To heat water in an indirect heating boiler, you can use a gas or solid fuel boiler, a solar water heater or a heat pump. In this case, the operation of an instantaneous water heater of this type is possible both in conjunction with a single-circuit and with a double-circuit heating unit. WITH circuit for connecting an indirect heating boiler differs depending on the type of boiler and the selected hot water supply method.

The piping of the water heater requires its connection to the heating system, as well as to the cold and hot water supply lines. In this case, cold water enters from below, hot water is discharged from the top of the tank, and the recirculation point is located approximately in the middle of the boiler.

The heated coolant should move the other way around - from top to bottom.

The coolant from the boiler enters the upper branch pipe of the water heater, and returns to the heating main from the lower branch pipe of the boiler.

Thus, the efficiency of the device is increased by transferring heat first to the most heated layers of water.

To properly connect the boiler, you need to know the basic methods of connecting it.

Connecting a wall-mounted boiler to a heating unit

Connecting a boiler to a gas boiler

To connect an indirect heating boiler to a gas heating boiler, its design provides for a temperature sensor installed in the tank.

Connection to a double-circuit boiler

To operate the boiler in tandem with a heating unit, which has a hot water supply circuit, a three-way valve is used. With its help, the flow of the heated heat carrier is distributed between the main heating circuit and the additional hot water supply circuit.

The three-way valve is controlled by signals that come from a thermostat installed in the water heater. When the water in the boiler is cooled below the set value, the thermostat turns on the valve, which directs the flow of the heating medium from the heating pipe to the hot water supply circuit. The thermostat switches the valve to its initial state when the water temperature in the tank reaches above the set value. In this case, the flow of the coolant is directed to the heating main. In the warm season, the flow is not redirected, but the boiler combustion mode is controlled. When the water temperature in the boiler drops, the thermostat, by means of a three-way valve, "ignites" the main burner of the unit, and when it rises, the gas supply to the burner stops.

Connecting the boiler to the boiler using a three-way valve

This connection diagram is perfect for gas boilers equipped with a circulation pump and automation. In this case, the valve can be controlled by the boiler itself on the command received from the water heater thermostat.

In a connection diagram with a three-way valve, the cylinder circuit has priority over the heating circuit. The use of this method of connecting the boiler is justified for large tanks or with high water hardness, which will not allow the DHW circuit to work normally.

When setting the maximum water temperature in the boiler (thermostat response temperature), it should be borne in mind that it must be lower than the temperature set for the boiler automation.

Connection to a single-circuit heating unit

When connecting the water heater to a single-circuit boiler, a circuit with two circulation pumps is used. This type of connection can actually replace a circuit with a three-way sensor. A feature of this connection is the separation of the coolant flows through different pipelines using pumps. The hot water supply circuit also has a higher priority over the heating circuit, however, it is achieved only by setting the switching algorithm. Therefore, it is more correct to talk about the parallel operation of both circuits.

Alternating switching on of centrifugal pumps is also carried out by signals from a thermostat installed in the tank.

To exclude mixing of the heat carrier flows, a check valve must be installed in front of each pump.

Boiler installation diagram in a system with two circulation pumps

Operation according to this scheme is similar to the previous case, with the only difference that the thermostat controls the alternating operation of two pumps. When the DHW pump is turned on, the heating pump is turned off, therefore, the heating system begins to cool down. However, the short heating time of the water in the boiler does not lead to a noticeable decrease in the indoor temperature and can be felt only during the initial start-up.

Sometimes several heating units are used to heat large houses. In this case, an additional pump is installed to ensure the operation of the water heater.

Scheme using a hydrocollector

The use of a hydrocollector in heating systems with several circuits

In complex multi-circuit heating systems, there are several circulation pumps responsible for ensuring the operation of individual circuits. In order to balance the flows of the coolant from different pumps, a hydraulic distributor or manifold is used. This device allows you to compensate for pressure differences in various circuits and branches of the heating system. Without a hydrocollector, balancing valves would have to be used, which greatly complicates the setup and operation of the heating system and the arrangement of hot water supply.

When using an indirect heating boiler in such a system, additionally consult with practitioners.

By connecting a storage water heater to a solid fuel boiler, they achieve two goals at once - they connect the hot water supply and get a system for emergency discharge of the coolant. The fact is that in systems with solid fuel boilers, thermostatic valves are often installed on radiators in order to increase comfort. However, in this case, the boiler may overheat. The same threat is real and with unstable power supply for systems with forced circulation of the coolant.

In the case of installing a high-capacity boiler, this process is not scary, since the excess heat is used to heat the water in the water heater tank. Of course, for such a system to function, it is necessary to install a natural circulation boiler.

Diagram of connecting an indirect heating boiler to a solid fuel boiler

Solid fuel boiler safety group.

1. Expansion tank.
2. Boiler safety group.
3. Hot water pipeline.
4. Shut-off valve on the flow line.
5. Heating pump.
6. Water heater pump.
7. Check Valve.
8. Shut-off valve.
9. Drain valve.
10. Solid fuel boiler.
11. Boiler shut-off valve.

