Stove heating with a water circuit: device

In many private houses, heating with wood and stoves remains a priority. Someone has a metal stove, someone has a brick one, but one thing unites them – this type of heating is not the most convenient. Too much attention and not enough comfort. Exit – stove heating with a water circuit.

First, let’s understand the terminology. When they say “stove”, most often they mean a heater made of bricks, which is heated with wood. But often a metal stove on wood or on coal is also called that. The principles of operation for brick and metal units are the same, the method of heat transfer is changing. Metallic ones have a greater convective component (most of the heat is transferred by air), brick ones are dominated by thermal radiation – from the walls of the furnace and the heated walls of the house. In our article, we are mainly talking about brick ovens, but most of the information can be applied to metal wood (coal) units. Furnace heating with a water circuit can be made on the basis of furnaces of any kind.

Conventional stove heating: advantages and disadvantages

In our country, houses were traditionally heated with brick stoves, but gradually this type of heating was replaced by water systems. All this is because, along with the advantages, simple stove heating has a lot of disadvantages. First about the benefits:

• The stove transfers most of the heat by thermal radiation, and, as scientists have found, it is better perceived by our body.
• Russian or some other heating stove has a colorful appearance, it is often possible to observe an open flame.
• You can make a brick oven with chimneys for a more complete use of the generated heat.
• Heating of this type is non-volatile – does not depend on the availability of electricity.
• There are models of stoves for heating the second floor (due to the heating shield with smoke channels).
  

Today, stove heating is perceived more as exotic, as it is very rare. It is impossible to argue that it is very pleasant to be near a warm stove. A special atmosphere is created. But there are also many serious drawbacks:

• Uneven heating – it is hot near the stove, cold in the corners.
• Large area occupied by the oven.
• Only those rooms into which the walls of the furnace go out are heated.
• The inability to regulate the heating temperature in individual rooms.
• Low efficiency. For conventional stoves, 60% is already a very good indicator, while modern heating boilers can produce 90% or more (gas).
• The need for frequent maintenance. Melt, adjust the dampers, clean the coals – all this regularly and constantly. Not everyone enjoys it.
  

As you can see, the disadvantages are significant, but some of them can be leveled if a heat exchanger is built into the furnace, which is connected to the water heating system. Such a system is also called furnace water heating or furnace heating with a water circuit.

Water stove heating

When organizing water heating from the furnace, a heat exchanger (water circuit) is built into the furnace, which is connected by pipes to radiators. A coolant circulates in the system, which carries the heat from the furnace to the radiators. This solution increases the comfort of living in winter. The thing is that radiators can be installed in any room, that is, the stove can stand in one room, and all other rooms will be heated by batteries through which heated water runs.

At the same time, the remaining disadvantages of stove heating remain, but the advantages of water heating are added – you can adjust the temperature in each room (within certain limits), a large inertia smoothes out the uneven temperature regime. By the way, the same scheme works with metal stoves on wood or coal.

Types of systems

There are two types of water heating systems: forced circulation and natural circulation (EC). Heating with natural circulation is non-volatile (electricity is not required for operation), the coolant circulates due to natural physical processes. The disadvantage of this method of heating is the need to use pipes of large diameter, that is, the volume of the system will be large and will have a large inertia. When kindling the stove, this is not very good – it will take a long time to warm up. But after burning out, heat is retained in the house longer.

Another disadvantage is that to create conditions for the movement of the coolant, the supply pipe is lifted up – to the ceiling or to the level of radiators (in extreme cases). When heating a two-story house, the pipe goes up from the boiler, goes through the radiators, and then goes down and bypasses the batteries on the lower floor.

Another important drawback is the relatively low efficiency of heating systems with EC – the coolant moves slowly, carries little heat.

Furnace heating with a water circuit and forced circulation is distinguished by the presence of a circulation pump (pictured below), which runs constantly. Its task is to drive water at a certain speed. By changing this speed, you can change the intensity of space heating. This leads to the fact that, ceteris paribus, such heating is more efficient. But for the system to work, power is needed – the pump must work constantly. When it stops, the system boils and fails. If you rarely experience power outages, it is enough to have an uninterruptible power supply with a set of batteries. If the light is turned off often and for a long time, you will also have to install a generator, and the total cost of such a solution is considerable.

