More about De Twaalf Ambachten
Green Techniques
Handbooks and products

McMullin & Co
Florence Diemont


Beter 1 x zien...

Better wood stoking

We had more than enough time for experimentation during the bitter cold winter of 1995-96. Always in search of improvement and innovation, we were looking for a faster and better way of stoking our Finn-ovens, an oven that build-it-yourselfers had been casting in our workshop for the past 11 years. At that time, we advised people to use two loads of wood, weighing 3 to 3.5 kilos per load, for this large, counterflow channeled Finnish oven. If you wanted 12 hours of heat, for instance, you had to burn around 7 kilos of wood; however, as the fire inside the oven grew larger and more intense, it began to splutter, as if the fire was 'chewing the air'. We fixed this problem by installing a chrome plate above the air vent. The spluttering stopped and the fire not only burned smoothly, it burned hotter too. At the time, we concluded that the improvements resulted from an improved air stream. But does that make sense?

Recently we received an informative letter from Fetze Tigchelaar, a Friesian tile-stove maker, who brought to our attention an alternative and, in his opinion, better method for stoking fires. In short Tigchelaars method is as follows: He burns the wood in his stoves from top to bottom, a reversal of the traditional manner of stoking fires that, as Tigchelaar found, results in the gradual releasing of the gases contained in wood. If, however, you burn wood in the traditional manner, that is from the bottom up, the wood gases are not released gradually and this causes the fire to splutter.



Tigchelaar wrote that he had arrived at this new stoking method through his dicussions with Finnish architect and researcher Heikki Hyytiäinen, who had published a book about Finn-ovens in the 1980s. Financed by the European Union, Hyytiäinen undertook a research project on stoking fires that produced some remarkable findings about the 'top down' method of fire stoking. Indeed, if wood gases are released too quickly, the wood will burn explosively, and this is especially true in tile stoves that have so-called 'contra-stream channels' (as all Scandinavian stoves have), the wood (kindled from below) beginning to splutter as soon as it starts to burn.




Inspired by Hyytiäinen's findings, we molded a chrome steel plate into a step-like shape, raising and narrowing it to 10 cm. The wood we burn in our self-made Finn-oven is approximately 25 cm long. The step leads to a platform that is located at least 16 cm inside the oven, where the wood is placed on its end, upright. We light a kindling fire on the platform and/or on the top of the wood itself, and this kindling fire ignites the upright standing wood. Then all the wood (now the full load of approximately 6 kg maximum at one time!) burns in a downward direction, which, crucially, allows the wood gas to be released gradually. Because we only need to 'load' the stove once, the preparatory stoking process is shorter. The stove does not burn out prematurely, and the burning process is significantly hotter in its final stage. This new 'top down' wood stoking method can also be used in smaller (self-made) tile stoves, which also have counterflow channels.



In our 'standard tile stove' we achieve a similar effect by lighting the kindling fire against the horizontally stacked wood. Because these stoves have deep chambers, capable of accomodating 80 cm long pieces of wood, we burn from front to back, which also allows the wood gases to be released gradually. In all of our stoves we burn wood on an ash shaft, according to the 'Grundofen' principle. Fetze Tigchelaar concludes that both the wood stoker and the environment benefit from this 'top down' method of stoking wood. And we couldn't agree with him more!

During experiments in later years with the standard tile stove we have discovered that when we reverse the direction of combustion we get the high temperatures and very low smoke production which are characteristic of this new right way of stoking. So the drawing as shown here is not correct! The kindling fire should not be situated against te stoke door, but against the back side of the combustion chamber. The stacked wood should be brought in the chamber as soon as the kindling fire is lighted. The airstream coming from the damper will cool the wood to the spot where it burns and this cooling will prevent premature escaping of wood gas and so loss of heat potential.