Do-it-yourself heat exchanger made of corrugated stainless steel. How to make an air heat exchanger for a chimney: a review using the example of a potbelly stove Heat exchanger for hot water for a stove pipe

Heating devices that use fuel combustion to produce heat are unable to function without a smoke exhaust duct.

Need for use

The last of the above elements gets rid of toxic combustion products that can be dangerous to human health. But the flue gases that leave the unit through the pipe, escaping into the atmosphere, carry away heat in a large volume. It could be used to heat rooms. In order for this deficiency to be corrected, a heat exchanger is installed on the chimney pipe. This device allows you to significantly increase the efficiency of the heating device.

Main varieties

Today there are several types of heat exchangers, their design is approximately similar, which can also be said about the operating principle of these devices. They have a hollow body that has inlet and outlet pipes. The braking device is located inside and is designed for flue gases. This system most often consists of dampers with cutouts that are mounted on axles. The elements can be rotated to form a zigzag flue of different lengths. Adjusting the position of the dampers allows you to select the most appropriate ratio of draft in the pipe and heat transfer efficiency. At the same time, operating safety standards are not violated at all. There are also the simplest versions of heat exchangers that do not have adjustable dampers.

Principle of operation

If you plan to install a heat exchanger, you should familiarize yourself with the operating principle of this device. The holes, which are located at the bottom of the device, draw in cold air, using the principle of convection. Air masses pass through the internal space, gases heat up. Through the holes located on top, heated air is pumped into the heated room. This allows you to significantly increase the efficiency of the device, reducing the amount of fuel consumed. As practice shows, the fuel consumption of a “potbelly stove” with a heat exchanger installed on the chimney is reduced by 3 times.

The heat exchanger cannot be installed only after the device has been selected. We should not forget that when heat is released in the flue, the combustion products quickly cool down. This causes the temperature difference in the pipe to decrease, and the drop in draft in the system occurs instantly. In order to eliminate this effect, adjustments are made using dampers or the most suitable size of the structure is selected.

depending on material

If you decide to install a heat exchanger, it is important to decide which model will be used. There are several varieties of such devices, depending on the material used. The most optimal is food grade stainless steel, which is also called austenitic. Its characteristics are not affected by difficult conditions, for example, elevated temperatures, but seams from welding do not crack; the reaction of nickel and oxygen leads to the formation of a layer of film on the surface, which is highly resistant to acids and salts.

If you install a heat exchanger on a heating chimney pipe made of this material, the device will be the most durable. But it is better to refuse zinc if the temperature affecting it exceeds 200 degrees. Once evaporation begins and the temperature is above 500 degrees, the concentration of harmful substances will exceed the maximum permissible level. However, if a zinc profile is available, it is best to test the heat exchanger. It is important to understand to what temperature it will heat up. If this limit is no more than 200 degrees, then there is no need to worry.

This profile has an advantage, which is expressed in the fact that the material helps to increase the intensity of air movement flowing around the compensator. This option is perfect if you need to warm up the room quickly enough. But such a need should not arise quite often. It is best not to install a zinc heat exchanger on a chimney pipe in a bathhouse, since the exposure temperature can be quite high. It is best to use a similar device for a stove in the country, which will be used from time to time.

Carrying out the installation

We can distinguish two modes of operation of the chimney heat exchanger, each of them differs in a certain heat transfer inside. The first option is to connect a portable tank of water to the heat exchanger, which will need to be heated. Compensation will occur on the inner pipe, and the heat exchanger will be heated by heat from the steam. This option will allow the water to heat up for quite a long time, since the temperature on the walls will be 100 degrees. If you decide to install a heat exchanger, you can use the “pipe on tin” technology. The essence of this option is that the chimney will have a pipe made of metal or copper, which heats itself and heats the air passing through it. Using argon welding or a torch, you can weld such a spiral to the chimney. Tin will act as a binding material, but it must be degreased using phosphoric acid. Such a solder will be durable and strong.

Using a hood for an attic space

You can buy a heat exchanger for a chimney pipe in St. Petersburg at an affordable price. If you decide to do the work yourself, then the installation may involve installing a hood that will work on the principle of a furnace with the appropriate name. This system works quite simply. The operation is that the rarefied air will tend to rise, and the cooled air will fall down. This option will be an excellent solution for simple metal chimneys, which are located in the area of ​​the second floor.

