10
6.3 - FIREWOOD
Wood is formed mainly by cellulose and lignite.
It also contains other substances, such as
resin (fir - pine), tannin (oak - chestnut) and,
obviously, a large quantity of water.
Good quality woods are oak, ash, beech,
maple and fruit trees, except cherry; medium
quality wood is: chestnut and birch; sufficient
quality wood: lime tree, poplar and willow.
Resinous trees are, normally, second-rate quality fuels.
Wood is therefore an extremely heterogeneous fuel,
due to different essences (beech, oak, fruit, resinous),
different moisture content, and due to different shapes
and dimensions.
Boiler operation will inevitably be effected by all these
factors. Especially by the log dimensions, the moisture
content and the way wood is loaded in the boiler.
6.4 - WOOD MOISTURE
The calorific value of the different types of
wood depends on their moisture content, as
illustrated in the table. Boiler output and auton-
omy will diminish as the moisture increases.
The table provides the power reduction factor
based on the moisture of the wood being used.
The heat output of the FIREX boiler is calcu-
lated for wood with a 15% moisture content.
As an example, wood which has been dried
for 2 years in a sheltered area has a 25%
moisture content.
Example:
moisture of the wood being used = 25%
output = nominal output x 0.86
6.5 - FIREWOOD DIMENSIONS
The dimensions, together with the moisture
content, contribute to determine the boiler’s
output. Small pieces (with a length, however,
conforming to indications indicated hereby)
are more easily flammable and therefore have
the tendency to increase the boiler’s output
and therefore to reduce its autonomy. Moreo-
ver, they fall with greater facility, in the lower
chamber, reducing the risk of the formation of
“bridges”. The so-called “bridge” is an empty
space in the firewood storage compartment, where un-
burnt wood logs remain. In this case the bed of embers is
not fed with continuity and the refractory burner’s slot is
uncovered. In these conditions, preferential air ducts are
created with a very small flame due to an excess of air.
The FIREX boiler must be fed with natural wood logs of
the length set out in paragraph 6.6. The log section must
normally be round (Ø approximately 10 cm).
6.6 - START-UP
Ensure the checks referred to in point 6.2
have been performed.
Close the bottom door and power the control
board (for the operation mode, see point 6.1).
Open the top loading door and place some
dry wood kindling crosswise on the main
stone, above the central slot.
Use highly flammable material on the wood, avoiding large
and square logs.
Light the wood using thin sheets of paper (newspaper or
the like).
The first ignition of the new boiler could be difficult due to
moist refractory cement casting.
Accordingly, we advise fully opening the primary air and
lowering the secondary air.
Close the upper door and wait a few minutes for the fire
to start and produce some embers (about 5 minutes).
After a few minutes, if looking through the flame sight glass
of the lower door you see that flame inversion is beginning,
add other larger logs.
Close the top door.
Press key
for 1 second, and the combustion phase
will start.
Correction factors for wood moisture
% OF
HUMIDITY
CALORIFIC
VALUE
kWh/kg
CORRECTION
FACTOR
15
20
25
4.50
4.18
3.87
1
0.93
0.86
CALORIFIC
VALUE
MJ/kg
16.20
15.05
13.93
