How to connect a gas boiler with solid fuel in one system. A heating system with two boilers is the best alternative for continuous heating of a building

The two-boiler scheme has been very widely used recently, and there is quite a lot of interest. When two thermal units appear in one boiler room, the question immediately arises of how to coordinate their work with each other. Let's try to answer the question of connecting two boilers to one heating system.

This information will be of interest to those who are going to build their own boiler house, who want to avoid mistakes and for those who are not going to build with their own hands, but want to convey their needs to those people who will assemble the boiler house. It is no secret that each installer has his own ideas about how the boiler room should look and often they do not coincide with the needs of the customer, but the customer's desire is more important in this situation.

Let us analyze examples of why in one case the boiler room operates in automatic mode (the boilers are coordinated with each other without the participation of the consumer), and in the other it is required that it be turned on.

Nothing is required here, except for shut-off valves. Switching between boilers is carried out by manual opening / closing of two taps located on the coolant. And not four, in order to completely cut off the idle boiler from the system. In both boilers, most often there are built-in ones and it is more profitable to use them both at the same time, because the volume of the heating system very often exceeds the capabilities of one expansion tank taken separately. In order to avoid the useless installation of an additional (external) expansion tank, it is not necessary to cut off the boilers from the system completely. It is necessary to shut them off according to the movement of the coolant and leave them simultaneously included in the expansion system.

Connection diagram for two boilers with automatic control

Important! The valves must work towards each other, then the coolant from the two boilers will move only in one direction, towards the heating system.

For an automatic system for the simultaneous operation of two boilers, an additional part is needed - this is a thermostat that will turn off the circulation pump if there is a wood-burning boiler or any other boiler with manual loading in the system. It is necessary to turn off the pump at the boiler. Because when the fuel burns out in it, it makes no sense to drive the coolant through this boiler for nothing, interfering with the operation of the second boiler. Which will pick up the work when the first one stops. With the maximum diameter and the highest brand of thermostat to turn off the pump, you will spend no more than 4000 rubles and get an automatic system.

Video of the implementation of two boilers in one boiler room

The feasibility of using automatic and manual switching between two boilers

Consider the following five options with different units in conjunction with an electric boiler, which is in reserve and must turn on at the right time:

Gas + Electric
Firewood + Electric
LPG + Electro
Solar + Electro
Pellet (granular) + Electro

Pellet and electric boiler

Combination of connecting two boilers - pellet and electric boilers– best suited for automatic activation and manual activation is also acceptable.

The pellet boiler may stop due to the fact that it has run out of fuel pellets. It got dirty and wasn't cleaned. The electric must be ready to turn on instead of the stopped boiler. This is only possible with automatic connection. Manual connection in this option is only suitable if you permanently live in a house where such a heating system is installed.

Boilers for diesel fuel and electricity

If you live in a house with such a system for connecting two heating boilers, a manual connection is quite suitable for you. The electric boiler will work as an emergency in case the boilers fail for some reason. Not just stopped, but broken and in need of repair. It is also possible to switch on automatically as a function of the time. The electric boiler can work in pairs with liquefied gas and a solar boiler at a nightly rate. Due to the fact that the night rate is cheaper for 1 kW / hour than 1 liter of diesel fuel.

Combination of electric boiler and wood burning

This combination of connecting two boilers is more suitable for automatic connection and less for manual connection. The wood burning boiler is used as the main one. It heats the room during the day, and the electric turns on to heat it up at night. Or in the case of a long stay in the house - an electric boiler maintains the temperature so as not to freeze the house. Manual is also possible to save electricity. The electric boiler will turn on manually when you leave and turn off when you return and start heating the house with a wood-fired boiler.

Combination of gas and electric boilers

In this combination of connecting two boilers, the electric boiler can act both as a backup and as a main one. In this situation, a manual connection scheme is more suitable than an automatic one. The gas boiler is a proven and reliable unit that can work for a long time without breakdowns. In parallel, it is not advisable to connect an electric boiler to the system for safety net in automatic mode. In the event of a gas boiler failure, you can always turn on the second unit manually.

In order to save money, it is often used to connect two boilers to one heating system. When purchasing several thermal devices, you should know in advance what methods exist for connecting them together.