By using a hood you can reduce the risk of fire or burns. In order to ensure heat accumulation, some craftsmen surround heat exchangers of this type with a mesh with stones, which makes the device look more attractive. Thanks to this mechanism, the pipe will not heat above 170 degrees, and the hottest place will be near the gate.

Installation of a corrugated heat exchanger

A heat exchanger on a chimney pipe, the price of which is approximately 3,000 rubles, can be installed using the corrugation principle. The technology will be extremely simple and very practical. To carry out the work, you will need three corrugations, which are made of aluminum. These elements are wrapped around the chimney.

Such manipulations can be carried out on any floor of a private house, this also applies to the attic. The air will be heated in pipes from chimney systems, and the heated masses will be directed into the premises. Heating is practical, and there is no need to install stoves in each room; if the area is quite large, it will warm up to high temperatures.

Solid or liquid fuel stoves produce a large amount of heat, but a lot of it goes unhindered into the chimney. A heat exchanger for the chimney pipe will help you avoid losing useful energy and stop heating the street. A simple and compact device can increase heat transfer by virtually a third, without reducing the characteristics of the stove itself, but a number of factors should be taken into account, such as maintaining normal draft and the ability to clean the chimney, so as not to get into trouble with the heat exchanger.

Principle of operation

When burning liquid fuel or coal, especially in homemade stoves, the temperature of the gases at the entrance to the chimney reaches 600°C and even higher. Such temperatures are not needed to maintain active traction; they only worsen the situation. Nothing prevents you from taking part of the heat without compromising the functioning of the stove and releasing it to the air in the room or water in the heating or hot water system. So, if you reduce the gas temperature from 600°C to 400°C, then, depending on the quality of the heat exchanger and the volume of flowing gases, the heating power can reach several kilowatts.

The task is to ensure active heat exchange between superheated gases escaping from the stack and the target medium: water or air. The key is the contact area. Placing, for example, air ducts or a water pipe coil inside the chimney is not a good idea; even taking into account all the other features, any objects in the duct will only contribute to the formation of soot and condensation, which will quickly damage the chimney and, accordingly, turn the operation of the stove into a dangerous event for others.

There are three optimal options for heat removal from the chimney:

• Coil around the chimney.
• Water jacket. A larger diameter cylinder is placed over the chimney pipe and filled with coolant. Dividing the chimney channel into a group of channels of smaller diameter allows you to increase the contact area.
• Chimney brake. The chimney channel is formed in the form of a coil, a labyrinth, through which the movement of gases slows down, which increases heat transfer.

The first two options are suitable for forming a water circuit and using heat in a heating or hot water system. The third design is more suitable for local air heating.

All types of heat exchangers have features that should not be ignored. If the heated medium is water, then there is a problem with excessive heat transfer. When the chimney is already hot and the stove is actively heating, the supply of cold water to the heat exchanger causes a sharp drop in the temperature of the chimney walls. This inevitably leads to condensation of moisture from the exhaust gases on the walls of the chimney, and, as a result, the channel quickly fills with smoke and ash. To cope with this, it is necessary to reduce the heat transfer rate and temperature difference.

Along with high performance, durability is very difficult to achieve. On the one hand, an increase in the contact area between the heat exchanger and the chimney increases the heat output, on the other hand, excessive heat intake threatens big problems up to the complete failure of the chimney.

Optimal characteristics of a heat exchanger for a chimney:

1. The water circuit must be supplied with a separate heat storage tank, excluding the supply of cold water directly to the heat exchanger.
2. The heat exchanger design must be easily removable for cleaning and maintenance.
3. The power of the heat exchanger is selected based on the actual performance of the stove and chimney so that the temperature of the gases above the heat exchanger is sufficient to maintain draft.

It is better to choose stainless steel as materials for the heat exchanger, which can withstand sudden temperature changes. The internal surface of the heat exchanger in contact with the smoke should, if possible, be perfectly smooth, so that condensation, even when it appears, falls into the condensate collector without creating unnecessary problems.

Homemade heat exchangers for a chimney are often assembled without taking these requirements into account and without preliminary calculations, which causes a lot of problems, both with heating the water and the condition of the chimney.

