38
3.7 Recommended fuels
Wood and wood briquettes. We recommend the use of split hardwood that has been stored outdoors under
cover for at least 1 year. Wood that has been stored indoors has a tendency to become too dry and will burn
too quickly. We recommend that you fell the wood during the winter when a lot of the moisture in the wood
will have been drawn down into the roots. In order to achieve optimum combustion, the wood’s moisture
level should not exceed 18 %, which roughly corresponds to storing the wood under cover outdoors for one
year. The moisture level of the wood can be measured using a moisture meter or by applying dishwashing
liquid to one end of the log and blowing air in the other end. If the wood is dry enough, soap bubbles will
appear. The wood should be chopped into logs with a diameter of approx. 10 cm and a log length of max. 39
cm. Firing with wet fuel will reduce the energy efficiency and increase the particle emission.
Burning varnished wood, impregnated wood, chipboard, paper, and other waste is strictly forbidden. Burning
these materials will damage the environment, the wood burning stove, and your own health. Fossil fuels
must not be used.
4. The chimney
The optimum combustion is achieved at a constant chimney draft of 10-14 Pascal (Pa) measured in the flue
pipe above the stove (when having a smoke exhauster). However, with natural draft (chimney without smoke
exhauster) the draft in the chimney will be between 18-25 Pa when conditions are optimum. There are many
factors that affect the chimney draft, including the outside temperature, wind strength, and surrounding
buildings. There are no requirements with respect to specific chimney heights, but a chimney must be tall
enough to provide a good draft. If the recommended chimney draft is not achieved, there may be problems
with smoke out of the door by firing.
Data for chimney calculation
Wood
Flue temperature at [20°C]
245
Chimney draft at testing power [mbar]/[Pa]
0.12 / 12
Flue gas mass flow [g/s]
5.7
4.1 Inadequate draft in the chimney
If you experience poor draft in the stove after the installation, please make sure that there is nothing in the
chimney to restrict the smoke and that no nearby buildings or trees affect the winds around the chimney.
If the chimney is too short, leaks, or is inadequately insulated, there may be problems with the chimney draft
(let the chimney sweep assess this). The draft should be sufficient during the ignition phase when the
stove/chimney is cold to provide a clean combustion and prevent smoke leakage. Therefore, we recommend
a chimney draft around 5 Pa in the ignition phase.
Once the ignition is a success and the smoke temperature is rising, it is important that the chimney draft
reaches a stable area around 18-25 Pa in operation (1 hour after ignition) when the chimney/stove is hot.
The draft in the area of 18-25 Pa when the stove is hot is essential in order to achieve an optimum and clean
combustion. Therefore, we recommend that you measure your chimney draft when the chimney is cold and
when it is hot after 1 hour in operation.