How to choose a solid fuel boiler?

Sooner or later, every homeowner faces the following questions: how to make the heating system as efficient as possible, which boiler is better to buy, how to choose and install heating equipment correctly?

Therefore, in this article, we propose to consider the most common mistakes when choosing solid fuel equipment:

1. Incorrect choice of heating method and fuel type

The characteristics of fuel for heating equipment are quite different, so its correct selection will help to save money as much as possible, and the equipment itself will maintain its performance for as long as possible.
The choice of fuel may depend on the consumer's financial capabilities, regional location (e.g., the presence of forests, coal mines, or the possibility of using woodworking and agricultural waste as heating materials), and the model of the equipment chosen (pellet boiler or manual loading).

The main types of fuel for solid fuel boilers are:

• Firewood
• Pellets (fuel pellets)
• Fuel briquettes
• Coal

Each type of fuel has both its pros and cons.

Firewood can be called a "classic" type of fuel. Their moisture content should be as low as possible. For heating purposes, it is very important that heat is released more slowly, but for a longer time. All hardwood firewood is best suited for this purpose, including oak, ash, birch, aspen, and alder.

The peculiarities of burning firewood of different types of wood are:

• Firewood from beech, birch, and ash is quite difficult to melt, but it can burn raw because it has low moisture content;
• Alder and aspen burn without forming soot, in fact, they even burn it out of the chimney;
• Pine trees give off more heat than spruce trees due to the higher amount of resin in their composition;
• Birch firewood is good for heat, but if there is not enough air in the boiler furnace, it produces a lot of smoke and forms resins that settle on the walls of the chimney;
• Oak and hornbeam have the best heat transfer during combustion and the lowest moisture content;
• Cedar forms long-smoldering coals;
• Coniferous firewood has low heat transfer, smokes, sparks, and forms resinous deposits, but melts easily;
• Although poplar and linden burn well, they burn out quickly.

The calorific value of firewood is the amount of heat that one unit of its mass releases when it is completely burned. It is measured in calories (units of heat). This means that one calorie is the amount of heat required to heat 1 g of water by one unit of °C (approximately 4.2 J). Of course, the more moisture in wood, the lower its caloric value. The caloric content of wet wood compared to dry wood (20% moisture) is as follows: moisture content of 30% reduces calories by 10-15%, and moisture content of 50% - by 35-40%. A freshly cut tree has a moisture content of 35-60%. It will be the lowest if the wood is harvested before the beginning of winter, preferably hardwoods such as oak and hornbeam. Wood should be harvested in advance. Thus, firewood that has lain under a canopy for a year before use will contain 20-25% moisture, and after two years this percentage will decrease to 13-17%. Thus, when heating a room with dry firewood, you can save on their quantity by about 2 times. The use of fuel with a moisture content of more than 20% leads to a decrease in efficiency and increases the need for more frequent cleaning of the boiler furnace and chimney from tar and sediment.

The amount of energy released during the combustion of 1 dm³of wood with a moisture content of 20% is shown in the table:

In general, one warehouse meter of dry hardwood can replace 200-210 liters of liquid fuel or 200-210 liters of natural gas.

Pellet - is a natural raw material of plant origin pressed under high pressure in the form of cylindrical pellets of standard size. The raw materials for its production can be bark, sawdust, wood chips, as well as other logging waste, agricultural waste (straw, sunflower husks, etc.), organic packaging materials, cardboard containers, etc.

The pellet production process consists of grinding, drying and pelletizing. The result is a lightweight, inexpensive, easy-to-store and absolutely safe fuel alternative to traditional fuels (firewood, coal, natural gas).

The advantages of using pellets include the following:

• Environmentally friendly, absolutely safe for the environment and humans. As a result, carbon dioxide emissions into the environment are 10-15 times lower and ash production is 15-20 times lower than when burning coal;
• Unlimited production (low-quality wood can be used);
• Easy transportation and storage;
• High calorific value (1.5 times higher than wood);
• Almost complete combustion with a minimum amount of waste, which means that the boiler can be cleaned much less frequently;
• The pelletizing equipment is regulated automatically;
• Pellet boilers operate longer, are more economical and require less maintenance.

The demand for this type of alternative fuel and solid fuel equipment that uses it is constantly growing.

Fuel briquettes are compressed wood waste (chips, wood chips), agricultural waste (straw, sunflower husks, buckwheat), and peat.

The binding agent in them is the natural polymer lignin (a substance that characterizes the lignified walls of plant cells). Briquettes are often used to heat private homes in various types of furnaces, wood boilers, fireplaces, etc.

Advantages of using fuel briquettes:

• A completely environmentally friendly product;
• They burn 2-4 times longer than wood;
• Ease of use;
• High calorific value (comparable to coal), about 2 times higher than that of firewood;
• Constant temperature at each stage of combustion due to an even flame;
• The ash content after combustion is minimal (1-3%).

Coal - is a combustible sedimentary rock of plant origin. The lowest calorific value of hard coal is on average 6000 kcal/kg, while for well-dried wood this figure is 3000 kcal/kg. Accordingly, to achieve the desired temperature, coal needs to be burned several times less than wood. Despite this advantage, coal has a high level of ash production (10-20%), which pollutes the environment. Another harmful component that coal emits is sulfur, which forms oxides when burned and turns into sulfuric acid in the air.

