is most consistent with the requirements of SNiP 41-01-2003 (clause 6.2.2), which require the installation of heat generators in apartments exclusively with closed combustion chambers. These products, made from polymer materials, are offered on the Russian market, in particular, by the Viessmann company.

Condensing boilers, which are becoming increasingly popular, make good use of the latent heat of flue gases, the temperature of which drops to such an extent that condensation cannot be ruled out in the chimney even if the chimney is well insulated. As a means of combating corrosion of the internal walls of chimney pipes, Fineline recommends using a Furanflex polymer liner, which has a one-piece structure. This device is suitable for protecting brick and steel channels of any length, and its installation is carried out without breaking the wall. At the same time, polymers cannot withstand high temperatures, which is why they cannot be used to remove flue gases from stoves and fireplace inserts.

When installing a steel chimney at the exit of the structure from the wall, it is necessary to install additional fastenings, and elbows and bends are not supporting elements; they cannot be pressed against the external surfaces of the building

Resistance to humidity and chemically aggressive environments is the main advantage of modern ceramic chimney systems, which are suitable for working with any type of heating equipment. Made from high-quality technical ceramics, the chimney is impervious to moisture, acids and temperature changes, withstanding up to 1250°C. Such chimneys are mounted from ceramic blocks, and a reliable gas-tight connection is ensured by the design of the channel itself in combination with a special sealant. The disadvantages of such systems are their relatively large mass, volume, and high cost.

Wood Density

Depending on the structure and density of wood, as well as the amount and characteristics of resins, the combustion temperature of firewood, its calorific value, and the properties of the flame depend. If the wood is porous, it will burn very brightly and intensely, but it will not produce high combustion temperatures - the maximum value is 500 ℃. But denser wood, such as hornbeam, ash or beech, burns at a temperature of about 1000 ℃. The combustion temperature of birch (about 800 ℃), as well as oak and larch (900 ℃) is slightly lower. If we are talking about species such as spruce and pine, then they light up at approximately 620-630 ℃.

When choosing a type of firewood, it is worth considering the ratio of cost and heat capacity of a particular wood. As practice shows, the best option can be considered birch firewood, which has the best balance of these indicators. If you purchase more expensive firewood, the costs will be less effective.

To heat a house with a solid fuel boiler, it is not recommended to use types of wood such as spruce, pine or fir. The fact is that in this case, the combustion temperature of the wood in the boiler will not be high enough, and a lot of soot will accumulate on the chimneys.

Firewood made from alder, aspen, linden and poplar also has low thermal efficiency due to its porous structure. In addition, sometimes during the burning process alder and some other types of firewood shoot out coals. In the case of an open furnace, such micro-explosions can lead to fires.

In particular, if the wood has a loose and porous structure, it burns at fairly low temperatures, producing a light, high flame, and produces fairly little heat. But dense wood, although it flares up much worse, even with a weak and low flame gives a high temperature and a large amount of thermal energy.

Of course, in a pinch, any kind of firewood is suitable, including that obtained from a broken wooden box. But if we are talking about constant heating, then it is better to choose wood species characterized by the highest heat transfer. The heat transfer coefficient depends on several factors, including the density of the material.

Hardwoods are the same ones that are widely used in construction and decoration: oak, birch, beech. The greatest heat transfer is characteristic of oak, but since oak belongs to the category of valuable wood species, it is rarely used as fuel

Medium-hard - these include coniferous species - spruce, pine, larch, and fruit tree species - apple, pear. Logs made from them provide less heat, but flare up quickly and spread a wonderful aroma.
Soft ones - alder, aspen, are characterized by low heat transfer, but, due to the low moisture content, they burn with almost no soot formation. Such firewood is perfect for a fireplace, since the latter often serves as a decorative element rather than as an actual source of heat, like a stove.

It is no secret that logs made from freshly cut wood, regardless of the type, burn poorly: they do not flare up for a long time, produce less heat, smoke, and so on. In order for the combustion process to provide maximum heat, the wood must be well dried. The moisture content should not exceed more than 15-20%

To determine the degree of dryness, you can conduct a sound test: if a ringing sound is heard when two logs collide, then the firewood is ready for use.

Chimney materials

Before purchasing materials, you need to determine the structural features of the chimney.

Brick system

The construction is made of heat-resistant brick using a special dry mixture or oven clay. In addition, you may need material to create a fungus over the pipe.

Metal construction

Before purchasing material for the manufacture of a metal chimney in a bathhouse, it is necessary to draw up its exact diagram with the detailed location of all corners and turns of the pipe.

You will also need 2 iron sheets with holes corresponding to the diameter of the pipe. They are fixed on the ceiling of the bathhouse and on the floor of the attic. You will also need a heat-resistant material that will be secured around the pipe at the point where it exits into the wooden attic.

