In the last century, private one-story dwellings were often heated by a wood-burning stove, combined with registers (batteries) of a gravity-fed system. An iron tank was placed inside the heater - a boiler with water heated by the fire of the furnace. This scheme remains attractive due to its non-volatility and low demand for solid fuel quality. Our task is to help the owner choose a stove for a house with water heating, talk about the difficulties of connection and operation.
Water circuit furnaces - 3 varieties
To implement stove heating, combined with the radiator system of a private house, 3 types of stoves with a water circuit are used:
- metal - steel and cast iron stoves with a built-in coil for heating the coolant;
- fireplace inserts with heat exchanger - water jacket;
- brick heating and cooking stoves with built-in boiler.
Note. Potbelly stoves for baths equipped with a tank and a coil are structurally similar to the listed units. It is theoretically possible to adapt a sauna stove for the needs of steam heating, but it is too troublesome and inconvenient from the point of view of operation.
An alternative option should also be included here - do-it-yourself steel wood-fired heaters. Such products deserve attention, since they are not inferior to the factory ones in terms of reliability and heat transfer, but they are much cheaper. The appearance of a potbelly stove does not always play an important role.
We suggest that you consider the stoves of each group separately, focusing on the shortcomings and advantages that are important for the homeowner.
The disadvantages of metal potbelly stoves
In factory-made wood-burning stoves, the coolant is heated in three ways:
- A water tube heat exchanger is installed in the upper area of the firebox or near the flue gas outlet.
- One of the walls of the combustion chamber (top or side) is in contact with a water layer resembling a jacket of a solid fuel boiler.
- Several pipes with a coolant bend around the semicircular walls of the firebox. The bottom and top ends are welded into common collectors, as shown in the drawing.
Reference. An example of a product with a partial water jacket is a Thermofor Hydraulik home heating furnace, with converted pipes Breneran - Aquaten convection heaters with side pipes.
Manufacturers often supply the stoves with an additional heater - heating elements with a power of 1 ... 15 kW. The goal is to maintain the temperature of the coolant and air in a private house after burning out a portion of solid fuel. Some models are equipped with a 1-2 burner hob.
The real advantage of metal heating units is the low cost of the product and the speed of installation compared to the laying of a brick furnace. Example: the price of a 3.5 kW Breneran-Aquatic heater is approximately 270 oz. e. (without chimney). When installing a potbelly stove with your own hands, you will spend another 50-100 c. on materials used for installation and strapping.
Comment. The cost of the chimney required for any stove is not taken into account. The price depends on the height of the lift, the design of the channel and the layout.
Now we will deal with the shortcomings:
- no matter what manufacturers and sellers claim, the maximum efficiency of air-water stoves for wood and coal is 60%;
- the unit heats up and cools equally quickly;
- a heat exchanger is usually enough to heat 2-3 small rooms (1 radiator in each);
- water circuit vital circulation system.
We clarify the last point. If the flow of water through the coil stops, the element overheats.First, the coolant will boil, then evaporate and break the nearest weak connection. Later, the heat exchanger burns out and finally fails.
In fairness, we mention the question of aesthetics. Constantly using a potbelly stove to heat your home, you will not get a beautiful picture that manufacturers like to show in the photo. The stove gets dirty quite quickly, wood and coal dust, the smell of smoke will appear in the room.
Fireplace inserts - pros and cons
A rectangular stove with a water circuit, made in the form of a fireplace, is structurally much closer to the TT boiler. The side walls of the fuel chamber are washed by the coolant, the front and upper part heats the room air. The bottom receives little heat, so it is not taken into account.
Positive sides of fireplace inserts equipped with a water heat-exchange jacket:
- fuel combustion efficiency - up to 70%;
- reasonable cost (compared with brick structures);
- simple and quick installation;
- the fireplace stove equipped with a transparent door will fit perfectly into the interior of the living room.
Reference. Fireplace water fireplace "Thermofor Aquarius" with a heat transfer of 12 kW will cost 530 y. It is difficult to estimate the additional costs; their value depends on the method of decorating the fireplace. Budget option: put the heater on a solid base, connect it to the radiator network, and do the finishing yourself or put it off for later.
Cons of metal furnaces are similar to the disadvantages of furnaces:
- the fireplace quickly warms up and cools, it needs continuous circulation of the coolant;
- provides heat to a limited number of batteries;
- due to the temperature difference, condensation forms on the inner walls and soot deposits are deposited;
- a complete resemblance to a natural fireplace is achieved through design - decorative brickwork or plasterboard lining.
Using a fireplace insert as the main source of thermal energy, do not count on long burning from 1 bookmark. Example: the useful volume of the combustion chamber of the aforementioned “Aquarius” is only 62 liters, but it will not work to completely block the firebox with firewood. Have to throw logs every 3-4 hours.
Note. Most steel furnaces suffer from a similar drawback - in the intensive burning mode, only have time to toss firewood.
Strengths and weaknesses of brick heaters
Heat exchangers are installed inside the stove in two ways - in the firebox or gas duct, on the path of the hot combustion products. Each option differs in its nuances:
- the boiler in the combustion chamber quickly warms up under the influence of a flame, but forms condensate and soot on the walls;
- in case of boiling and steam formation, the tank may burst right in the firebox and break the brickwork;
- the heat exchanger inside the chimney swirls is much safer, but it heats up more slowly because it receives less heat.
Reference. The coil placed in the flue must have twice the heat transfer area than the boiler in a furnace that is comparable in power.
