V202 K UB

Extuna V202 K UB is a natural ventilating boiler for half-metre firewood burning. It uses reverse combustion for utilizing wood energy maximality. It is designed for long performance life. Easy-to-clean inside and simple operation makes wood burning convenient. In order to achieve a high combustion temperature, the combustion chamber in refractory ceramics is only made in our factor.

To achieve optimal effect, firewood requires moisture content of 20 %.

The convection section consists of vertical tubes which are preferred for solid fuel firing, and then ash cannot fold so easily on the convection area. They include turbulators which increases efficiency and makes it possible to adjust the flue gas temperature for various chimneys. Smoke outlet mounted at the backside is standard. Alternatively customer can also choose to order smoke outlet at the left or right side, and ash door at opposite side, which can be easily for cleaning inside of boiler.

Charge pump, draught door and even chimney fan are operated by control system automatically. The boiler has a built-in boiling security system, and it will shut off automatically after completing firing.

Useful information »

Download product sheet (PDF) »


Model Width (A) Length (B) Height (C) Bottom to flue height (D)
35 540 mm 1 050 mm 1 135 mm 870 mm
55 660 mm 1 050 mm 1 280 mm 1 010 mm
70 660 mm 1 050 mm 1 420 mm 1 150 mm


Technical Data

Model Effect Wood Length Wood Capacity Water Volume Recommended Accumulator Volume *Min Chimney Draught Weight
30-40 kw
500 mm 125 L 125 L 800-2.00 L 25 Pa 425 kg
50-60 kw
500 mm 180 L 150 L 2000-5000 L 30 Pa 485 kg
60-70 kw
500 mm 230 L 180 L 4000-6000 L 40 Pa 520 kg

The picture shows our standard model boiler. Connections can be designed and set up according to customers’ requirement when ordering. Manufactured according to manufacture standard 1999:4 paragraph 8
*Extuna manufactures custom-made accumulator tanks according to our customer’s specifications.


  • Draught gauge
  • Flue temperature measurement
  • Pressure and temperature measurement
  • Sweeping tools
  • Flue funnel
  • Turbulator
  • Overheating protection
  • Instruction


The boiler is very simple to use. Press the start button, put in firewood and light the fire. When the boiler is finished burning, the charge pump and draught door will be off automatically. Together with our good insulation, downtime losses reduce greatly. If, for some reasons, the boiler is approaching boiling point, draught door will be closed automatically (built-in overheating protection)


Natural ventilation is the most effective way of working for a domestic boiler. When the boiler produces a lot of gas, the gas velocity and flow increase greatly into the chimney. This creates a negative pressure in the combustion chamber, which increases air supply to the combustion. When the flame is moving towards its final stage (little amount of firewood left in wood burning room), the boiler produces significantly less amount of gas which provides a less negative pressure in the combustion chamber and the boiler “dragged” in less air. The result is that the boiler receives optimal air supply throughout the entire firing process. It is only possible with the natural ventilation and a well-controlled flue gas temperature.

If you do not have a chimney that meets the manufacturer’s recommendation for negative pressure, a flue gas fan shall be installed. Extuna provides several different models of fans.

Masonry chimney:
Whole stone x half stone (1 x ½)
35 kW
55 kW
25 cm (1)
12,5 cm
12,5 cm (½)
6 m
8 m
Round chimney: 35 kW 55kW
160 inside 6 m
180 inside 7 m 8 m
200 inside 8 m 8 m

Reverse combustion

Firewood in burning chamber

Firewood is dried



gases are produced


(primary combustion)

Secondary air

Gas combustion

(secondary combustion)

happens in the ceramic afterburner

wood boiler

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