Types and rules for mounting heat exchangers on a chimney pipe

A stove used for heating a house or cooking food can be converted with your own hands into a unit that will heat water for domestic needs. To do this, it is necessary to mount a heat exchanger on the chimney pipe. How to do this, we will consider in the article.

What is a heat exchanger

This is a technical device made of a material with a high thermal conductivity, in which two media with different temperatures come into contact through a partition. It is through the wall of the device from one medium that the temperature is transferred to another.

There are two types of heat exchangers:

1. Recuperators. That is, those in which the temperature transfer occurs through the partition.
2. Regenerators. In them, media with different temperatures are in contact with a single surface in turn.

There are several types of heat exchangers that differ from each other in a purely constructive design. These are the commonly used options:

1. A coil is a tube wound around a chimney through which water moves.
2. Pipe in a pipe. This is a cylinder-shaped structure mounted on a chimney. Water flows inside it, which enters the structure through the lower pipe, and exits through the pipe installed at the top of the heat exchanger. The heating of the liquid occurs through the wall of the chimney.
3. Spiral. They are rarely used in everyday life, because structurally it is a container into which a pipe is laid in a spiral (along the inner walls), a hot medium moves inside. Unfortunately, the chimney will not work in this form.
4. Shell and tube. This is not a home appliance. Its design is a container in which a large number of tubes are inserted. A medium with a high temperature moves along them, and water moves between the tubes.
5. Lamellar, they are also called convectors. This model is the same as the previous one. Only in it, instead of tubes, hollow panels are installed, along which a medium with a high temperature moves. And between them is water. The efficiency of thermal energy transfer here depends on the direction in which the media move relative to each other. Optimally — towards each other.

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There is another classification in which heat exchangers are divided into water and air. The first has been written above. As for the latter, with their help, they mainly organize additional heating of the premises. A prominent representative of such units is corrugated heat exchangers.

To do this, use steel corrugated pipes (they are flexible), which wrap around the chimney. It turns out that high-temperature carbon monoxide gases coming from the furnace furnace give off part of the heat to the air passing inside the corrugation. The latter is connected to the street, usually it is introduced into the room through a hole located close to the floor. Sometimes a low-power fan is installed to give the air a low speed. The opposite end of the corrugation is installed in the room where you want to raise the temperature.

Materials for heat exchangers

Usually the chimney is assembled from metal pipes. Rarely, ceramic or glass chimneys are installed in the steam room of a bathhouse or other rooms other than the main house. Too expensive. Therefore, we can safely say that these structures have a high thermal efficiency. Therefore, a heat exchanger can be mounted on them.

The material for the heat exchanger itself is selected to withstand large thermal loads, because the temperature of carbon monoxide can reach up to +500C. Plus, it is necessary to take into account the negative effect of water on the metal. Therefore, coil tubes must be made of either copper alloy or stainless steel.

If it is decided to build a pipe-in-pipe heat exchanger, then for its manufacture it is better to use a stainless steel or galvanized structure.

How to install a chimney coil

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This twisted design is considered the simplest. It is direct-flow, so much will depend on the diameter of the coiled tube and the speed of water movement inside it. Here the ratios are:

• The larger the diameter of the coil, the greater the volume of water in it, which will take longer to heat.
• The faster the water moves along the coils, the less heat energy it takes, simply not having time.

There are two ways to solve these two problems:

1. Increase the length of the pipe twisted into a coil. That is, water should be inside the heat exchanger as long as possible.
2. Install a shut-off valve in front of the coil, with which it would be possible to control the flow of liquid. In this way, you can increase or decrease the speed of water movement.

Installation of this type of water heat exchanger is carried out at the stage of installing the chimney. Because it is necessary to insert chimney pipes into the coil.

This will require:

• a pipe made of copper, aluminum or steel, 3 m long;
• two flexible hoses for connection to the hot water supply system, of the required length;
• valve.

The most difficult thing is to bend the pipe into a coil. If this steel product is less than 25 mm in diameter, then it can be bent on a manual pipe bender. If the diameter is greater than this value, or an aluminum or copper pipe is used, then they cannot be dispensed with without heating. For this, a standard propane gas burner is used.

There is another way, which is practically not used today. To do this, fine sifted sand is poured into the pipe, it is closed with plugs on both sides, and then it is bent along a pipe with a diameter of 100, 120 or 150 mm. That is, corresponding to the size of the chimney. After the finished structure is freed from the filler and washed under the pressure of water.

The next step is threading the end of the coil. To do this, use a lerk. If the heat exchanger is made of a steel pipe, then the ends can be welded to the ends by electric welding with spurs with the appropriate diameter for flexible adapter hoses.

Everything is ready, you can mount the heat exchanger. To prevent it from falling off the chimney, you can attach it to it using soldering. This will increase the heat transfer between the two elements. Further, a valve is screwed in the lower part, a flexible insert is attached to it, which is connected to the water supply system at the opposite end.

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The free upper end of the heat exchange unit is connected either to a storage tank or to a tap. A flexible connector is used for connection.

Heat exchangers of this type have one serious drawback. If it is not used when the stove is in operation, the water inside the tubes will boil. And this is not far from the water hammer, which can break the joints of the joints.

How to install a pipe-in-pipe heat exchanger on a chimney

Purely structurally, this type of heat exchanger is a tank in which a pipe with a diameter slightly larger than the diameter of the chimney is installed. For example, if the size of the latter is 115 mm, then the pipe section should be 120 mm in cross section. That is, the chimney must pass freely through the heat exchanger.

You can approach the solution of installing a heat exchanger from the other side. That is, the diameters of two tubular elements are selected with the same section. But they must be connected in a bell-shaped way, like all elements of the chimney system. This is when one end of a section of a pipe element has a standard diameter, and the other is slightly expanded.

That is, it turns out that the pipe that forms the through passage through the water tank becomes part of the chimney after assembly. This option is more efficient in terms of transferring thermal energy from carbon monoxide to water, because there is no air gap in the design of the heat exchanger, as in the first case.

As for the size and shape of the tank, the first is the diameter, which should be 1.5-2.0 times larger than the diameter of the chimney structure. The length in this regard depends on the need for water. But it is limited by the length of the chimney. The shape of the tank may be different. But more often they use a cylindrical or in the form of a straight parallelepiped. Although there are also very unusual forms.

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Note that water tanks installed on chimneys are now sold ready-made, but they are easy to make with your own hands. To do this, you need to have skills in working with a welding machine and some types of metalwork tools. It’s easier to purchase a finished product of a certain volume, in which a pipe for a chimney of the required section is already installed. There are also pipes (fittings) for the supply and output of water.

The assembly of the entire structure is based on the creation of tight joints. Therefore, the joints must be coated with heat-resistant sealants.

After installing the coolant, it remains only to connect it through the valve to the water supply network, and on the other hand to the storage tank or tap (mixer). Connections are made with flexible connectors or pipes of the appropriate diameter.

Important! This type of heat exchanger must be filled with water before operation. If you start kindling without it, then it is likely that the metal will lead, and this will lead to depressurization of the joints of the parts.

Conclusion on the topic

A heat exchanger installed on the chimney of the furnace is a real opportunity to save on the organization of hot water supply. It is important to correctly carry out the installation, taking into account the requirements of fire safety.