With air heat exchangers everything is simpler. If you do not supply a large volume of cold air from the street, but use it to heat the internal volume of the room, then the temperature difference will not be sufficient for active condensation.

For heating

For organizing water heating in a house, a chimney heat exchanger will be an excellent solution, but only if there is a heat storage tank. To heat a house, there is no need to constantly heat cold water; the coolant in the system loses 20-25°C after passing through the circuit and that’s all. Accordingly, the risk of condensation forming on the surface of the chimney is reduced.

The simplest version of the heat exchanger is a coil made of a copper tube, twisted in a spiral around the chimney. The length of the tube should not be too long, even taking into account the route to the boiler and back, and depends on its diameter. If we take, for example, a size of ¼ inch, then it is advisable to limit the length to 3.5-4 meters. This way it will be possible to ensure normal heat exchange with natural circulation of water in the “heat exchanger - storage tank” circuit.

If it is not possible to install the boiler close to the stove, then it is better to use a circulation pump and force water through the heat exchanger, then the length of the tube no longer matters much. There is no need to use soldering or improve the contact between the coil and the chimney in any way. Too good heat transfer will be more detrimental.

Greater heat transfer is achieved by a water jacket, a design in which an external cylinder is installed on top of the chimney section, and water is poured between them. The chimney section can be replaced with an assembly of pipes of smaller diameter, for example 5-6 pieces, so that their total cross-section is equal to the chimney channel or slightly larger than it.

The main difficulty lies in determining the heat transfer power. The actual value is obtained only in practice, and this option will suit few people. It can be approximately calculated based on the temperature of the hot gases at the furnace outlet and the passage of the heat exchanger. The specific heat capacity of the exhaust hot gases is approximately 1.042 kJ/kg*K, slightly higher than air saturated with water vapor. Depending on the temperature difference at the inlet and outlet of the heat exchanger and the contact area, the power is calculated.

The specific heat capacity of water is 4.183 kJ/kg*K. Let’s assume a temperature difference of 150 degrees, then for every kilogram of smoke coming out you can heat a kilogram or liter of water by 38°C. Next comes the calculation of the volume of passing gases and the efficiency of the heat exchanger, which, in fact, does not exceed 60%.

To heat a small room, one chimney heat exchanger will be sufficient, but it is better to use it as an auxiliary heat source in addition to the main water circuit or hot water boiler, increasing the overall heat output.

In practice, it is easier to heat a small house or a neighboring room using an air heat exchanger for a chimney. It uses the same principle as a water jacket, only gas from the stove is released into the space between the group of pipes, and the structure itself is oriented perpendicular to the chimney. It turns out that the smoke flows around the heat exchanger tubes and heats the air in them; then, through forced ventilation, it is supplied through the air duct to other rooms of the house.

For sauna stove

In a bathhouse, using heat from the chimney is only relevant for hot water supply or using air heating. An air heat exchanger will be relevant primarily for warming up the dressing room and dressing room and other bath rooms, except for the steam room, where there is already enough heat from the heater itself.

The DHW circuit is relevant for a separate bathhouse building. It is enough to install a small container under the ceiling in the room next to the steam room and use a heat exchanger to heat the water in it.

Mounting a heating circuit based on a heat exchanger for a chimney is, to say the least, not relevant. By definition, it is too high to ensure natural circulation, and installing a circulation pump and, accordingly, cooling the chimney walls will affect the draft. Everything depends on the increased heat capacity of any, even the most primitive water heating circuit.

Flaws

The main difficulty with chimney heat exchangers is the lack of adequate power control; there are no well-established ways to stop heating the coolant or hot water while the stove is operating. If you simply shut off the water circuit, the residue in the heat exchanger can boil and rupture the chimney and the body of the device. The liquid must be completely drained.

You can somehow limit the power using dampers, but then the draft and the adjusted operation of the stove itself will suffer. The bypass path, actually a bypass, significantly complicates the design of the chimney and makes it excessively voluminous.

It all comes down to a simple idea. There is no need to put up with the loss of heat that goes into the pipe. But when installing a heat exchanger, it is worth considering that it can only play secondary roles, both in heating and in hot water supply, significantly reducing the load on the main heat source. When choosing the current model, it is necessary to carefully select the power and operating modes so as not to spoil the operating conditions of the stove itself.

