Evaluating The Combustion Quality; Wood Moisture Content And Calorifi C Value; Storing And Drying Wood - HASE Akaba Mode D'emploi

19. Evaluating the Combustion Quality

The following characteristics can facilitate easy evaluation of the combustion quality:
- Colour and composition of the ash
If the combustion process is effi cient, the result is a fi ne white ash. Dark colouration
indicates that the ash contains charcoal residue; in this case, the burn-off phase was
incomplete.
- The colour of the fl ue gases emitted at the chimney pot
In this respect, the following applies: the more invisible the fl ue gases exiting the chim-
ney, the better the combustion quality.
During the transitional seasons (spring/autumn), outdoor temperatures above
16°C can impair the chimney draught. If a draught cannot be created at these
temperatures by rapidly burning paper or thin wood shavings (quick fi re), you
should refrain from lighting the stove.
20. Wood Moisture Content and Calorifi c Value
Rule of thumb: the more damp the wood, the lower the calorifi c value
The calorifi c value of the wood depends largely on the wood moisture content. The more
moisture the wood contains, the more energy expended to evaporate it during the combus-
tion phase; this energy is then lost. Thus, the more damp the wood, the lower its calorifi c
value.
An example: freshly cut wood has a moisture content of approx. 50% and a calorifi c value
of around 2.3 kWh/kg; in contrast, wood which has been effi ciently air-dried has a moisture
content of approx. 15% and a calorifi c value of around 4.3 kWh/kg.
Accordingly, if you burn very moist wood, you will have about half the thermal output with
the same quantity of wood. Furthermore, burning moist wood results in substantial soot
build-up on the fi re box window.
Moreover, when moist wood is burned, the resulting water vapour can condense in the
fl ue pipe or chimney. This can lead to a build up of shiny soot on the chimney or chimney
78
creosote. In addition, if the wood has a high moisture content, the combustion temperature
decreases, which prevents complete combustion of all the wood components and causes
considerable environmental pollution.
You can use a wood moisture meter to determine the residual moisture content of
your fi rewood.

21. Storing and Drying Wood

Wood needs time to dry. If stored properly, it will air-dry in approx. 2 to 3 years.
Saw, split and store the wood ready for use; this ensures rapid drying
because smaller pieces of wood dry better than larger, uncut logs.
Stack and store your wood logs in a ventilated and as sunny as possible
location, ideally facing south, and ensure that they are protected from rain.
Leave a hand's width between the individual piles of wood so that air
can fl ow between them and carry away any escaping moisture.
Do not cover your stacks of wood with plastic sheeting or
tarpaulins; otherwise the moisture cannot escape.
Do not stack fresh wood in a cellar or basement, since it
will rot rather than dry due to the lack of airfl ow.
Only store already dried wood in dry and well-
ventilated cellar or basement rooms.