There is a third type of system: mixed or combined. Everything is designed for natural circulation, but a circulation pump is installed. As long as there is electricity, the heating works as forced (with a pump), when the light is turned off, the coolant moves on its own.

Heat accumulator

Since the stove is not heated all the time, but has a cyclical algorithm of operation, the house is either hot or cold. And the presence of radiators saves little from this. Although the differences are not so critical, they still exist. Especially there is not enough heat at night, but I really don’t want to get up and drown. To solve this problem, a powerful oven is installed, and a heat accumulator is built into the system. This is a large container filled with coolant, which stands between the furnace and the heating system.

That is, there are two separate independent circuits. The first one transfers heat away from the furnace and is usually made with natural circulation. The second drives the coolant into the radiators, and a circulation pump is usually present.

This method of organizing water stove heating is good because while the stove is heating, the water in the tank is actively heated. With the correct calculation, it heats up to 60-80 ° C, which is enough to maintain the normal temperature of the radiators for about 10-12 hours. There is no extreme heat or extreme cold. The atmosphere is quite comfortable.

Installing a heat accumulator in the system (sometimes also called a buffer or buffer tank) also reduces the risk of the system boiling. The second circuit will definitely never boil, but in order for the first one not to boil, it is necessary to correctly calculate it – so that even in the natural circulation mode, the coolant moves at a sufficient speed and does not have time to overheat.

Register for oven

To heat the coolant, a water circuit is built into the furnace (also called a register, heat exchanger, coil, water jacket). Its shape can be any, but most often they make rectangular flat containers or a set of pipes connected into a single system (such as radiators).

To connect the heat exchanger to the system, two pipes are welded into it: one from above – for taking hot water, the second from below – for pumping cooled water from the return pipeline.

Often questions arise with the sizing of the water circuit for the furnace. It can be approximately calculated based on the heat loss of the building. It is believed that to transfer 10 kW of heat, a heat exchanger area of ​​1 sq. m. But at the same time, it is necessary to take into account the operating time of the furnace – after all, it is not heated all the time. While it is not very cold – once a day for about 1,5 hours, when it is cold – twice. During this time, it is necessary that the stove has time to heat all the water in the heat accumulator. Therefore, the calculation of the heat exchanger area is carried out according to the daily amount of heat required to compensate for heat losses.

For example, let the heat loss for a house be 12 kWh. It will be 288 kW per day. The stove is heated, let it take 3 hours, all the necessary heat should accumulate during this time. Then the required power of the water circuit for the furnace is 288 / 3 = 96 kW. To translate it into an area, we divide by 10, we get that for these conditions the register area should be 9,6 m2. Which form you choose is up to you. It is important that the outer surface of the register is not smaller.

Well, a couple more points. The first is that the power of the furnace must be greater than the power of the heat exchanger found. Otherwise, the required amount of heat simply will not be released. The second caveat: the capacity of the heat accumulator must also correspond – it should be more by about 10-15%. In this case, boiling of the coolant is excluded.

Just do not forget that the heat capacity of water and antifreeze is very different. The battery with antifreeze as a coolant must be significantly larger than the water tank (in the same system).

What else is worth remembering is that it is desirable to insulate the heat accumulator well – so that heat is retained longer. In this case, stove heating with a water circuit will be even more economical.

Is it possible to install a register for heating in an existing stove

It is more correct, of course, to build a furnace around the manufactured register. But, if the furnace is already standing, it is still possible to build a water circuit into it. True, you will have to try hard – they are of considerable size and still have to somehow hold on. So the task is not an easy one. In addition, do not forget that you will still have to make two conclusions – to connect the supply and return pipelines.

Finding a location for the register is also not very easy. Its direct contact with fire is highly undesirable, but it must be in an environment of hot gases. In this case, you can hope that the heat exchanger will last a long time.