Any private house, cottage, bathhouse and sometimes even a garage require heating in the winter season. But any prudent owner is faced with the question of how to reduce fuel costs and use the heating device more efficiently. One of the modern promising directions for increasing efficiency is the use of heat from hot exhaust gases.

I welcome my dear reader and bring to your attention an article about what a heat exchanger for a chimney pipe is and how to make it yourself.

Heat exchanger is a device for transferring heat from a heated medium to a colder one. One principle, many designs. A heat exchanger for a chimney allows you to select part of the energy of the exhaust gases and use it to heat an adjacent room or heat hot water.

Devices for extracting heat from flue gases for a chimney can only be used if the pipe is made of steel. It is not possible to install a heat exchanger on modern ceramic and sandwich structures, since the outer surface of the insulated pipe is cold.

The gases coming from modern gas and pellet boilers are not hot – about 200 °C, so you won’t be able to get a lot of heat from the chimney. Solid fuel boilers emit hotter gases - up to 600 °C, and the recuperator allows you to obtain a fairly significant amount of heat for heating or heating water.

The maximum amount of heat from exhaust gases can be obtained by using not very modern traditional stoves, fireplaces, and homemade potbelly stoves. The efficiency of these heating devices is low, the temperature of the flue gases is high, so a considerable part of the wasted heat can be captured using a heat sink. The use of heat collectors on the chimney of a homemade potbelly stove allows you to capture up to 30-40% additional energy.

The main reason for installing a heat exchanger is that it allows you to maximize the use of fuel combustion energy and save on heating costs. In addition, sometimes when heating small houses it is not economically feasible to purchase a heating device with a heat exchanger and install a heating system.

A modern fireplace or stove heats well houses with an area of ​​up to 70 m² and even more; only some rooms need heating - bathrooms or back bedrooms, second floor rooms or attics, so for their heating you can use the heat from the recuperator for the chimney. Sometimes a chimney heat exchanger is used to heat water.

Principle of operation

The operating principle of a heat exchanger for chimneys is heat recovery through a heat-conducting wall. In this case, the coolants move in one or different directions. In a counterflow design, coolants move in opposite or perpendicular directions, in a direct flow design - in parallel.

Types and designs

Heat exchangers are primarily divided according to the coolant into air and liquid (water). In principle, it is allowed to fill in oil and antifreeze, but not in homemade designs, since antifreeze is poisonous and expensive, and the oil can catch fire if leaks occur.

By design, water devices are usually made in the form of a coil or register (pipe) with water (water jacket); air ones are a cap with warm air removal or a wide insert into the chimney with welded transverse elements.

When deciding how to remove the residual heat of flue gases, you should keep in mind that condensation may fall on the heated walls of the chimney. This drawback is especially noticeable in gas boilers, in which the temperature of the exhaust gases is low. But on inexpensive homemade stoves you can ignore condensation.

Water

The advantage of water for recovery is that it has a high heat capacity and more efficiently removes the heat from the flue gases. But water recuperators require higher quality manufacturing - the system cannot leak; When operating it, it is necessary to ensure that there is no overheating, since boiling water can rupture the pipeline.

If water structures are used in a garage, workshop, “weekend cottage,” or a free-standing bathhouse, the water will have to be drained in the winter, since frozen liquid can also rupture the pipeline.

A circuit with water is heated through the metal walls of the chimney; when heated, the water rises up, then into the batteries, cools, falls down in the battery, goes into the return line and is sucked back into the heat exchanger.

To optimize the operation of the system, an expansion tank is included in it - this reduces the possibility of boiling. Some craftsmen install a pump, which creates a complete small heating system.

Water systems are used for heating using radiators or hot water supply. A serious drawback is the inability to regulate the heating temperature of the water; if it overheats, it simply has to be drained. It is impossible to pour cold water into the system while the heating unit is running - the water can boil, rupture the pipes and damage the chimney, while condensation settles on the inner walls of the chimney pipe.