Since the wood-burning boiler operates in an open system, it is not easy to combine it with a gas heater that has a closed system. With an open-type piping, the water is heated to a temperature of one hundred degrees or more at the highest high pressure. To protect the overheating of the liquid, an expansion tank is placed.

Part of the hot water is discharged through open-type tanks, which helps to reduce the pressure in the system. But the use of such trigger tanks sometimes causes oxygen particles to enter the coolant.

There are two ways to connect two boilers into one system:

parallel connection of a gas and solid fuel boiler together with safety devices;
serial connection of two boilers of different types using a heat accumulator.

With a parallel heating system in large buildings, each boiler heats its own half of the house. The serial combination of a gas and wood-burning unit form two separate circuits, which are combined with a heat accumulator.

The use of a heat accumulator

The heating system with two boilers has the following structure:

a heat accumulator and a gas boiler are combined with heating appliances in a closed circuit;
energy flows from the wood-burning heater to the heat accumulator, which are transferred to a closed system.

With the help of a heat accumulator, it is possible to carry out the operation of the system simultaneously from two boilers or only from a gas and wood-burning thermal unit.

Parallel closed circuit

To combine the systems of a wood and gas boiler, the following devices are used:

safety valve;
membrane tank;
manometer;
air vent valve.

First of all, shut-off valves are mounted on the pipes of two boilers. A safety valve, a device for venting air, and a pressure gauge are installed near the wood-burning unit.

A switch is placed on the branch from the solid fuel boiler for the functioning of the turnover of the small circle. Fix it at a distance of one meter from a wood-burning heater. A non-return valve is added to the jumper, blocking the access of water to part of the circuit of the evacuated solid fuel unit.

The return flow is connected to the radiators. The return flow of the coolant is separated by two pipes. One is connected through a three-way valve to the jumper. Before branching these pipes, a tank and a pump are mounted.

A heat accumulator can be used in a parallel heating system. The installation scheme of the device with such a connection consists in connecting to it the return and supply lines, supply and return pipes to the heating system. For the joint or separate operation of the boilers, valves are installed at all system nodes that block the flow of the coolant.

It is possible to combine two heaters using manual and automatic control.

Connection with manual control

Turning on and off the boilers is carried out manually due to two taps on the coolant. The binding is carried out using shut-off valves.

Expansion tanks are installed in both boilers, which are used simultaneously. Experts recommend not to completely cut off the boilers from the system, but simply connect them to the expansion tank at the same time, blocking the movement of water.

Connection with automatic control

A non-return valve is installed for automatic adjustment of two boilers. It protects the shutdowns of the heating unit from harmful flows. Otherwise, the method of coolant circulation in the system is no different from manual control.

In an automatic system, all main lines must not be blocked. The pump of the working boiler drives the coolant through the non-working unit. Water moves in a small circle from the place where the boilers are connected to the heating system through an idle boiler.

In order not to consume most of the coolant for an unused boiler, check valves are installed. Their work should be directed at each other so that the water from the two thermal equipment is directed to the heating system. Valves can be put on the return flow. Also, with automatic control, a thermostat is needed to regulate the pump.

Automatic and manual control is used when combining different types of heaters:

gas and solid fuel;
electric and wood;
gas and electric.

It is also possible to connect two gas or electric boilers to one heating system. Installing more than two connected thermal units leads to a decrease in the efficiency of the system. Therefore, more than three boilers are not connected.

Benefits of a Dual Boiler System

The main positive aspect of installing two boilers in one heating system is the continuous support of heat in the room. A gas boiler is convenient in that it does not need to be constantly serviced. But in case of emergency shutdown or in order to save money, a wood-burning boiler will become an indispensable heating supplement.

The heating system of two boilers allows you to significantly increase the level of comfort. The advantages of a dual thermal device include:

choice of the main type of fuel;
the ability to control the entire heating system;
increasing the operating time of the equipment.

Connecting two boilers to one heating system is the best solution for heating buildings of any size. Such a solution will allow you to continuously keep warm in the house for many years.