The main types of solid fuel boilers of TM "ALTEP" are shown in the table:

2. Incorrectly selected boiler capacity

One of the most important tasks when choosing solid fuel equipment is to correctly calculate the required boiler capacity. After all, if it is insufficient, the house will not be able to warm up sufficiently. If the power is higher than required, the cost of operating such equipment will be too high.

In order to correctly calculate the boiler's power, it is necessary to take into account:

• The area of the heated room;
• The volume of the heated room;
• Thermal conductivity of walls, windows, and doors.

You can calculate the power using the formula: P=k×S/10,

where P is the boiler power,
S is the heated area,
k is the heat loss coefficient.

For a well-insulated house (more than 15 cm of insulation; the roof, attic and basement are also insulated), k = 0.8.
For moderately insulated houses (5-10 cm of insulation; roof, attic, basement are insulated), k = 1.
For poorly insulated rooms or non-insulated rooms in general, this coefficient will be the highest - k = 1.2-1.5.
If the calculation is made for an apartment, k = 0.6 (provided that it is not the first or last floor) and k = 1.1 (if the attic or basement is poorly insulated).

Experts do not recommend choosing a boiler that has a power reserve of more than 20%, as this can lead to a decrease in efficiency.

3. Need for hot water supply (DHW)

Solid fuel boilers with a hot water circuit are so-called double-circuit boilers with a hot water supply system. The principle of their operation is not only to heat the room, but also to heat hot water for domestic needs. To obtain a sufficient amount of hot water, it is necessary to install an indirect heating tank with the required volume of water (heat accumulator). It provides inertia to the system, accumulates heat at the peak of the boiler's performance and transfers it to the heating and water supply system. This helps to stabilize the boiler operation and extends the period of its operation even when the fuel is burned until the next load.

It should be remembered that if you choose a boiler with hot water supply (DHW), its power should be at least 23 kW. Otherwise, such equipment will simply not be able to perform its functions. The correct selection of the boiler power together with the volume of the heat accumulator (buffer tank) will help ensure the uninterrupted and balanced operation of the entire heating system of your home.

4. Incorrect choice of heat exchanger area

If you are faced with the task of choosing a solid fuel boiler, pay attention to this criterion. It determines how much heat energy the equipment will transfer to the flowing coolant. Externally, boilers can look almost identical, while inside their design can differ significantly. If you have two boilers with the same capacity, give preference to the one with a larger heat exchange surface.

5. Steel thickness

To choose a reliable solid fuel boiler, be sure to pay attention to the thickness and steel grade of the heat exchanger. The durability of the equipment depends on this indicator. The heat exchanger operates at high temperatures, it is exposed to pressure, constantly contracts and expands, and when scale, soot and tar settle on its surface, the risk of corrosion increases.

If you need to choose a solid fuel boiler for a private house, opt for equipment with a heat exchanger wall thickness of 4-6 mm. This indicator is enough for the system to serve you for at least 10 years. You can intuitively determine it by the total weight of the equipment. If you have two models of the same power, you should give preference to the boiler that is heavier - accordingly, the thickness of the steel in it will be greater, which means it will be more reliable and durable.

6. Return coolant temperature

How to choose a solid fuel boiler for your home? In addition to power, steel thickness and heat exchanger area, you should also pay attention to the return temperature. It should be at least 57 degrees Celsius. Otherwise, condensation will form on the walls of the heat exchanger, which contains sulfuric acid. Over time, this will lead to corrosion.

To protect the equipment from low-temperature corrosion, it is equipped with three-way valves. The latter mix the hot coolant from the supply to the return.

7. Frequency of fuel loading

Another important point to consider before buying a boiler is the frequency of fuel refueling. Think in advance about how often you can add fuel to the furnace. Also note that some fuels burn faster, while others burn more slowly. In addition, the fraction and density of the fuel stacking affects the burning time.

If you can't be near the boiler all the time, go for equipment with a large combustion chamber or opt for a boiler with an automatic fuel supply. The larger the chamber volume, the less often you will have to refuel. You should also pay attention to boilers with automatic fuel supply. They are equipped with a spacious fuel chamber, and when fully loaded, such equipment can operate for a week without operator intervention.

Average frequency of fuel refueling for different types of boilers:

• wood boiler - when using wood, the burning period of one load is 4-6 hours, coal - 8-12 hours;
• long-burning boiler - 8-24 hours on one load of wood, 1-5 days on coal;
• mine-type equipment - firewood - 8-14 hours, coal - about 24 hours;
• pyrolysis - burns for 8-18 hours on a single load;
• pellet - one portion of fuel is enough for 3-5 days of burning.

Taking into account all the above characteristics, you will be able to choose a reliable boiler that will serve you for decades.

If you do not know how to choose a long-burning boiler or do not want to understand all the nuances, contact our manager or request a call on the website, and we will help you choose the equipment, taking into account all the important nuances for you.

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