How clean are wood central heating systems?

Heating with logs, wood chips or pellets is - despite critics - very environmentally friendly. However, fireplaces, tiled stoves and room stoves can be a problem. In these, combustion is uncontrolled - and the operators often fire up incorrectly.

It is undisputed: Heating with the renewable raw material wood - be it in a pellet, wood chip or lump wood heating system - is more climate-friendly than burning fossil fuels such as oil or natural gas. Because while the use of (preferably regional) wood keeps the carbon cycle in balance, burning oil or gas releases millions of years of bound CO2.

Nevertheless, the question is justified: What emissions are produced when wood is burned?
The answer: mainly carbon dioxide and carbon monoxide, small amounts of nitrogen oxides and organic hydrocarbons, as well as ash, soot and smoke containing fine dust.

The quantities of these substances, some of which are harmful to the environment, depend on numerous factors: Well-prepared, dried and stored wood burns significantly cleaner than wet, dirty wood - and in modern wood-fired central heating systems, logs, chips and pellets burn particularly efficiently and with low emissions, since combustion is monitored by probes and precisely controlled by electronic systems.

Wood central heating systems are clean

Studies conducted by the Technology and Promotion Center for Renewable Resources (TFZ) in Straubing, Bavaria, at the end of 2022 prove this: Modern wood-fired central heating systems, regardless of whether they are fed with high-quality lump wood, wood chips or pellets, emit such low levels of particulate matter that chimney sweeps can hardly measure them. Modern wood-fired central heating systems also not only comply with the legal limits with regard to gaseous emissions produced during the combustion of wood, but often fall well below them. Nevertheless applies, as with all heating systems: Professional service, not least regular checks by the chimney sweep, ensures that the wood heating system continues to work as cleanly in its advanced age as it did when it was purchased.

Fireplaces, room and tile stoves

In terms of particulate emissions, classic room and tile stoves, wood-burning stoves and fireplaces are significantly more critical than wood-fired central heating systems. The reason for this is that they do not have any technical equipment for optimum combustion control, are rarely serviced, and the dimensions of the components (fireplace, Stack, air supply) are often inadequately matched to one another. In addition, quite a few operators already make mistakes when lighting the fire.

Always light the fire from the top
Because in addition to using clean, dry wood, proper lighting is crucial for the cleanest possible combustion. In combustion systems with top burn-off, in which the exhaust gases from the firebox are drawn off upwards, the stack of wood must always be lit from the top! In this way, the wood burns gradually from the top downwards, the burn-off is slower, more controlled and thus more efficient - and the flue gases flow through the hot flame, burning out almost completely.

Here's how it works: Set up a "cross-beige" - the thicker logs at the bottom, the thinner logs above. On top, place a lighting module made of thin fir wood sticks, equipped with a lighting aid (e.g. wood wool soaked in wax) and ignite. Usually a single match is sufficient - and the fire is already burning. Never use newspaper or other printed paper, as printing inks usually contain heavy metals.

Electro fine dust separator
And who would like to do still more concerning fine dust emissions, can retrofit its Stack comparatively simply and economically with a (electrostatic) fine dust and/or particle filter. Information and advice on this can be obtained from chimney sweeps and specialized companies.

It pays to be well informed
More information on the subject of "Clean heating with wood" is available at www.holzenergie.ch .