Consider heating systems consisting of a gas boiler and an electric boiler. Why install such systems? There are several options, either for duplicating the heating system, if it fails from the devices for some reason, then the consumer will be able to use another. But in most cases, the installation of an electric boiler is used to use it at night, when the electricity tariff is minimal, subject to a formalized tariff for electric heating and the presence of a 2-tariff electricity meter. The economic benefit of using an electric boiler at night is 2.52 times. If electric heating is used as an auxiliary system.

We compare the performance and cost of electric heating with gas.

If the efficiency of electric boilers is about 98%, then the majority of gas boilers have an efficiency of about 90%, with the exception of condensing boilers, which have an efficiency of more than 100%. However, it should be taken into account that when calculating the efficiency of most gas boilers ((especially those imported from Germany, Italy and others), the calorific value of gas was taken into account on the order of 8250 kcal per 1 cubic meter of gas. However, in the current situation, gas is supplied through a mixed system. The minimum calorie content of mixed gas should not be lower than 7600 kcal.As practice shows, many gas consumers during the heating period declare that the gas supplied to them is much lower than 7600 kcal.Therefore, with low-calorie gas, the efficiency of branded gas boilers will be declared by the manufacturer.

In the calculations, we will use the calorific value of gas as 7600 kcal, since this is the minimum allowable calorie content according to existing legislation. If we compare the calorific value of gas and electricity with an efficiency equal to 100%, we get

7600 kcal = 8.838 kW = 1 cubic meter of gas.

In practice, 100% can be obtained only on condensing boilers, all the rest will work on the fact of 82% or less. That is, when using low-calorie gas to generate 7600 kcal of heat, it will be necessary to spend not 1 cubic meter of gas, but 1.18 cubic meters of gas.

If electric heating is used as an auxiliary system.

7600 kcal	Fuel	efficiency %	Consumption	Price	Outcome	Benefit
	Gas	82	1.18 cu	6,879	8,11	2.52 times
	Electro	98	9.014 kW	0,357*	3,217	2.52 times

* In the calculation, a tariff of 0.357 UAH per 1 kW was used, provided that the tariff for electric heating was issued, and the main load on the boiler falls from 23.00 to 7.00, those electric heating acts as an additional system.

What you need to pay attention to when installing an electric boiler, when installing it into an existing heating system, where the main source of heating was a gas boiler.

Fig. 1 Scheme of serial connection of an electric boiler T with a gas boiler without a built-in safety group and an expansion tank. KE1 - electric boiler, KG1 - gas boiler without a built-in safety group and expansion tank, BR1 - expansion tank, RO - heating radiators, V - shutoff valves, VR - control valves, KZ1 - relief valve, PV - automatic air blower, M1 - pressure gauge, F1 filter.

In most cases, each heating system is individual. Very often, the consumer has a gas boiler installed as a single module, i.e. circulation pump and expansion tank already installed in the boiler. Many installers very often offer to save your money and offer to install an electric boiler in series, i.e. both boilers operate in a common flow. The meaning of saving lies in the fact that you will be offered to purchase a cheap boiler in which there is neither an expansion tank nor a circulation pump. Such an electric boiler will indeed be cheaper than a fully equipped one. Many do not really hesitate to agree to such an offer. However, this is a dubious method of saving, since most of the functions in such a scheme are carried out by a gas boiler, and in case of emergency shutdown of a gas boiler, for example, failure of the circulation pump, or expansion tank, etc., etc. The whole system will stop.

On the one hand, you have two sources for heating, and on the other hand, you are highly dependent on the performance of the gas boiler. Conclusion - serial connection of an electric boiler will not always provide you with complete comfort.

The second method of installing an electric boiler in a heating system with a gas boiler is a parallel installation.

This method of installation is considered the most correct, since you get two heating sources independent of each other, and in the event of a failure of one, you can fully use the other. With a slightly larger initial investment, you will receive the most reliable and comfortable heating system.

Installing a solid fuel boiler is the first step to efficient and economical maintenance of heat in the house. The next steps are to regularly add firewood or other solid fuels. It is necessary to maintain the temperature of the heat carrier of the heating system within operating limits even at night. And even when the house is visited only on weekends, it is required to maintain a minimum temperature in order to avoid moisture condensation on the internal surfaces in the room.