• Homemade coil

The easiest design to make. The coil is usually made from a tube that is wound in a spiral around a steel chimney. Tubes use copper, ordinary steel, stainless steel, and aluminum. Aluminum should not be used for solid fuel boilers - its melting point is 660 °C, and the temperature of the exhaust gases of solid fuel heating devices reaches 600 °C.

When winding (bending), the pipe should be filled with sand and sealed on both sides - this will avoid defects (kinks, folds, kinks). To improve the heating of the coil, there should be a small distance between the turns - up to 1 diameter.

But it is not the most durable coil material (especially galvanized carbon steel).

• Register

Register - a casing with a larger diameter than the chimney. The register is placed on top of the chimney body and welded, the ends are welded with plates with cut holes corresponding to the diameter of the chimney. A pipe is welded or screwed in at the bottom for water supply, and at the top for discharging warm water. Otherwise it is used in the same way as a coil. The casings are made not only round, but also square.

Air

This option is more suitable for local heating of premises - one room, bathroom, dressing room. Air structures are easier to assemble. Sometimes a coil or register is used, sometimes a Kuznetsov or bell-type heat exchanger is used. The coil has too much resistance from the pipe walls; it should not be too long. Because of these difficulties, it is rarely used. Air recuperators cool the chimney less, so there is less chance of condensation forming on its walls.

Sometimes they do not build complex structures, but use available materials - they weld ribs from corners or bent strips to the chimney, pipes open on both sides, attach “skirts” or strips (aluminum or thin steel) bent into a corrugated structure.

• Kuznetsov heat exchanger

The Kuznetsov heat exchanger is an expanded cylinder, across which pipes are welded. The cylinder is mounted in the chimney, hot flue gases flow through the inside and heat the transverse elements. The air from the cavities exits into the room and heats it or is collected in an air duct and enters the adjacent room.

• Bell type

If a small house does not have a heating system and there is a need to heat a room in the attic or second floor, a bell-type heat exchanger is used. A cylinder is installed around the chimney, open at the bottom; at the top, air from the cylinder enters pipes going to the second floor. Warm air is released in the lower part of the room on the second floor - this way the hot air is better distributed in the room and heats it as much as possible.

Sometimes, instead of a cylinder above the stove, a hood is installed under the ceiling; air heated by the stove rises into it and flows through pipes into the room on the second floor. You can install a fan, in which case it is easier to heat the room on the same floor with the stove with warm air.

Which type is better

Which type is better is determined by what exactly needs to be heated and in what way. The efficiency is better for water recuperators - 50-60% (for a register parameter it is higher, for a coil it is lower). Air devices have lower efficiency.

For hot water supply or radiator heating systems, it is better to install water heat exchangers. Air heaters are more suitable for heating closely spaced individual rooms.

Power calculations

Independently calculate the power of the recuperator in the absence of initial data (furnace power, temperature and amount of exhaust gases per unit of time, contact area of ​​the heat exchanger and the metal of the chimney, speed of passage of air or water through the device) almost impossible. You can measure the power of an already installed heat exchanger.

Roughly, you should expect that the heat exchanger on the chimney of a solid fuel stove or fireplace will warm up a couple of small radiators, increase the temperature in the garage, or make a room in the attic or a dressing room in a bathhouse warmer.

Buy or make it yourself

If you want to increase the heat transfer from an expensive purchased boiler, it is better to buy ready-made high-quality devices - the industry produces them in a sufficient range. But if you want to modernize either your garage or increase the efficiency of a fireplace with a steel pipe in your country house, you can save a lot of money by making and installing a heat exchanger on the chimney yourself. Installing a heat exchanger by a hired specialist will cost the same as the structure itself.

The simplest option - a coil - can easily be made by a home hobbyist even without much experience, but a home craftsman with at least some welding skills can handle more complex designs.

approximate price

The cost of industrially manufactured chimney heat exchangers varies depending on the design and manufacturer.

Running heat exchanger tanks for a chimney with a diameter of 115 mm and a capacity of 6 liters cost rubles; those with a capacity of 12 liters cost rubles.

How to make your own device

It’s easy to make a simple coil yourself from a copper tube. For a chimney with a diameter of 100 mm, a copper pipe with a diameter of ¼ inch and a length of 3-4 m is suitable. Threaded fittings should be soldered to the ends of the pipe. Then the tube is filled with fine sand, twisted and wrapped around the chimney.

