Tips for clean biomass burning

For biomass heating systems, the choice of fuel is the first priority. The right fuel is crucial for a clean and efficient combustion process. Wood should be dried for at least 2-3 years to maintain a moisture content below 25%. If you use wood that has been stored for a shorter period of time or is moist (more than double the wood moisture), about one fifth of the energy stored in the wood is lost during combustion for the additional evaporation of water. Even if the biomass boiler is operated incorrectly, more than half of the fuel energy can be lost through the chimney despite dry wood. The resulting additional demand for firewood in the case of incorrect operation or the use of excessively moist wood turns the inexpensive fuel into an expensive energy source. Correct heating is therefore achieved with dry wood, pellets or wood briquettes. Not suitable for the stove are treated wood, disposable boxes, chipboard, wood waste from construction sites or joineries, cardboard and waste paper.

Burning packaging material, treated wood (impregnated or varnished), chipboard, plastic or other household waste is prohibited by law and can lead to loss of the manufacturer’s warranty!Even wood from construction sites and joineries that appears to be natural can be treated with wood preservatives and is not suitable for burning in your own oven as poisonous smoke and ashes contaminated with pollutants are produced.Printed paper is NOT suitable for lighting! Burning printer’s ink and coatings releases pollutants and the ash hinders the draught. Dispose of your paper waste in the designated collection container.The quality of a fuel is important for low-pollution and efficient heating. With purchased fuels, however, the quality is often not directly apparent. There are, however, some clues to help you judge the quality of the fuel:

Firewood:

Pay attention to the moisture content of the wood. This should not exceed 25%, values below 20% are favourable. You can check the moisture content (directly after splitting a log) with a commercially available wood moisture meter. The wood must be clean and free from decay fungi. The logs should be of equal length. When measuring the length, make sure that the wood fits well into the combustion chamber of your stove.

Wood briquettes:

They should be made of untreated wood (with small additions of natural binders if necessary). The stated calorific value should be 5 kWh/kg (or 18 MJ/kg) or higher. If the manufacturer states that his product complies with the EN 14961-3 standards, he assures them of high quality in terms of chemical speciation, calorific value, moisture and ash content. In the absence of clear information on the biomass chemical analysis and on compliance with a quality standard, the use of other raw materials cannot be excluded (e.g. residues of treated wood materials, chipboard, cardboard …) and this would lead to higher pollutant emissions and/or lower calorific value. Obvious defects would be crumbling briquettes, a high ash content or a very fast combustion, which you would notice when comparing different briquettes.

Wood pellets:

The requirements are largely the same as for wood briquettes. The new European product standard is EN 14961-2 and the highest quality class defined therein is “A1”. In addition to the quality standard for the fuel, there is the ENplus certification system, which certifies the manufacturer or its production chain. With ENplus, an independent body checks that the manufactured product actually meets the product standard. High-quality pellets guarantee a long-term trouble-free operation of your heating system.