To create waterproofing around the chimney on the roof, you need to prepare a sealant or a special rubber seal.

Choosing pipes: what to look for

When purchasing iron chimney pipes, you need to decide on their cross-section. Basically, it depends on the power of the stove, but for most bath options this parameter is 15-20 cm. You should not take a diameter that is too large, as it will not retain heat well. And if it’s too small, it won’t create the draft necessary for removing smoke. Whatever it is, the cross-section of the pipe should not be less than the diameter of the outlet pipe of the heating structure.

There are a number of other requirements for the elements of a chimney in a bathhouse:

The minimum pipe height is 5 m. Neglecting this requirement may result in deterioration of traction. The exact value is calculated depending on the location of the pipe on the roof. In any case, it should rise above the ridge by at least half a meter. The ideal height from the ridge is 1.5 m, but this is not necessary;
The minimum thickness of the metal used to create the pipe is 1 mm;
If it is planned that the chimney system will be equipped with a hot water tank, then it must be reflected in a previously drawn up diagram. It is better if the tank is made of stainless steel.

Factors influencing the burning temperature of firewood

There are several factors that can affect combustion temperature - humidity and contact area. Understanding the degree of influence of one or another factor, you can achieve the highest flame temperature through simple manipulations with firewood.

Wood humidity

All fresh wood contains a certain amount of moisture. This can be: tree sap, resin, as well as water in the trunk absorbed by the roots

It is also important that water remains on the tree bark, especially after recent rainfall. As a rule, freshly cut wood contains from 40 to 50% moisture, and some varieties can reach up to 65% (tropical, coastal, swamp and moisture-loving trees)

That is why, when harvesting firewood, as well as in the production of lumber and furniture, the wood undergoes long-term drying, which can last for several years. However, this does not completely rid the wood of moisture; about 15-20% of water remains, so before burning you can observe evaporating white steam from the firewood.

If you build a fire from fresh wood, the combustion temperature will be lower. This is due to the fact that about 50% of the heat generated will go to evaporate moisture. The fire often makes loud popping and fumbling sounds - this is the sound of water evaporating inside the wood. You should definitely take into account that you will need twice as much firewood for a fire outdoors or in the cold season, because wet wood takes longer to burn and produces less heat than dry wood.

Special moisture meters are used to measure wood moisture.

Determining the moisture content of firewood

Contact area

The size of the wood can be a hindrance when starting a fire. After all, the larger the log, the higher the requirements for drying and heating. In this regard, large logs take a long time to flare up and do not burn as intensely.

To avoid this, you need to cut the wood into small pieces. This will provide a number of advantages:

Moisture will evaporate faster
The influx to places of combustion will increase
More pyrolysis gas will be released
The overall temperature inside the fire will increase.

This is why it is important to split wet firewood into small pieces. This way the fire will light up faster and the flame will burn more intensely.

Small chopped firewood

Advantages and disadvantages of ceramic chimneys for fireplaces

The advantages of a ceramic pipe include the following characteristics:

the material is very quick to install and assemble;
is a guarantee of high efficiency;
long service life;
the range of blocks is large, which makes it possible to mount a chimney opening with any configuration;
the presence of a special hole that makes it possible to clean the chimney;
the condensate that appears drains away thanks to the hole located at the bottom of the chimney.

Among the disadvantages of block ceramic pipe systems, it is customary to highlight the following:

relatively high price;
Due to the fact that most of these chimneys are manufactured abroad, the delivery time is sometimes very long.

A few words about air supply

Also, we must not forget about oxygen. From school courses, every reader knows that combustion requires oxygen - without it, the process simply will not start. More precisely, the process will proceed, but it will be the formation of coal from wood, and not combustion. In this case, we are interested in the latter.

The more oxygen in the firebox, the better the wood will burn and, therefore, release a large amount of energy. True, the fuel will burn faster than with a lack of oxygen.

If necessary, the burning rate can be changed by slightly opening and closing the damper of the stove or heating boiler. But it is worth considering that with a lack of oxygen, although the process is delayed, in general the amount of heat received is reduced. Therefore, artificially extending the combustion time cannot be called rational. The only case when this is justified is a bathhouse. The high temperature is not too important here, but the duration of combustion is a desirable factor so that the heat remains in the room for a long time.

To get maximum heat, you need to ensure a constant flow of oxygen - as people say, ensure good traction. Indeed, a cleaned chimney combined with a slightly open ashpit (a special door through which fresh air enters) allows fuel to be burned most efficiently.

Key points to consider when choosing a chimney

When choosing a chimney design, you need to pay attention to the following factors:

The chimney exhaust material needs to be stable so that it can withstand the high temperature of the exiting products; (See also: )
Must withstand a mixture of soot and condensation;
The design of the chimney must fully comply with all required standards (construction, fire, technological, operational).