It is advisable to leave a small distance between the turns - then the pipe from the chimney will be heated by both heat transfer and infrared radiation. It is convenient to do this work with an assistant. The sand is then washed out of the pipe with water under pressure. Connect the pipes leading to the radiators and expansion tank.

The Kuznetsov heat exchanger is made using welding. The simplest option is to make a housing from a gas cylinder or large diameter pipe.

For manufacturing you will need the following materials:

1. Gas cylinder, large diameter pipe (300 mm) for the housing.
2. Pipe with a diameter of 32 mm (it is better to take one piece with a larger diameter - up to 57 mm). The length of the blanks is 300-400 mm, the total quantity should be sufficient for cutting the blanks.
3. Two small pipes of the same diameter as the chimney; It is advisable to use a chimney pipe - if the chimney is prefabricated, then on one side of the structure the pipe will have a socket, which is necessary for installing the heat exchanger.
4. Two pieces of steel sheet, sufficient to cut out the end caps of the housing.

Air heat exchanger manufacturing technology:

1. A large pipe or cylinder is cut to the required size.
2. 9 blanks of the same length are cut from thin pipes.
3. Circles are cut out for the plugs.
4. 9 holes for small diameter pipes are cut in the circles; if one tube of larger diameter is taken, then a hole for it is cut in the center.
5. Thin pipes are inserted into the holes of the plugs, attached by welding, and then welded.

Holes with a diameter equal to the diameter of the chimney are cut in the sides of the body.

A structure of thin tubes and plugs is inserted into the body and welded at the junction of the plugs and the body of a large pipe.

The pipes are inserted into the holes on the sides of the body and also boiled.

Alternative option:

What materials can be used

Perfect option - stainless steel(for example, food grade austenitic stainless steel 08Х18Н10 or AISI 304) or copper. Industrially produced products are sometimes made from titanium. But the price of these materials is quite high. But they are durable, do not rust, are reliable and durable. If you have a potbelly stove in the garage or a homemade heater from scrap materials in the bathhouse, it is quite possible to use ferrous metal (carbon steel).

You can use a high-quality corrugated stainless steel pipe. Galvanized corrugation is an undesirable and short-lived option. Aluminum pipes can also be used for the coil (just not for chimneys of solid fuel stoves).

But it should be borne in mind that during welding work the zinc layer evaporates, and all the advantages of galvanizing (corrosion resistance) come to naught. At temperatures above 400 °C, zinc begins to evaporate (zinc vapor is toxic), so you should not use galvanization for heat exchangers on the chimneys of solid fuel boilers.

Russian people do not like to lose in anything: neither in money, nor in comfort, nor in warmth. And therefore, at dachas, and in private houses, and in greenhouses, and in bathhouses, you can often see quite interesting devices from neighbors “for the sake of saving money.” And in the same way, folk craftsmen did not ignore the completely unnecessary heat that sometimes mediocrely escapes from the steam room, installing a heat exchanger on the chimney, and not on the stove or wall. And indeed, this turns out to be very profitable: why take away valuable heat from the stove if we sometimes don’t know how to cool a hot chimney pipe at least a little? But a water or air heat exchanger for the chimney is an excellent solution!

What metal is best to make a heat exchanger from?

It is better to install the exchanger itself on the pipe from food grade stainless steel. It is also called austenitic. Even at high temperatures, its characteristics do not change - after all, its welds are strong and not susceptible to cracking, and nickel reacts with oxygen on the surface to form a special protective film that is resistant to salts and acids. This is the most durable option.

As for zinc, already at a temperature of 200°C it will begin to evaporate, and at 500°C its concentration in the air will reach a dangerous value. Therefore, if you have hung a galvanized profile on the heat exchanger, but it does not heat up more than 200°C, you don’t have to worry. But you can install it - this profile serves well to enhance the convection of air that flows around the heat exchanger. Of course, such a heat exchanger is not suitable for constant heating of a house, but for quickly warming up an attic, for example, this is what you need! Those. you arrived with friends at the bathhouse, started to light the stove, and in just half an hour it was already warm in the attic or recreation room. And you don’t need to think about either the boiler or the second oven.

