5 Correct quantity of wood
When not much heating is needed, only place a small amount of wood in the boiler
Absorbing all the heat from a boiler fully loaded with wood would require buffer storage tanks larger than needed for
winter operation and also larger than those normally installed. When less heat is required, i.e. for hot water in the
summer, or during the evening shortly before the night set-back, only load the boiler with the amount of wood actually
needed. The table below displays the amount of wood needed for summer operation for different boiler sizes (= fuel
chamber capacity), wood type, buffer volume and buffer charging status. Bear in mind that a "buffer top" temperature
sensor that is installed too low reduces the usable volume.
If the living space already needs some heating, start with the amount of wood indicated in the table below. To
establish the correct amount, approach the fully charged buffer state slowly, adding one or two more logs every
heating cycle. If too much wood is loaded, an emergency shutdown of the boiler will occur. If the boiler overheats,
the flow of air is stopped. The fire will go out, but the hot wood will continue to smoulder for a while. and the unburned
wood gas resulting from the lack of air can create tar deposits in the boiler and flue. If this occurs often, the boiler's
heat exchanger will become clogged with tar.
Observe the energy density of the fuel. The energy content of 50 litres of wood briquettes corresponds to
100 litres of beech wood or 150 litres of spruce.
The current buffer charging status is displayed in the control system in the boiler overview and on the buffer. It
is shown in percent and is the average of the three buffer temperatures (top, middle, bottom) between 30 °C
(=0%) and 80 °C (=100%).
Tab. 5-1: Correct quantity of wood
SH20 / SH30 Buffer charging status SH40 / SH50 / SH60
Maximum fuel load Size of buffer storage tank (litres) Maximum fuel load
Bri-
quettes
Beech Spruce 3300 2200 1650 1100
Bri-
quettes
Beech Spruce
90% 85% 80% 70%
85% 78% 70% 55%
1/4 80% 70% 60% 40%
1/4 75% 63% 50% 25% 1/4
70% 55% 40% 10%
1/2 65% 48% 30% 0%
60% 40% 20% 1/8 1/4
55% 33% 10%
1/4 1/2 3/4 50% 25% 0% 1/2
45% 18%
40% 10%
4/4 35% 0%
30%
3/4 25% 1/4 1/2 3/4
20%
15%
10%
5%
1/2 4/4 0% 4/4
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