To close the natural circulation branch during pump operation, a check valve is installed at the outlet pipe of the water heater. When the pump is turned off, the valve opens, which allows the heat to be dumped into the boiler.

The non-return valve is an important element of the system

The boiler, which has a recirculation line inlet, allows instant hot water supply. At the same time, by opening the tap, there is no need to drain cold water from the "hot" pipeline.

This is possible thanks to the use of a separate looped circuit with its own circulation pump. Such a circuit is called a recirculation system. A heated towel rail can be additionally installed in this line.

Diagram of a boiler included in the recirculation system

In the piping of the boiler included in the recirculation system, the following are used:

• Check valve - to prevent mixing of hot and cold water flow.
• Air vent - to prevent air from entering the system when the pump is turned on.
• Safety valve - serves for emergency pressure relief.
• Expansion tank - compensates for the thermal expansion of the coolant when the taps are closed.

The pressure in the expansion vessel must not exceed the response pressure of the safety valve.

Installation errors

During installation or during the operation of the boiler, typical mistakes must be avoided:

• Installation of the boiler at a considerable distance from the boiler. It is necessary not only to install the water heater as close to the heating unit as possible, but also to correctly orient its pipes relative to the pipelines to facilitate installation.
• Incorrect connection of the heating medium inlet and pressure pipe. The heating medium is always supplied to the upper part of the boiler, and cold water to the lower branch pipe.
• Incorrect installation of the circulation pump. The pump should be oriented according to the manufacturer's instructions.

Installation carried out in accordance with all the rules will not only ensure reliable hot water supply at any time of the year, but will also enable the boiler to work in a more gentle, economical mode.

Video. Connecting an indirect heating boiler to a gas boiler

An indirect heating boiler is installed in conjunction with single-circuit gas and solid fuel boilers, heat pumps, solar collectors. For normal operation of the water heater, a piping made in accordance with the manufacturer's manual is required.

Connecting an indirect heating boiler to a single-circuit boiler requires special skills, a clear understanding of the internal structure of the storage tank. There are several options for strapping, which makes it possible to take into account the technical conditions of the BKN operation.

Fittings for strapping BKN

The principle of operation of the boiler is associated with the use of heat taken from the heating system for heating DHW. The BKN strapping should solve several important tasks:

1. ensure continuous circulation of the coolant from the boiler to the water heater;
2. prevent hydraulic and thermal shock;
3. maintain the set temperature of water heating in automatic mode.

When installing the boiler, the following shut-off and control valves are used:

• Diaphragm expansion tank- designed to compensate for thermal expansion in the hot water supply system and prevent emergencies. When connected, the BKN is installed together with the safety group. The expansion tank must hold at least 10% of the total volume of the indirect heating boiler.
• Safety valve- needed for emergency drainage of water from the BKN. If the pressure rises too high, it opens and releases water from the boiler. The valve is used during service to fill the accumulator with chemical reagents that remove scale.
• Indirect heating boiler safety group- includes a pressure gauge, a relief valve and an air vent. The unit is designed to normalize the pressure in the hot water supply and prevent water hammer. Installation of a safety group and an expansion tank is a requirement imposed by manufacturers on the BKN piping.
• Boiler temperature sensor- connected to a circulation pump that controls the pressure in the coil. The immersion thermostat works according to the relay principle. When sufficient water heating is achieved, the sensor gives a signal to turn off the pumping equipment. The water stops heating up. After cooling down, the boiler automation starts circulation.
• Three-way valve- works as a mixing unit, opening and closing the water supply to the boiler from the heating system. There are simple mechanical devices and precision servo driven 3-way valves.
• Circulation pump- depending on the selected piping scheme, one or two modules are installed. The pump is used to create constant pressure and recirculation in the DHW system.

The connection set may vary depending on technical conditions, building characteristics, actual demand for hot water and other parameters. Additional equipment may be present in the piping: hydraulic switch, filtration system.

BKN piping material

Cold and hot water supply, supply and return of the heating system are connected to the boiler. The heating temperature and pressure on the pipes determine which material is preferable to use when performing piping:

• Cold water - a regular polypropylene pipe can be installed. The material is suitable for brazing the entire cold water system.
• Hot water supply- DHW temperature supplied to the user is maintained at 65-70 °. It is allowed to use polypropylene with fiberglass (reinforced) or aluminum reinforcement, intended for hot water supply.
  Another option is to use a copper pipe strapping. When laying with a copper pipe, it is imperative to use thermal insulation. Copper is a good heat conductor, which will inevitably lead to a decrease in the temperature of the heated water during transportation to the end consumer. Thermal insulation of pipes will protect against heat loss.

An alternative to polypropylene can be a metal-plastic pipe. The material can withstand high pressure and heat up to 95 ° C. Fitted with crimp and press fittings.