Installing a heat exchanger on a chimney with your own hands is quite simple. It can be attached to an ordinary iron stove, and even then covered with brick, just like a stove. It is also possible to lay the brick itself on its edge - the structure will still be stable.

For example, here's how to make a heat exchanger for a potbelly stove:

Options for connecting structures

The heat exchanger on the chimney can operate in two main modes. And each of them has its own process of heat transfer from smoke to the inner pipe of the heat exchanger.

So, in the first mode, we connect a remote tank with cold water to the heat exchanger. Then water condenses on the inner pipe, causing the heat exchanger itself to heat up solely due to the heat of condensation of water vapor from the flue gases. In this case, the temperature on the pipe wall will not exceed 100°C. And the water in the tank will take a long time to heat up.

In the second mode, condensation of water vapor on the inner wall of the heat exchanger does not occur. Here the heat flow through the pipe is more significant, and the water heats up quickly. To more fully understand this process, conduct this experiment: place a pan of cold water on a gas burner. It will be clearly visible how condensation will appear on the walls of the pan and it will begin to drip onto the stove. And despite the flame being 100°C, this state will continue for a long time until the water in the pan itself warms up. Therefore, if you use a heat exchanger on a pipe as a register for heating water, then give preference to small designs with thick walls of the inner pipe - this way there will be much less condensation.

Pipe on tin - simple and durable!

This option is simple, practical and convenient. In fact, here the chimney is simply wrapped around a metal or copper pipe, it is constantly heated, and the air distilled through it quickly becomes warm.

You can weld the spiral to your chimney using an argon torch or semi-automatic welding. You can also solder with tin - if only you degrease it with phosphoric acid in advance. The heat exchanger will hold on to it especially tightly - after all, samovars are soldered with tin and last a really long time.

Corrugation - cheap and cheerful

This is the simplest and lowest-budget option. We take three aluminum corrugations and wrap them around the chimney in the attic or second floor. The air will be heated in the pipes from the chimney walls, and it can be redirected to any other room. Even a fairly large room will be heated to hot temperatures while you heat the steam room stove. To make heat removal more efficient, wrap the corrugated spirals with regular food foil.

Heat exchanger-hood - for warming up the attic

Also, in the chimney section in the attic room, you can install a heat exchanger that would work on the principle of a bell-type stove - this is when hot air rises up, and cools down slowly. This design has its own huge advantage - an ordinary metal chimney on the second floor usually becomes so hot that it cannot be touched, and such a heat exchanger will significantly reduce the risk of fire or accidental burns.

Some craftsmen also cover such heat exchangers with a mesh with stones to accumulate heat and decorate the heat exchanger stand. In this case, the attic becomes even more comfortable and can be used as a living space. After all, based on practice, the temperature of the sauna stove pipe does not exceed 160-170 °C if there is a heat exchanger on it. And the highest temperature will already be located only in the gate area. Warm and safe!

Eco-friendly homestead: One of the most affordable ways to save heat in a stove-heated house is a heat exchanger for the chimney pipe, and it is this device that we would like to talk about in this article.

Saving and frugality are qualities inherent only to humans; they are the ones who have been driving technological progress for centuries, creating devices designed not only to make life easier, but also to use all available resources to the maximum.

Homemade heat exchanger in the form of an expansion tank.

If we concern the household, or more precisely, the communal sphere, then the costs of heating a house are rightfully considered the highest, but here too, progress and people's ingenuity have found their application.

Why is it needed?

Heat loss in the house

The photo above shows that approximately 14% of the heat that could be stored in the house is lost through the chimney. Of course, this is not the largest figure, but if you convert the losses into kilowatts of energy and multiply by the number of days during which heating was carried out, the result is quite significant.

The main purpose of the chimney pipe is, of course, to remove exhaust gases. They are the ones who heat the pipe to enormous temperatures.

Stove and chimney through a thermal imager

If you look at the stove through a thermal imager, you can see that the temperature of the chimney can be the same as in the firebox itself. The problem is that the heat transfer from the chimney is not accumulated in any way, but it can be put to use. And how to do this will be discussed below.

Types of heat exchangers

The main task of the heat exchanger is to transfer the heat emitted by the chimney over a distance, but not to over-cool its surface, as this will lead to increased formation of condensation and, accordingly, the accumulation of soot on the inside of the pipe.