The main disadvantage of any brick heater is the high cost of materials and masonry work. Suppose you decide to save and put down the stove yourself. It will take experience, time and technical ability - it is not easy to start construction in the middle of an old house. The best option is to lay the foundation and the furnace at the stage of walling.
Why are stone stoves with a built-in heat exchanger appreciated:
- the service life is incomparably longer than any heat generator - at least 50 years;
- the ability to accumulate heat, to heat adjacent rooms for a long time after attenuation;
- maximum efficiency - 70 ... 75%;
- in a heated furnace, the soot formed on the walls of the tank and in the chimney well burns out;
- some brick stoves - a canal "Dutch", "Swede", a bell-shaped construction of Kuznetsov - can safely heat a two-story house.
Interesting fact. The water heater section can be added to any brick stove. Intelligent stove masters know how to change the layout and arrangements for installing a heat transfer water register.
Furnace Tips
Recommendation number one: use a solid fuel boiler to heat the coolant in the water heating network. If necessary, buy a long-burning model with a loading chamber volume of more than 100 liters. Modern TT-boilers direct 75-80% of the combustion energy to heat the water and almost do not raise the ambient temperature.
If for various reasons you want to install a furnace with a heat exchanger, listen to the following tips:
- A cast iron or steel potbelly stove is well suited for a small cottage with an area of 40-80 m². There will be enough heater for convection heating of the central room, arrange batteries in the neighboring rooms.
- A fireplace insert or an iron stove equipped with panoramic glass will be a successful decoration of the living room. One condition: use the product as an additional source of heat, and put the main load on a gas or wood heat generator. Then it will be possible to maintain cleanliness and order near the stove.
- At the stage of building a house, unambiguously lay a brick stove. This is the best option compared to iron heaters.
- Theoretically, the capacity of the fireplace insert is enough to heat a square of 100-120 m². Practice shows: without the help of a second heat generator it will have to be loaded with firewood with an interval of 3-4 hours. Therefore, expect a smaller heating area.
An important point. All wood-fired heaters equipped with a water circuit have one thing in common: due to the intense heat extraction, the surfaces of the register and the chimney wall are abundantly covered with soot. The only way out is to heat the stove at maximum so that the soot deposits burn out from heat. Supporting this mode is not always convenient.
How to choose the design and calculate the area of the heat exchanger in the brick version of the furnace:
- If the register is inside the firebox, 1 m² of its area is able to transfer water up to 10 kW of heat. Example: you need to heat rooms of 80 squares - it will take about 8 kW of energy and a heat exchange surface of 0.8 m².
- The chimney coil is not so effective. Expect 400–500 W heat transfer from 1 m² of register.
- For the convenience of cleaning, it is better to make the boiler flat - in the form of a tank with inlet pipes. Ribbed constructions made of round pipes are harder to clean. For installation inside the flue, weld the register from the profile pipes.
- The heat exchanger material is low-carbon steel of the grade St10 ... St20 with a thickness of 4-5 mm. It is allowed to use heat-resistant and stainless steel 2-4 mm, but it must be boiled in an inert gas - argon.
- Using pre-cast iron batteries is strongly discouraged. Reasons: the metal cracks from temperature shock, and the seal between the sections will burn out over time, a leak will appear.
Tip. Do not overstate the heat transfer area of the “in reserve” circuit. The furnace body will receive much less heat, and the water in the register can overheat and boil. Do not lay pipes made of corrugated stainless steel in the chimney - its real area and workmanship are difficult to determine.
Heat exchanger connection diagrams
In the framework of this publication, we will not describe the methods of making stoves, but immediately proceed to the strapping. If you want to make a water heater yourself, we recommend that you read the individual manuals:
- homemade heater for a solid fuel garage and mining;
- instructions for fireplace and stove masonry;
- diagram and order of the hob with a boiler.
If you purchased a factory oven with a heat exchanger, carefully read the attached instructions. The documentation always indicates the diameters of the pipes and methods for connecting the water circuit to the heating devices.Usually 2 schemes are applied:
- An open system with gravitational (convective) heat carrier flow.
- Closed radiator network with forced movement of water from the pump.
Note. Gravity circuits often use bypass pumps. The goal is to reduce the temperature difference between the supply and return, increasing the coolant speed and heating efficiency. In the absence of electricity, the system will continue to operate in gravitational mode.
Gravity flow is organized by increasing the diameters of highways and slopes of horizontal sections. The minimum cross-section of the distributing collector in the gravity scheme is 32 mm (an inch and a quarter), the slope is 3 ... 5 mm per 1 running meter. An open expansion tank is at the top point, all the air entering the system goes there.
With the closed circuit shown in the figure above, the coolant is under pressure (at least 1 bar “cold”) and moves under the pressure of the pump. The diaphragm expansion tank is located at the bottom point and is connected to the return line through a shut-off valve. The installation of a safety group with an air vent, pressure gauge and relief valve is mandatory.
Tip for choosing a scheme. When buying a stove for a house with water heating, the homeowner obviously relies on the autonomous operation of the system. Hence the conclusion: a gravity-flowing scheme is best suited for working with a hot-water oven. After turning off the light, the circulation in the circuit will not stop and the heat exchanger will not burn out.
Conclusion
The option of combining water heating systems with furnaces cannot be called ideal. Moreover, we strongly recommend avoiding such schemes and installing normal boilers. The exception is special circumstances and living conditions, for example, power outages or buying a finished house with a wood stove, which already has a hot water circuit.