If the presence of condensate is not critical, then when leaving after the weekend, you need to wait for the boiler to stop and drain the water from the heating system in order to prevent the system from freezing. In case of draining water, all metal elements corrode when exposed to air.

Draining the coolant is not necessary if antifreeze is used instead of water. However, when using antifreeze, due to high fluidity, high demands are placed on threaded seals and on valves.

The most common solution for maintaining the temperature in the heating circuit is to install an electric boiler together with a solid fuel one. The minimum amount of additional equipment will allow the electric boiler to automatically take over the heating functions, and the solid fuel boiler to turn off, without the risk of boiling. Also, the use of an electric boiler eliminates the need to carry out any manipulations with the heating system, leaving a country house until the next weekend. To track emergency situations and remotely control an electric boiler, there is one that controls the operating mode of heating equipment.

Types of electric boilers

When choosing an electric boiler for installation in addition to a solid fuel one, it is enough to briefly familiarize yourself with the basics of heating water using electric current so as not to fall into the network of marketers. Electric boilers operate with an efficiency of about 95%. It is not worth checking on your heating system the veracity of the manufacturer's assurances about the incomparably high efficiency of their devices - this can cost extra money, and they will not pay off soon. There are three main types of boilers:

Heating in them is carried out by an electric heating element (heater), which is immersed directly in the coolant. In the circuit of such a boiler, both water and antifreeze can circulate. It is unpretentious in operation, but periodically requires the replacement of the heating element due to the formation of scale, which reduces heat transfer.

The heat carrier in them is water. Heating occurs due to the energy released during the flow of electric current through the coolant in the boiler between the electrodes that are inside. It can work without an electric pump in the circuit. Provides smooth heating of water in the system. Over time, as a result of electrolytic reactions, the electrodes dissolve and need to be replaced.

Any kind of coolant is heated by vibrations caused by an induction coil. The temperature from the heating element is evenly distributed over the surface of the flow tank, which almost completely eliminates the possibility of scale formation. For the efficient use of the boiler, high-quality control automation is required.

Due to the high price, induction boilers are inferior to heating elements and electrode ones. Given the auxiliary function of the electric boiler, the issue of return on investment in advanced technology fades into the background. The main selection criteria remain: power, quality of the materials of the device, build quality and equipment.

Solid fuel boiler connection diagram

The most efficient connection scheme for solid fuel (TTK) and electric (EC) boilers is parallel. The supply to the heating system of both boilers is carried out at one point, as well as the return. This scheme eliminates the inconsistency of pump operation and heat loss in the TTK heat exchanger when the EC is running. The algorithm of such a system can be described as follows:

working TTK maintains a comfortable temperature in the room;
the fuel burned out, the coolant cools down, and when the specified minimum temperature is reached, the thermostat turns off the pump;
the air temperature in the room drops below the comfortable one (set by the user) and the EC turns on.

For the correct operation of the system, it is necessary to take into account some features of connecting devices and fittings. The performance of the T.T.K. pump must be greater than that of the EK pump so that the simultaneous operation of the boilers does not affect the speed of the coolant through the TTK heat exchanger. In the heating system, a non-return valve must be installed at the supply of each boiler to prevent backflow.

To control the operation of the TTK pump, a thermostat is used that measures the temperature of the coolant at the supply to the check valve. A remote air temperature sensor that controls the activation of the EC must be placed in one of the heated rooms.

To control the EC, they are also used, which allow, using mobile communications, to set the temperature mode for turning on or off the boiler. This method will allow you to program the boiler to turn on only at night to save energy and maximize the benefits of multi-zone billing. You can also set the required air temperature, for example, a few hours before arriving at the cottage.

With the right choice of equipment and fittings for the boiler room, the power of two boilers connected according to the proposed scheme will ensure uninterrupted heat supply, creating coziness and comfort in the house. And for owners of country houses - an additional convenience of controlling the heating system.

The efficiency of its further operation and service life depend on how correctly the binding of a solid fuel boiler is made. In operation, wood and coal heat generators differ from units using other types of fuel, therefore they require a special approach.

It is proposed to consider in detail how, after installing the heating wiring, connect a solid fuel boiler, including with your own hands. You can find a description of the various schemes for connecting a TT boiler to a heating system in this material.