The installation site of the boiler is immediately behind the heating boiler, in front of radiators and underfloor heating. This connection scheme is due to the fact that in order to heat the hot water supply, the coolant must be heated to 90-95 ° C. A serious heat load is observed in the area between the boiler and the boiler. It is recommended that this piping section be made with steel or copper pipes.

Options for piping an indirect heating boiler

Several conditions affect the choice of the connection scheme. What matters is the heat source, the number of draw-off points, the presence of underfloor heating, heating radiators in the system. The piping methods are selected individually in each case, with an emphasis on the technical conditions of hot water supply and heating systems.

Another important factor to consider when choosing a connection type is volatility. There are, in which the circulation of water and coolant occurs independently, as well as schemes with the creation of forced pressure (pumping). The latter cannot work without electricity. Manufacturers of BKN in the operating instructions indicate the recommended strapping scheme, which is also taken into account when connecting.

BKN piping with three-way valve

The scheme with a mixing unit - connection with DHW priority, is successfully used when several heat sources (boiler, solar collectors, heat pump) are connected to the boiler at the same time. BKN is mounted immediately after the heater. A circulation pump is cut into the supply, a three-way valve is installed.

There are several advantages of the solution:

• fast DHW heating;
• savings with constant use of the boiler;
• the ability to automate water heating.

The three-way valve redirects the supply of the heating agent from the heating system to the BKN until the temperature in the boiler reaches the set values. After DHW heating, the heat carrier is fully returned to the heating system.

Double-pump piping scheme

A good solution in cases where the boiler is planned to be used only from time to time. Requires the connection of two circulation pumps. The first is put on heating, the second directly on the water supply to the BKN. A constant circulation of the coolant in the building heating system is maintained.

The circulation pump for the storage device is connected to the temperature sensor. When the DHW heating temperature drops, a signal is given to turn on. Sufficient pressure is created to change the movement of the coolant and direct it through the BKN. In order for the system to function normally, an accurate calculation of the pump for an indirect heating boiler is needed.

Connection via a hydraulic arrow

The circuit is used for industrial purposes, as well as for piping large storage tanks over 200 liters. Connection via a hydraulic arrow is also used for branched complex heating systems: combining warm floors and radiators, a solid fuel boiler, together with solar collectors.

The strapping requires preliminary competent heat engineering calculations. The connection diagram is complex, so it is better to seek professional help for implementation.

Strapping in a gravity system

Hydraulic connection diagrams used with non-volatile heating boilers. The boiler and related equipment is raised above the boiler. The distance between the level of the heat exchangers of the boiler and the water heater must have a gap of at least 1 m in height.

The gravitational system has several disadvantages associated with the peculiarity of its work. The water heats up more slowly, the heating temperature and the water supply in the tank will be less than in systems with forced circulation. The main advantage: the ability to work in the absence of electricity. With frequent power outages in the network, the gravity system is out of competition.

Installation of DHW recirculation with BKN

In normal mode, when using hot water, a certain amount of it constantly remains in the pipeline between the BKN and the point of draw-off. In complex DHW systems, without recirculation, several tens of liters of liquid can be found in this section.

When you reopen the tap, the already cooled water first flows out of it, which reduces the comfort of using the boiler. Recirculation is needed to provide instant hot water supply to the consumer. An additional advantage is the ability to connect a heated towel rail.

The piping scheme for an indirect heating boiler with recirculation is practically no different from a conventional connection. The difference is that a tee connected to the return pipeline is installed in front of the mixer itself or the tap. The DHW recirculation line through the indirect heating boiler will operate exclusively with the use of pumping equipment.

Recirculation has several disadvantages:

• decrease in the temperature of DHW heating;
• increased fuel costs;
• volatility.

In the design of European indirect heating boilers, companies, ACV,
A common question to which there is no single answer. Connecting an indirect heating boiler to a double-circuit boiler will solve the problem of waiting: from the moment the tap is opened until the actual supply of hot water. In practice, the following happens:

• When the tap is opened, the double-circuit boiler heats up the DHW heat exchanger, spending the maximum amount of heat energy on it. The coil takes time to warm up. For this reason, hot water is supplied to the user not immediately after opening the tap, but after some time (the period depends on the distance of the draw-off point and the power of the boiler).
• Frequent starts and stops of hot water supply put a load on the heating elements, which can lead to rapid equipment failure.

According to some estimates, only 1 draw-off point with intensive use wastes about 70 liters of water. A double-circuit boiler with an indirect heating boiler in normal operation works in the same way as a single-circuit one. Heat from the heating system enters and accumulates in the storage device. When DHW is turned on, hot water is immediately supplied to the consumer. The piping of the boiler and the indirect heating boiler provides for the installation of a recirculation system.

The main disadvantage of the scheme: the dependence of the BKN operation on the boiler throughput. The parameter affects the speed of hot water preparation. Heat transfer in this case will be lower.

It is better to initially connect the BKN to a single-circuit boiler. Connection to a double-circuit boiler is ineffective and is used mainly if it is necessary to modify an existing heating and hot water supply system.