It is maintaining this balance that is the most significant difficulty, especially if you decide to make a heat exchanger for the chimney with your own hands.

According to their design features, heat exchangers can be of two types:

1. Water, when heat is transferred through the natural circulation of liquid in a closed system.
2. Air, when heated air is forcibly transferred in the desired direction.

The choice of design directly depends on the individual characteristics of the house and the stove, as well as on the goals pursued by its installation. But first things first.

Closed type water heat exchanger

The operating principle of all closed heating systems is based on the elementary laws of physics - when heated, the density of water decreases and is pushed from below by colder water, it begins to rise through the pipe, entering the expansion tank, and from there it returns to the heater along the entire circuit.

In this case, the chimney acts as a heater, which with its energy pushes water along the contour of the heating system.

Homemade coil

Homemade water heat exchanger

The design shown in the photo is the most common and simplest way to use heat from a chimney. The upper edge of the tube is connected to the expansion tank, and the lower edge to the heating circuit.

Advice! Copper tube is best suited for the coil. It is easily screwed onto the chimney and has a high thermal conductivity coefficient.

Most often, such a system is used as an auxiliary one. With its help, you can heat small rooms in which heating was not previously provided, but nothing more. It will not be able to act as the main heating, since its design has several significant disadvantages:

• The temperature on the surface of the chimney is an unstable and difficult to control value, as a result, it is impossible to regulate the degree of heating of the coolant.
• Due to the variability of temperature, it is very difficult to calculate the optimal coil length. If it is too short, the water will begin to boil and rupture the tube, and if it is too long, the coolant will not warm up to the desired temperature at all.
• The water from the expansion tank cannot be used for showering or other purposes, and this is not just due to unregulated heating. When the tank is filled with cold water, it will begin to cool the chimney through the coil, resulting in the formation of condensation and accelerating the process of soot formation on the internal walls.
• The temperature to which the chimney heats up is not enough to warm up a long circuit. With conventional heating, water passing through the system loses only 25 degrees; to maintain this figure in this situation, the entire system must be small in size.

Important! Some “folk craftsmen” come up with the idea that heat exchanger in the chimney will be much more effective, because the temperature there is higher. This should not be done under any circumstances; foreign objects inside the pipe prevent the free passage of gases, as a result of which they can enter the room.

Register heat exchanger

Factory heat exchanger

To avoid problems with homemade devices, you can purchase a register heat exchanger for the chimney pipe. Of course, the price of such a device will be higher than that of a DIY one. But the quality characteristics cannot be compared.

The principle of operation of such a device is identical to that described above, with the only difference being that all the calculations have already been made to protect the device from boiling. Unfortunately, there is no heating control here either, but there are several significant advantages compared to “homemade” ones:

• The outer casing retains heat inside, allowing the coil to warm up even at low chimney temperatures;
• Copper tubes do not come into close contact with the heating surface, this protects the device from possible boiling.

Internal structure of the heat exchanger

Important! Each factory heat exchanger comes with detailed installation instructions. To achieve maximum performance and not encounter unexpected problems, you must study it carefully and follow all the manufacturer’s recommendations.

Air heat exchangers

Air heat exchanger

The principle of operation of such a device is that hot gases inside the chimney flow around the heat exchanger tubes, due to which they heat up and release energy outside. In fact, it does not create additional heat, but simply directs hot air into the air in a given direction.

The air heat exchanger for the chimney can be either independent or with forced draft. To speed up the spread of hot air in the room, a regular fan is often used; this is quite enough to circulate the air, and at the same time does not over-cool the chimney.

You can assemble such a heat exchanger yourself, and all stages are shown in the video in this article

Heat exchanger "Kuznetsov"

Kuznetsov heat exchanger design

This is the most optimal chimney heat exchanger for heating a cold attic or attic. Hot gases always tend upward, and since the outlet is located below the inlet level, they first heat the heat exchanger, and after that, when they cool down, they enter the pipe, from where they go outside.

A chimney with a Kuznetsov heat exchanger will not be able to completely heat the room, but it almost completely eliminates heat loss, releasing only cooled gases through the pipe. published

If you have any questions on this topic, ask them to the experts and readers of our project.