What is the difference between solid fuel boilers

In addition to burning various types of solid fuels, heat generators have a number of differences from other heat sources. These features should be taken for granted and always taken into account when tying a solid fuel boiler with a water heating system. What are they:

High inertia. At the moment, there are no ways to abruptly extinguish a burning solid fuel in a combustion chamber.
Formation of condensate in the firebox during warm-up. The peculiarity is manifested due to the entry of a coolant with a low temperature (below 50 ° C) into the boiler tank.

Note. The phenomenon of inertia is absent only in one type of solid fuel units - pellet boilers. They have a burner, where wood pellets are dosed, after the supply is stopped, the flame goes out almost immediately.

Scheme of the device of a TT-boiler of direct combustion with forced air injection

Inertia creates a danger of overheating of the water jacket of the heater, as a result of which the coolant boils in it. Steam is formed, which creates high pressure, tearing the body of the unit and part of the supply pipeline. As a result, there is a lot of water in the furnace room, a lot of steam and a solid fuel boiler unsuitable for further operation.

A similar situation may arise when the heat generator is connected incorrectly. After all, in fact, the normal mode of operation of wood-burning boilers is the maximum, it is at this time that the unit reaches its passport efficiency. When the thermostat responds to the heat carrier reaching a temperature of 85 ° C and closes the air damper, combustion and smoldering in the furnace still continues. The temperature of the water rises by another 2-4°C, or even more, before its growth stops.

In order to avoid excess pressure and a subsequent accident, an important element is always involved in the piping of a solid fuel boiler - a safety group, more about it will be discussed below.

Another unpleasant feature of the operation of the unit on wood is the appearance of condensate on the inner walls of the firebox due to the passage of an unheated coolant through the water jacket. This condensate is not God's dew at all, since it is an aggressive liquid, from which the steel walls of the combustion chamber quickly corrode. Then, having mixed with the ash, the condensate turns into a sticky substance, it is not so easy to tear it off the surface. The problem is solved by installing a mixing unit in the piping circuit of a solid fuel boiler.

Such a deposit serves as a heat insulator and reduces the efficiency of a solid fuel boiler.

It is too early for owners of heat generators with cast-iron heat exchangers that are not afraid of corrosion to breathe a sigh of relief. They can expect another misfortune - the possibility of destruction of cast iron from temperature shock. Imagine that in a private house the electricity was turned off for 20-30 minutes and the circulation pump, which drives water through a solid fuel boiler, stopped. During this time, the water in the radiators has time to cool down, and in the heat exchanger - to heat up (due to the same inertia).

Electricity appears, the pump turns on and sends the cooled coolant from the closed heating system to the heated boiler. From a sharp temperature drop, a temperature shock occurs at the heat exchanger, the cast-iron section cracks, water runs to the floor. It is very difficult to repair, it is not always possible to replace the section. So even in this scenario, the mixing unit will prevent an accident, which will be discussed later.

Emergencies and their consequences are not described in order to scare users of solid fuel boilers or encourage them to purchase unnecessary elements of piping circuits. The description is based on practical experience, which must always be taken into account. With the correct connection of the thermal unit, the likelihood of such consequences is extremely low, almost the same as for heat generators using other types of fuel.

How to connect a solid fuel boiler

The canonical scheme for connecting a solid fuel boiler contains two main elements that allow it to function reliably in the heating system of a private house. This is a safety group and a mixing unit based on a temperature sensor, shown in the figure:

The always open outlet of the mixing valve (left connection in the diagram) must be directed to the pump and the heat generator, otherwise there will be no circulation in the small boiler circuit

Note. The expansion tank is not conventionally shown here - it must be connected to the return line of the heating system in front of the pump (in the direction of the water flow).

The presented diagram shows how to connect the unit correctly and is used with any solid fuel boilers, including pellet ones. You can find various general heating schemes - with a heat accumulator, an indirect heating boiler or a hydraulic arrow, on which this unit is not shown, but it must be there. The method of protection against moisture loss in the furnace is discussed in detail in the video:

The task of the safety group, installed directly at the outlet of the solid fuel boiler inlet pipe, is to automatically relieve the pressure in the network when it rises above the set value (usually 3 bar). It does this, and besides it, the element is also equipped with a pressure gauge. The first releases the air that appears in the coolant, the second serves to control pressure.