In order to always have warm water in the house, an indirect heating boiler (BKN) is installed. Installation of such a device is expedient and cost effective. During installation, it is important to pay special attention to the piping of the indirect heating boiler with recirculation in order to avoid common mistakes. You also need to learn more about how this type of equipment works.

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How the device works

Before purchasing and installing a boiler, you should understand some of the design features and the principle of operation of the most popular models. There are many types of similar installations capable of operating simultaneously from a heating system and alternative energy sources.

It is advisable to consider as an example traditional installations with a classic coil, which work (receive heat energy) from hot water. To begin with, you should understand in more detail the term "indirect heating". Classic installations use an electrical connection or natural gas to generate heat. Boilers do not have these advantages. They are connected to hot water supply and use the heat of water or other heat carrier.

DHW recirculation (boiler and DHW pump)

Standard units are in the shape of a round barrel (although more convenient and compact square models already exist today). If you look closely at the product line from well-known manufacturers, you will notice a certain trend. They all have the same design. This applies to both boilers and gas boilers. You can significantly save space when placing them by installing one unit on top of another.

The only heating element is a brass or steel coil. It is located inside the body (tank), which has a protective enamel layer. To reduce heat loss, the case is well insulated, and sometimes it is covered with a protective casing.

If you need to quickly heat water, then you should choose devices with several heat exchangers. For a slow cooling of water, models with good insulation are needed.

- one of the most important elements in modern boilers. The part serves to prevent the appearance of corrosion on all internal surfaces, and the rod itself is located inside the structure in the upper part of it. Thanks to this, the unit lasts several times longer. The design must necessarily have a thermostat and built-in valves, since they are protectors against a strong increase in pressure as a result of failure of the entire system.

A common myth says that boilers are not efficient equipment for heating water, since the temperature of the coolant in the coil does not exceed 70 ° C. This is not true. It all depends on the area of ​​contact of the coolant in the coil with water. In the BKN, it is quite large, so the water is heated efficiently even at a seemingly low temperature, not exceeding 70 ° C.

The device works very simply. The boiler tank is completely filled with cold water for heating. Inside there is a coil into which hot water from the boiler is started at this moment. Cold water heats up after a certain time and becomes suitable for taking a shower, washing dishes and other household needs.

Diagrams for connecting an indirect heating boiler to a wall-mounted single-circuit boiler



Equipment with control unit

Today there are two options for boilers - simple (cheaper) and with a built-in control unit. It should be remembered that such a unit is mandatory if the main heating device, for example, a gas boiler, does not have a control function.




A temperature sensor is often installed inside the built-in control unit. It is also possible to stop or turn on the water supply to the heat exchanger. The device can work in automatic mode. To connect the equipment, you must perform the following steps:

• connect the inlet and outlet lines for starting water from the boiler;
• connect the hose and turn on the cold water supply;
• install a collector to distribute hot water at the outlet.

Many people think that with a control unit, the temperature of the water in the boiler can be adjusted. This opinion is wrong. The maximum attainable temperature is the degree of the heat carrier itself, which is supplied directly from the boiler. Typically, the liquid will heat up 1-2 degrees less. If you need water with a higher temperature, then it is better to choose a model with a built-in heating element. Typically, such a scheme is needed in the presence of a low-temperature boiler.

It is better to buy such units together with a solid fuel boiler. Even if the wood burns out, there will always be access to hot water for a long time.

Overview of water supply with DHW recirculation



Varieties of aggregates

Tanks with the simplest design occupy only a certain part of the market for such equipment. There are more advanced models, the functions of which are very useful for combining with a DHW system. For example, there is a possibility of heat accumulation in such equipment. It is necessary in the event of frequent power outages or high electricity tariffs. Such units are distinguished by reinforced insulation, which prevents heat loss, as well as an increased volume of the storage tank up to 300 liters.

There is another option for piping a DHW boiler with recirculation, in which water is supplied to the water intake points much faster. The difference between this design is to provide the device with not one pipe for connection to the hot water supply system, but three or more. Hot water flows through two pipes, and cold water flows through the third. Circulates liquid using a pump. With such a scheme, you can implement a lot of useful ideas, for example, equip a place for drying towels. Water in such equipment heats up faster than in conventional structures, but its price is also much higher.



Optimal tank size

Cylindrical tanks have dimensions that differ from square (cubic). The dimensions of the device must be selected taking into account the installation possibilities, the availability of space and the family's needs for hot water. There are very compact models for 80-100 liters. The largest ones can be up to 1600 liters.

When installing the device, these indicators are very important. When placing the boiler on the wall, you only need to choose small models up to 150 liters. Larger devices must be installed on the floor.

All wall-mounted units are supplied with special fasteners and brackets. The outdoor equipment is equipped with legs or a special stand.

Single-circuit boiler and indirect heating boiler, how to connect?