For a fireplace that will be fueled by gas, a chimney made of stainless steel is perfect; for coal, it is better to choose a chimney made of brick, and for firewood, a design made of ceramics, brick, and stainless steel is suitable.

Hardwood firewood

To make a choice, you need to consider each type of firewood separately.

Birch firewood

This type of wood has special qualities, so it is often used to fire saunas. The heat that birch gives is a disinfectant for the room and releases the fragrant aroma of a real Russian bath. In addition, it is also credited with medicinal properties that help speedy recovery during a cold. But birch firewood cannot be kept in woodpiles for more than two years - it loses its properties and begins to deteriorate, turning into dust.

Birch firewood

Dried birch wood, as well as its bark, has a high content of tar, which is a carbon compound, so firewood quickly ignites and burns together, without leaving behind a large amount of ash. Splinters made from dry birch logs are used to light other firewood made from heavier wood. When burning, birch gives off good heat transfer, releasing heat of such intensity that is 22-25% higher than the flame from aspen or pine wood.

Oak

Oak wood for heating a stove is considered an elite fuel, so it is quite expensive. Oak is a hard wood, it burns for a long time and has very good heat transfer, surpassing even birch firewood in this quality. For heating, middle-aged trees are harvested - they are the ones that have the properties described above. Oak firewood produces intense heat and spreads a tart forest aroma throughout the heated room, and this is especially felt if they are used to stoke a fireplace. The steam released by oak when burned, just like birch, has long been considered medicinal by people, especially for children.

Oak firewood

It is interesting that famous Italian restaurateurs and cafe owners, adhering to ancient traditions, use exclusively oak firewood to prepare real pizza, although such wood is rare and has a fairly high price. Firewood from the trunks of fruit trees, such as a pear or an apple tree of a certain age, has somewhat similar qualities, but it is quite difficult to find them in large quantities.

Alder firewood

Alder firewood is popular because it does not require special conditions for drying - it reaches the required humidity on its own. This happens because those alder species that grow in places where the soil does not have excessive moisture are selected for firewood. Such wood can retain its aromatic properties for more than three years, and also does not lose its other positive qualities. These include excellent heat transfer and low resin content - thanks to this quality, it produces less smoke when burning. Therefore, alder firewood has long been often used in bathhouses that are heated in black. Another good quality of this wood is that the evaporation from it helps clean the chimney of soot deposits.

Alder firewood

Alder has more than 25 species, and each of them has its own shade - beige and brown, bright red and almost white. By this feature, it can be easily distinguished from other wood.

If alder is sawed in the yard of the house, then you must place a piece of fabric or polyethylene under the sawing site to collect all the sawdust. They are useful for smoking meat and fish dishes, and they are also good to add to the grill when preparing barbecue.

Aspen

Aspen firewood, just like alder, helps clean soot deposits in the chimney. The flame from this firewood itself does not produce soot, but the rising aspen heat makes the soot already accumulated in the chimney loose, and it begins to separate and crumble into the firebox.

Aspen firewood

However, they also have a huge drawback - aspen firewood burns quickly, giving low heat transfer, so they are not popular and are rarely used, mainly for kindling or cleaning the stove.

Linden

Linden wood, although it burns slowly, gives excellent heat, and therefore good heat transfer. Almost any linden components - leaves, color, bark and wood - are medicinal. Therefore, such firewood was often used in baths - a little honey was added to it, which gave a unique thick aroma to the steam room, which was used to treat lung diseases or long-lasting wounds. After a bathhouse heated with linden wood, the patients were given tea with linden blossom and honey - it cleanses the respiratory system and also removes toxins from the body.

Linden firewood

The disadvantage of linden firewood is their short shelf life - no more than two years.

Chimney design

Each individual building and each fireplace requires a suitable chimney with individual parameters and characteristics.

Parameters by which you should select a chimney:

Chimney material;
The location of its structure;

Chimney made of steel. The steel chimney design includes pipes, insulation and an external circuit. Stainless or galvanized steel is used to make pipes. The steel chimney design is easy to install and lightweight.

Galvanized steel pipe has a lower cost, but it is less reliable than the previous model. Accordingly, the best chimneys are made of stainless steel.

Ceramic chimney design. Installing a ceramic chimney requires certain specialist training and, very important, accuracy. Ceramics provide excellent thermal insulation. The service life of the material is approximately 30 years. The ceramic structure consists of an internal ceramic liner, lightweight concrete blocks are located on the outside and, of course, a heat-insulating gasket that must be laid between the layers. (See also: )
Glass construction is considered the most expensive and is very difficult to install. Some installation experience is required, but the glass fits perfectly into the interior of the house and looks very impressive and irresistible. Glass is very resistant to the formation of corrosive plaque, heat from the resulting combustion products and any exposure to moisture. Undoubtedly, these advantages of the design bring it to a high level of use.