Attention! On the section of the pipeline between the safety group and the boiler, it is not allowed to install any shutoff valves. If you have installed a ball valve for cutting off and repairing group parts, remove the handle from the stem.

How the scheme works

The mixing unit, which protects the heat generator from condensate and temperature extremes, operates according to the following algorithm, starting from kindling:

Firewood is just flaring up, the pump is on, the valve on the side of the heating system is closed. The coolant circulates in a small circle through the bypass.
When the temperature in the return pipeline rises to 50-55 °C, where the remote-type overhead sensor is located, the thermal head, at its command, begins to press the three-way valve stem.
The valve slowly opens and cold water gradually enters the boiler, mixing with hot water from the bypass.
As all radiators warm up, the overall temperature rises and then the valve closes the bypass completely, passing all the coolant through the unit heat exchanger.

An important nuance. Paired with a 3-way valve, a special head with a sensor and a capillary is installed, designed to regulate the water temperature in a certain range (for example, 40 ... 70 or 50 ... 80 degrees). A conventional radiator thermal head will not work.

This piping scheme is the simplest and most reliable, you can safely install it yourself and thus ensure the safe operation of the solid fuel boiler. Regarding this, there are a couple of recommendations, especially when tying a wood-burning heater in a private house with polypropylene or other polymer pipes:

Make a section of the pipe from the boiler to metal, and then lay plastic.
Thick-walled polypropylene does not conduct heat well, which is why the overhead sensor will frankly lie, and the three-way valve will be late. For the unit to work correctly, the area between the pump and the heat generator, where the copper bulb stands, must also be metal.

Connection with copper pipes will not protect polypropylene from destruction in case of overheating of the TT boiler. But it will allow the temperature sensor and the safety valve on the safety group to work correctly

Another point is the installation location of the circulation pump. It is best for him to stand where he is shown in the diagram - on the return line in front of the wood-burning boiler. In general, you can put the pump on the supply, but remember what was said above: in an emergency, steam may appear in the supply pipe.

The pump is unable to pump gases, therefore, when the chamber is filled with steam, the impeller will stop, the circulation of the coolant will stop. This will accelerate the possible explosion of the boiler, because it will not be cooled by the water flowing from the return.

Way to reduce the cost of strapping

The condensate protection scheme can be reduced in cost by installing a three-way mixing valve of a simplified design that does not require the connection of an attached temperature sensor and a thermal head. A thermostatic element is already installed in it, set to a fixed mixture temperature of 55 or 60 ° C, as shown in the figure:

Special 3-way valve for solid fuel heating units HERZ-Teplomix

Note. Similar valves that maintain a fixed temperature of the mixed water at the outlet and are designed for installation in the primary circuit of a solid fuel boiler are produced by many well-known brands - Herz Armaturen, Danfoss, Regulus and others.

The installation of such an element definitely allows you to save on piping a TT boiler. But at the same time, the possibility of changing the temperature of the coolant with the help of a thermal head is lost, and its deviation at the outlet can reach 1-2 °C. In most cases, these shortcomings are not significant.

Binding option with buffer tank

The presence of a buffer tank is highly desirable for the operation of the boiler on solid fuels, and here's why. In order for the unit to function efficiently and produce heat with the efficiency stated in the passport (from 75 to 85% for different types), it must operate at maximum mode. When the air damper is closed in order to slow down combustion, there is a lack of oxygen in the furnace and the efficiency of burning wood decreases. At the same time, emissions of carbon monoxide (CO) into the atmosphere increase.

For reference. It is precisely because of emissions that in most European countries it is forbidden to operate solid fuel boilers without a buffer tank.