Boiler piping

A simple piping scheme for a boiler and an indirect heating boiler assumes their joint installation along with all pumps and other equipment. It will be much easier that way. If you install the boiler in an already installed DHW network, then this is much more difficult. In order for the devices to work normally, you must adhere to some rules:






If the walls in the house are made of plasterboard or thin wood, then it is better not to buy wall-mounted boilers, since they simply will not stick to such a surface. In this case, it is better to choose floor models. For fixing wall devices, concrete or brick surfaces are more suitable.

The brackets of the wall units are fixed with dowels, brackets or anchor bolts. As a rule, they are provided by the manufacturer together with the equipment. If not, you can buy them at any hardware store.

The boiler must be installed at or above the boiler level. If everything is clear with wall models and they can be attached in any suitable place, then for floor appliances it is necessary to make a special pedestal no more than 1 meter high.

All connections should be directed towards the boiler, even if they are hidden behind the device or false wall.

Correct installation

When choosing a piping scheme for an indirect heating boiler, you should also decide on the principle of its operation. It can be with or without priority.

The first option is to prioritize water heating in the boiler. If necessary, all the coolant from the boiler can be passed through the BKN coil, as a result of which the water will heat up much faster. After the liquid is heated to the required temperature, the coolant is redirected to the radiators by switching the mode in the control unit.

If you connect the system without priority, then the entire coolant cannot be redirected. The water will take longer to heat up, since only a fraction of its volume is used.

Heating with a boiler according to the principle of priority is much more efficient than the usual one, since it makes it possible to heat a large amount of water very quickly without damage to the heating system.

When the heating is turned off, the air temperature in the room in half an hour, if it drops, is insignificant, but during this time it will be possible to get a large volume of warm water. It should be remembered that such a scheme requires a very powerful boiler.

BKN connection diagrams

Boiler connection diagrams depend on its class, manufacturer and heating system in the house. It is important to choose the right installation location. In this case, you need to take into account the location of the boiler, the pump insert and other nuances. There are such basic strapping methods:



Thus, the installation of a BKN boiler in the heating system of a private house or apartment plays an important role saving the family budget and getting hot water quickly.

Why do you need a hot water boiler for a double-circuit gas boiler or column

For heating and hot water supply (DHW) of houses and apartments, the owners often install double-circuit gas boilers or gas water heaters. A DHW system with such a boiler (column) is relatively cheap and takes up little space.

However, after a while, the owners begin to be annoyed by the shortcomings in the operation of hot water supply with a double-circuit boiler (column).

DHW flow-through heat exchanger of a double-circuit boiler (columns) begins to heat the water at the moment of the beginning of the parsing of water when the hot water tap is turned on.

All the energy spent on heating is transferred from the heater to the water almost instantly., in a very short time of movement of water through the heater. To obtain water of the required temperature in a short period of time, the design of an instantaneous water heater provides for limiting the flow rate of water. The water temperature at the outlet of the instantaneous heater is highly dependent on the water flow — the size of the stream of hot water flowing from the tap.

For heating an economy class house, a lower power boiler is usually sufficient. That's why, the power of the double-circuit boiler is chosen based on the need for hot water.

The DHW circuit with a double-circuit gas boiler or water heater cannot provide comfortable and economical use of hot water in the house for the following reasons:

• The temperature and pressure of the water in the pipes are very dependent on the amount of water flow. For this reason when opening another tap, the water temperature and pressure in the DHW system change significantly. It is very uncomfortable to use water at the same time, even in two places.
• At low hot water consumption, the instantaneous water heater does not turn on at all and does not heat the water. To obtain water at the required temperature, it is often necessary to use more water than necessary.
• At each opening of the water tap, the double-circuit boiler or the column restarts, constantly turns on and off, which reduces the resource of their work. Frequent re-ignition of the burner reduces the efficiency of the water heater and increases the gas consumption. Each time hot water appears with a delay, only after the heating mode has stabilized. Some of the water uselessly goes down the drain.
• The power of a gas boiler (column) in DHW mode is often more than required, which leads to cyclic (clockwise) heating of hot water. The boiler (column) burner in DHW mode periodically turns on and off. Accordingly, consumers hot and cold water goes, and also all the disadvantages of frequent re-ignition of the boiler burner indicated above are manifested. To eliminate stroking, the water flow rate is usually increased in excess of what is required.
• In DHW systems with a double-circuit boiler it is impossible to recirculate water in the distribution pipes around the house... The waiting time for hot water increases with the increase in the length of the pipes from the boiler to the place where the water is drawn. Part of the water at the very beginning has to be uselessly drained into the sewer. Moreover, this is water that has already been heated, but managed to cool down in the pipes.

Ultimately, the use of a double-circuit boiler (column) in the DHW system leads to an unreasonable increase in water consumption and the volume of sewage effluents, to an increase in electricity and gas consumption for heating, as well as to insufficiently comfortable use of hot water in the house.

The DHW system with a double-circuit boiler is used, despite its shortcomings, due to comparatively low cost and small size of equipment.

