The first step in selecting a solid fuel boiler is to determine the fuel type and combustion process technology (boiler construction). Previously, the customer decided on the availability of fuel and its storage, nowadays, technology and the related acquisition and operating costs play a major role in the decision-making process. Above all, the type of combustion and how the fuel is applied. Another factor influencing the decision-making can be fuel universality, ie the possibility of combining more types of fuel.
Before we completely analyze individual aspects of solid fuel boilers, it should be noted that boilers are subject to so-called emission classes, which have recently been radically tightened. Since 2018, emission class 1, 2 and 3 boilers should no longer be available. The future is therefore in class 4 and 5 boilers, which offer comfort comparable to gas and electric boilers. More about standards HERE.
The most important feature of the boiler is its ability to control the heating process, so as control over the supply of fuel and combustion air to the fireplace. The more the boiler itself is able to optimally control this process without operator intervention, the higher the prerequisite for better combustion. The combustion air supply can be:
- natural - the air supply depends on the chimney draft, which creates a vacuum in the fireplace and draws air into the fireplace
- forced - air supply is created and regulated by the exhaust fan. It represents more control over the combustion process.
The fuel supply is also divided into two possible ways:
- Boiler with manual stoking - fuel is added manually depending on the burning rate
- Boiler with controlled fuel supply - fuel is added automatically depending on the heat output
Solid fuel boilers make it possible to burn wood, pellets, coal or coke and are one of the cheapest heating options (in running costs) for households and business premises. Modern solid fuel boilers from the brands Atmos, Dakon, Viadrus are characterized by high efficiency and environmental friendliness. The advantages of traditional solid fuel boilers are low purchase and operating costs, on the other hand, the disadvantage is fuel handling and the necessary space for fuel storage, which can sometimes be inconvenient.
Use this type of boiler in buildings without gas supply, but for which higher comfort of operation is required. Wood boilers can be used not only as a main heating system, but also as an alternative to gas or oil heating.
Combustion process technology
This brings us to the explanation of the combustion technology itself. Today, you can choose from 4 technologies:
- afterburner boiler - in the boiler there is a gradual combustion of fuel and the flue gases pass through a layer of fuel (Figure 1).
- combustion boiler - in the boiler is progressive combustion and flue gases do not pass through the fuel layer (Figure 2).
- gasification boiler - a type of afterburning boiler with manual stoking, in which a higher level of combustion is achieved by controlled supply of combustion air by a fan (Figure 3).
- automatic boiler - boiler with automatic fuel supply and fan controlled combustion air supply (Figure 4).
The boiler with the most used and the most outdated combustion technology, which releases the most pollutants into the chimney. Regulation of power and the whole combustion process is considerably limited. The combustion air supply can only be controlled by opening and closing the air intake openings or the chimney flap.
The fuel is placed on the burning fireplace and the flue gases rise to the chimney mouth through new fuel, which gradually burns. Coke is the least polluting in this boiler construction. The coke-fired boiler reaches emission class 3, when lump wood and bituminous coal are burned, these boilers achieve emission class 2 and after 2022 it will no longer be possible to operate these boilers. Not suitable for brown coal.
Figure 1: Combustion boiler
The burn-out boiler produces slightly less pollutants. The boiler fuel is added to the space located above the fireplace. The advantage of this boiler is that the flue gases do not pass through the new fuel, maintain a higher temperature and are thus better burned. During combustion, the fuel is gradually fed into the combustion chamber, in which it burns on a sliding or rotating grate, and the flue gases in it are then removed off the new fuel. This boiler is suitable for brown coal with a higher content of volatile matter.
The burner boiler is in emission class 3 and should therefore be sufficient for the boiler operation after 2022.
Figure 2: Burn-out boiler
The difference with the above-mentioned boiler types is that the gasification boiler has an additional fan for controlled combustion air supply and can thus regulate the combustion process and output according to various requirements. And thanks to the much higher control of the combustion process, the volatile combustible contained in the fuel is substantially burned out, thus significantly reducing its amount which flows through the chimney. Gasification boilers thus convert solid fuel into gaseous fuel due to the high degree of volatile matter combustion.
The fuel is placed above the burner and the combustion of the gas is subsequently controlled by a fan. Boilers usually reach emission class 3, some already emission class 4 and 5.
Figure 3: Gasification boiler
Kotel Viadrus U32 - animation of a boiler operation
Source: Youtube channel ViadrusCZ
This type of boilers represents the most modern combustion technology. It is a solid fuel boiler with a tank that regulates the fuel supply (pellets or coal) to the fireplace and controls the supply of combustion air by means of a fan. The boiler therefore has various programs and these automatic activities are controlled by the boiler regulator. This means that only the minimum amount of fuel needed to meet the current central heating requirements can burn in the fireplace.
Automatic boilers belong to the emission class of boilers 3 and 4. However, if it uses pellets as fuel, it can reach the highest emission class 5.
However, the price of an automatic boiler is, of course, higher compared to conventional boilers. The price applies a simple rule, the smaller the possibility to control the combustion process, the simpler the fuel source and the cost. At a higher price, but you get better technology that will reduce your annual fuel costs.
Figure 4: automatic boiler
Subsidies for boilers
The aim of subsidies is nothing more than to support the transition of households to boilers with a higher emission class and thus help to protect the environment. Gasification and automatic boilers of 4th and 5th emission class bring higher purchase costs than old types of boilers. Previously it was possible to buy a boiler with manual stoking for 30.000 CZK, the prices of basic boiler designs corresponding to emission requirements are not lower than 35.000 CZK. Rather expect, but significantly higher price, subsidies for boilers up to 50 kW can be around 60,000 crowns. Subsidies then relate to the assembly and sale of brands of authorized manufacturers and suppliers.
The subsidy program of the Ministry of the Environment of the Czech Republic New Green Savings it is not the only subsidy program from which you can draw. Occasionally, it is also possible to obtain subsidies from some regions.
From time to time, regional authorities, in cooperation with the Ministry of the Environment, announce so-called subsidy calls, for the replacement of unsuitable manual-filled solid-fuel boilers.
Information on available programs can be found on the website of the State Environmental Fund in the section Grants and Loans.
Advice: Have the boiler selected by a specialist!
Finally, we recommend consulting the boiler selection with an expert, because you will find out best whether your boiler meets all the requirements (emission class, the required output for heating the building and others). And this is the moment when its come to why our site was actually created. We would like to give you the opportunity to find out all the necessary information in one place so that you can choose the boiler yourself, and if you would like advice, you can contact us at any time. We believe that the possibility of buying a boiler and ensuring the installation of the boiler, boiler inspection and boiler service in one place will save you a lot of time and energy.