On the other hand, with maximum combustion, the temperature of the coolant in modern heat generators reaches 85 ° C, and one laying of firewood lasts only 4 hours. This does not suit many owners of private houses. The solution to the problem is to put a buffer tank and include it in the piping of the TT boiler so that it serves as a storage tank. Schematically it looks like this:

By measuring the temperature T1 and T2, you can adjust the layer-by-layer loading of the tank with a balancing valve

When the firebox burns with might and main, the buffer tank accumulates heat (in technical terms, it is loaded), and after attenuation it releases it to the heating system. To control the temperature of the coolant supplied to the radiators, on the other side of the storage tank, a three-way mixing valve and a second pump are also installed. Now it is not at all necessary to run to the boiler every 4 hours, because after the attenuation of the firebox, the buffer capacity will provide heating for the house for some time. How long - depends on its volume and heating temperature.

Reference. Based on practical experience, the capacity of a heat accumulator can be determined as follows: a private house with an area of 200 m² will need a tank with a volume of at least 1 m³.

There are a couple of important nuances. In order for the piping scheme to work safely, a solid fuel boiler is needed, whose power is enough for simultaneous heating and loading of the buffer tank. This means that the power required is 2 times higher than the calculated one. Another point is the selection of pump performance in such a way that the flow rate in the boiler circuit slightly exceeds the amount of water flowing in the heating circuit.

An interesting option for docking a TT-boiler with a home-made buffer tank (it is also an indirect heating boiler) without a pump was demonstrated by ours in the video:

Joint connection of two boilers

To increase the comfort of heating a private house, many owners install two or more heat sources that operate on different energy carriers. At the moment, the most relevant combinations of boilers are for:

natural gas and firewood;
solid fuel and electricity.

Accordingly, a gas and solid fuel boiler must be connected in such a way that the second one automatically replaces the first one after burning the next portion of firewood. The same requirements are put forward for piping an electric boiler with wood burning. This is quite simple to do when a buffer tank is involved in the piping scheme, since it simultaneously plays the role of a hydraulic gun, which is shown in the figure.

The supply lines of the boilers are connected to the upper branch pipes of the heat accumulator, the return lines - to the lower ones.

Advice. You will find information on calculating the volume of the buffer tank.

As you can see, due to the presence of an intermediate storage tank, 2 different boilers can serve several heating distribution circuits at once - batteries and underfloor heating, and in addition load an indirect heating boiler. But not everyone puts a heat accumulator with a TT boiler, since this is not a cheap pleasure. In this case, there is a simple scheme, and you can mount it yourself:

The scheme takes into account the peculiarity of the electric boiler - the built-in circulation pump always works

Note. The scheme is valid for both electric and gas heat generators operating together with solid fuel.

Here the main source of heat is a wood-burning heater. After the firewood load burns out, the air temperature in the house begins to fall, which registers the room thermostat sensor and immediately turns on the heating with an electric boiler. Without a new load of firewood, the temperature in the supply pipe decreases and the overhead mechanical thermostat turns off the pump of the solid fuel unit. If after some time it is ignited, then everything will happen in the reverse order. Details about this method of joint connection are described in the video:

Tying with the method of primary and secondary rings

There is another way to jointly tie a solid fuel boiler with an electric one to provide a large number of consumers. This is a method of primary and secondary circulation rings, which provides for hydraulic separation of flows, but without the use of a hydraulic arrow. Also, for reliable operation of the system, a minimum of electronics is required, and the controller is not needed at all, despite the apparent complexity of the circuit:

The trick is that all consumers and boilers are connected to one primary circulation ring by both the supply and return pipelines. Due to the small distance between the connections (up to 300 mm), the pressure drop is minimal compared to the head of the main circuit pump. Due to this, the movement of water in the primary ring does not depend on the operation of the secondary ring pumps. Only the temperature of the coolant changes.

Theoretically, any number of heat sources and secondary rings can be included in the main circuit. The main thing is to choose the right pipe diameters and the performance of pumping units. The actual performance of the main ring pump must exceed the flow in the most "gluttonous" secondary circuit.

To achieve this, it is necessary to perform a hydraulic calculation and only then will it be possible to choose the right pumps, so an ordinary homeowner cannot do without the help of specialists. In addition, it is necessary to link the operation of solid fuel and electric boilers by installing shut-off thermostats, as described in the following video:

Conclusion

As you can see, it is not so easy to properly piping a solid fuel boiler. The issue must be taken responsibly and before performing installation and connection work, additionally consult with a specialist whose qualifications are beyond doubt. For example, with someone who gives explanations in the videos presented.