More economical and comfortable is the heating and hot water supply system with a single-circuit boiler and an indirect heating boiler.

But what to do if a double-circuit boiler or a column is already in the house or apartment, and the owners do not like the operation of the DHW system, and you want to get rid of its shortcomings.

Three options for connecting the boiler to a double-circuit gas boiler or column

1. There is an option to purchase indirect heating boiler, with a heat exchanger inside, and connect it to the heating circuit of a double-circuit boiler. But the cost of such a boiler and additional equipment for its connection and piping is quite high. This article is not considered this option.

2. In the DHW system with a double-circuit boiler or a column, I recommend installing layer heating boiler... In such a boiler there is no heat exchanger, which significantly reduces its cost.

3. Or, in the DHW circuit, between the double-circuit boiler (column) and hot water consumers, install electric storage water heater - boiler... This option does not eliminate all the shortcomings of the DHW system, but it can significantly improve the comfort of using water.

Connecting a storage electric hot water heater to a double-circuit gas boiler

The easiest way to improve the DHW system with a double-circuit gas boiler or water heater is to install an electric storage water heater - an electric boiler.

Wiring diagram for connecting an electric DHW boiler to a double-circuit gas boiler, as a storage buffer tank between the boiler and consumers.

An electric boiler is used as a buffer tank between the boiler and hot water consumers. From the DHW circuit of a double-circuit boiler, hot water, before reaching the consumer, enters the electric boiler. Hot water is supplied to the taps from the boiler.

Electric storage water heater - the boiler is used to store the stock of hot water heated by a gas boiler. In addition, the temperature of the water in the boiler is maintained at a predetermined level by turning on the electric heating element. The activation of the electric heater is controlled by the boiler thermostat.

In the diagram, on the water supply pipe from the boiler to the boiler, a block of two valves is installed - a check valve and a safety valve. The valves are usually sold complete with an electric boiler.

Check valve prevents water from leaving the boiler when water disappears in the water supply system.

Safety valve relieves excess pressure from the DHW system associated with the expansion of water during heating. A small amount of water periodically flows out of the valve that needs to be disposed of somewhere.

In addition, the manufacturer of the electric boiler prescribes regularly, every two weeks, to check the serviceability of the valve by manually activating it. In order to avoid these problems, I recommend additionally install an expansion tank for hot water supply, which will compensate for changes in water pressure in the DHW system.

Relief valve response pressure 6 - 8 bar, depending on the boiler model. If the water pressure in the water supply system is higher than the opening pressure of the valve, then it is necessary to install a pressure reducing valve... The valve is adjusted to reduce the outlet water pressure - not more than 80% of the pressure of the safety valve.

The DHW circuit with a gas double-circuit boiler (column) and an electric storage water heater - a boiler, is somewhat popular due to its simplicity and lower cost. There is no circulation pump in the scheme, you can use a conventional electric boiler, the number of fittings for piping is also minimal. But the operation of a DHW system with a buffer electric boiler has its drawbacks.

Advantages and disadvantages of a DHW system with a buffer electric boiler

DHW circuit with an electric buffer boiler ensures a stable water temperature at the outlet to consumers, including at low water consumption, and when the boiler is running. The water temperature in the boiler can be set above 60 o C , (temperature supplied by the boiler). Using hot water will become more comfortable, but it will have to pay for it with higher electricity consumption.

The circuit with a buffer electric boiler has three main disadvantages.

First, it's pretty significant electricity consumption for heating water. Electricity is consumed to compensate for heat losses (water cooling) when storing hot water in the boiler, as well as to heat that part of the water that comes from the boiler to the boiler with cold water.

Part of the water from the boiler enters the boiler cold. This happens during the period when the boiler DHW mode is started at each opening of the water tap, as well as in the case of the boiler cycle. In addition, cold water from the boiler is supplied to the boiler in the event of an insignificant hot water consumption, when the flow is less than the minimum threshold required to start the boiler in DHW mode.

Electricity is also consumed for water heating if the boiler thermostat is set to a temperature higher than 60 o C.

The second disadvantage is that the boiler's DHW mode is still activated every time the water tap is opened. The boiler cycle is not eliminated, but only becomes invisible to the consumer. All this, as already mentioned above, reduces the resource of the boiler, and frequent re-ignition of the burner reduces the efficiency of the boiler and increases the gas consumption. Some owners find it beneficial turn on the DHW mode on the boiler only when taking a shower or filling the bath. For washing dishes and in other cases when the need for hot water is small, the water in the boiler is heated only by electricity.

Thirdly, the dependence of the pressure in the DHW pipes on the water flow rate remains, since water from the water supply continues to pass through the flow limiter in a double-circuit boiler or column. For this reason, when the second water taps is opened, the water temperature in the first mixer can change, although not so much.

Choosing an electric boiler for a DHW system with a double-circuit boiler or a column

To get the advantages of using hot water from a DHW system with a boiler and an electric boiler, it is enough to install a small-capacity boiler, 30 (50) liters. In addition, a small boiler will consume less electricity than a large one.

