4 Vitolig 200
The rated boiler output will only be
achieved with dry firewood (25 %
moisture content). Firewood of poor
quality or with a high moisture content
reduce the rated output and the length
of combustion.
Logs should ideally be 45 to 55 cm long.
Older firewood of 25 to 33 cm length
should be cleanly stacked, otherwise
holes will be burned into the wood,
which reduces the output and leads to
tar deposits.
Approx. 44 % more softwood is
required for the equivalent energy yield
as for hardwood.
32
4.3 Fuel
Split logs
The calorific value of firewood depends on its water content
Wood condition
Water content (w)
Calorific value (Hu)
Freshly cut
50 60%
2.0 kWh/kg
Dried over a summer season
25 35%
3.4 kWh/kg
Dried for several years
15 25%
4.0 kWh/kg
Comparison between softwood and hardwood
Calorific value
with water
content of
w = 20%
Raw density
Energy/m
3
Softwood (e.g. common
spruce)
4.1 kWh/kg
0.43 kg/dm
3
1.763 kWh
Hardwood (e.g. beech)
3.9 kWh/kg
0.65 kg/dm
3
2.535 kWh
Conversion table for assorted common firewood
Unit of measure
Assorted
Solid measure
of timber
(smt)
Round timber
Stacked cubic
metre of
timber
(stcm)
Stacked
cubic metre
of timber
(stcm)
Tipped cubic
metre of
timber (tcm)
Tipped cubic
metre of
timber (tcm)
Tipped cubic
metre of
timber (tcm)
(
)
Split logs
Firewood pieces
Chippings
stacked
tipped
G 30 "fine"
G 50
"medium"
1 smt round timber
1
1.40
1.20
2.00
2.50
3.00
1 stcm split logs
1 m long, stacked
0.70
1
0.80
1.40
(1.75)
(2.10)
1 stcm firewood pieces
boiler−ready, stacked
0.85
1.20
1
1.70
1 tcm firewood pieces
boiler−ready, tipped
0.50
0.70
0.60
1
1 tcm (forest) chippings
G 30 "medium"
0.40
(0.55)
1
1.20
1 tcm (forest) chippings
G 50 "medium"
0.33
(0.50)
0.80
1
Wood briquettes
Only wood briquettes acc. to
ÖNORM M7135 may be used:
H
Diameter between 40 and 120 mm.
H
Max length 400 mm.
H
Raw density min. 1 kg/dm
3
.
H
Water content w less than 10%.
H
Calorific value 5 kWh/kg.
Chippings
Chippings should provide a length of at
least 5 cm and a minimum diameter of
3 cm. Therefore, chippings G30 (fine) and
G50 (medium) can be used.
Calorific value with a water content of
w = 25%:
H
Softwood: 3.8 kWh/kg
H
Hardwood: 3.6 kWh/kg
5822241 GB