I recommend choosing an electric boiler with a stainless steel cylindrical tank. The boiler is often installed next to a boiler or water heater. So that the dimensions of the boiler do not go beyond the dimensions of the boiler, it is convenient to use electric water heaters with a vertical small-diameter tank. The brand name of such boilers usually contains the word Slim.

I recommend, Thermex Ultra Slim IU 30 (or 50) V has a stainless steel tank, a metal body, three power levels of the heating element 0.7 / 1.3 / 2.0 kw., maximum outer diameter 285 mm., and a height of 800 (1235) mm., mechanical control. The warranty is 7 years.

Electric storage water heaters with a flat housing should not be chosen. In the case of flat water heaters, two cylindrical tanks of small diameter are installed side by side and connected with pipes. Such complex design creates problems ensuring their durability, with the distribution of the temperature of the water in the tanks, and also increases their price.

At the end of this article, you will find DHW circuit with boiler and hot water recirculation, as well as recommendations for the selection of equipment.

Where and how much to buy an electric boiler in your city

Electric storage water heater Thermex Ultra Slim IU

DHW system with a double-circuit boiler (or column), but with a layer-by-layer heating boiler eliminates all the disadvantages.

The principle of operation of the DHW layer-by-layer boiler

Recently the DHW system with a layer-by-layer heating boiler is gaining popularity, water in which is heated by an instantaneous water heater. Such a boiler does not have a heat exchanger, which reduces its cost.

Hot water is drawn from the top of the tank. In its place, cold water from the water supply immediately flows into the lower part of the tank. The water from the tank is pumped through the flow heater of the gas boiler or column, and is supplied directly to the upper part of the tank. Thereby, hot water comes to the consumer very quickly- there is no need to wait until almost the entire volume of water has warmed up, as it happens in an indirect heating boiler.

Rapid heating of the upper layer of water, allows you to install a smaller boiler in the house, as well as reduce the power of the flow heater, without sacrificing comfort.

Manufacturers produce double-circuit boilers with built-in or external layer-by-layer heating boiler. As a result,the cost and dimensions of the DHW system equipment are slightly less,than with an indirect heating boiler

The water in the boiler is heated in advance, whether it is spent or not. The hot water supply in the tank allows you to use hot water in the house for several hours.

Due to this, the water in the tank can be heated for quite a long time, gradually accumulating thermal energy in the hot water.

Long duration of water heating allows use a heater of relatively low power.

Scheme of operation of a storage tank for layer-by-layer heating with a double-circuit boiler

Schematic diagram of connecting a storage tank of layer-by-layer heating to a double-circuit boiler

In the diagram, the arrows show the direction of water movement in the DHW circuit of the boiler during the operation of the circulation pump. The pump is switched on by a temperature sensor, boiler thermostat.

The circulation of water in the DHW circuit of the boiler starts the boiler in DHW mode. The water heated by the boiler enters the boiler, where it rises. Cold water from the bottom of the boiler is pumped into the boiler. This continues until the water in the boiler heats up until the boiler temperature sensor is triggered. The sensor turns off the pump, the circulation of water in the heating circuit stops and the boiler's DHW mode is turned off.

Hot water is supplied to the taps from the top of the boiler through a separate pipe. This solution makes it possible to stabilize the temperature of the water supplied to the consumer by simple means. When hot water is consumed from the boiler, it is replaced by cold water from the water supply.

The speed of water circulation in the boiler DHW circuit is chosen so that the water in the boiler has time to heat up to the set temperature quickly enough so that consumers do not experience discomfort. For this, it is convenient to install a pump that allows you to switch the operating speed.

Connecting the boiler to a double-circuit gas boiler

The layer-by-layer heating boiler Galmet SG (S) Fusion 100 L (for double-circuit boilers) has a built-in three-speed circulation pump. Boiler height 90 cm., diameter 60 cm.

On sale you can find layer-by-layer boilers specially designed for connection to a double-circuit boiler. For example, the figure shows a diagram of connecting a boiler made in Poland to a boiler.

Thanks to the technology of layer-by-layer heating of water with the accumulation of hot water in the boiler, the number of boiler starts is reduced, which prolongs its service life and reduces gas consumption.

Uniform water temperature (without sudden changes) ensures comfortable use of water at more than one draw-off point.

The boiler has five connections for connecting external pipelines. Moreover, the ends of the pipes inside the boiler are at different heights. Such a large number and arrangement of nozzles allows the boiler to function as a low loss header. This solution eliminates the mutual influence on the circulation mode and water temperature in different circuits of the system and makes it easier and cheaper to connect equipment with fittings.

For example, two nozzles are designed for the hot water recirculation circuit in the distribution pipes around the house. The waiting time for hot water will not depend on the length of the pipes to the place where the water is drawn. The DHW heating circuit of the boiler is connected to the other two branch pipes. There is also a separate pipe for cold water from the mains.

An expansion tank and a safety valve are connected to the cold water supply pipe from the water supply system, and a check valve (not shown in the diagram) is installed.

The floor-standing boiler is also good in that dirt and sludge settles and accumulates at the bottom, does not fall into the pipes and does not affect the operation of the equipment.

How to make a layer-by-layer boiler from an electric boiler

Continued: go to

In order for the BKN to work correctly, a working diagram for connecting an indirect heating boiler is needed. In this case, the heating will also function, and hot water will be in the house in the required quantities at all points of analysis.

The piping of the indirect heating boiler itself does not cause any particular difficulties, the same materials and fittings are used as for any work on hot water, both with and with a hot tap water supply system.

The principle of operation of the BKN and the parameters for its choice, calculations by volume and models, see the next review in the section "Boilers to boilers".

Here we will dwell in more detail on the question of how to connect an indirect heating boiler in steam to a heating boiler, consider possible options and comment on the diagram.

So let's go.

BKN location in the house

The closer the BKN is to the boiler, the more efficiently heat is removed and heat is transferred from CO to DHW. Usually, the installation of an indirect heating boiler is carried out, although I have seen several options for installing a BKN in corridors, bathrooms and other utility rooms.

In this case, of course, the efficiency of heat removal will be inferior to the option when the circuit for connecting an indirect heating boiler is implemented in the boiler room, directly at the boiler.

However, this option also has its own plus - hot water consumers are getting closer to the BKN, which means that the heat loss through the hot water supply is noticeably reduced, and the waiting time for hot water in systems without circulation is reduced.

How to put a BKN in a boiler room

In total, there are 4 types of BKN location in the boiler room in nature. These are wall-mounted horizontal and vertical boilers, and floor-standing BKN installed horizontally and vertically. The first ones have fittings for mounting on the wall, the second ones do not have such fittings, but they have stands for installation on the floor in the boiler room.

Wall-mounted BKNs are usually of small volume - from 30 to 200 liters, floor-mounted ones - from 200 to 1500 liters. An attempt to hang a floor-standing boiler on the wall can end in disaster. Imagine that you have hung an 800-liter outdoor BKN on the wall from an aerated concrete block. These 900 kilograms of water and steel will eventually knock your wall down. And behind one they will pour boiling water over the entire first floor.

Therefore, the installation of an indirect heating boiler should take place exactly as its manufacturer intended. Wall-mounted - hung on the wall, floor-mounted - placed on the floor.

Installing an indirect heating boiler on the wall is no different from attaching the most ordinary electric water heater - the same anchor, the same procedure.

The only moment! When you install an indirect heating boiler, make sure that the inlet and outlet pipes for the supply and outlet of the coolant to the CO "look" to the side.

Otherwise, you will have to suffer a lot, you will heap up the whole system of pipes, corners and contours, the piping of the indirect heating boiler will be a "curve".

And if everything is done correctly, then you will have only 2 direct branches from the CO system. The beauty!

The correct installation diagram for the indirect heating boiler is shown below.

Installation diagram of the indirect heating boiler - WALL-MOUNTED OPTION:

Installation diagram of an indirect heating boiler - FLOOR VERSION:

Connecting an indirect heating boiler to CO and DHW

After the BKN is established in its rightful place in the boiler room or bathroom, the next stage is to connect the indirect heating boiler.

It is quite simple to do this, because how to connect an indirect heating boiler to CO and to hot water supply is within the power of any normal man with the very minimum of tools.

In the BKN itself, there are only four nozzles - the inlet and outlet of the hot coolant of the heating system, and the inlet of cold water and the outlet of hot water of the DHW system. In the case when circulation is organized in the DHW system, the last two pipes will be - the inlet of circulating warm water from the DHW system and the outlet of heated water back to the DHW system with circulation.

Until the taps at the points of analysis are open, the water circulates through the DHW system and is heated by the boiler to the desired temperature. As soon as the tap at the point of parsing is open, the water went "on demand" to the consumer.

To make the connection of an indirect heating boiler, you need to connect the first two nozzles to, and the second two nozzles to the hot water supply system.

When the combined boiler is operating, the water in the BKN will be heated not only from the coolant in the heating system, but can also be heated up to the values ​​set by the consumer using the built-in BKN.

Below is a diagram for connecting an indirect heating boiler when the BKN is located directly in the boiler room.

Indirect heating boiler piping - WALL MOUNTING DIAGRAM:

Boiler piping for indirect heating - DIAGRAM FOR FLOOR INSTALLATION:

In the case of DHW, in which the circulation of hot water is implemented, a circulation pump is added to the circuit, which stands in front of the DHW inlet in front of the BKN.

As a result, the entire DHW and CO circuit with the BKN connection will look like this:

The piping of the indirect heating boiler must be carried out in such a way that the device can be excluded from the general scheme. For this purpose, a bypass is provided for all inputs / outputs - CO and DHW.
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