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Combined boiler for wood and pellets

The ATMOS DC18SP, DC25SP, DC30SPX, DC32SP combi boiler series enables ecological wood burning on the principle of generator gasification in combination with a pellet burner. The boiler allows changing fuels, manual wood heating and fully automatic pellet heating. If necessary, it is of course possible to buy a boiler without a burner, provided that the customer buys it later or uses it from the last boiler.

The boiler is designed as a body with three chambers placed one above the other. The upper two chambers are used to gasify wood, as we know it from classic gasification boilers, which we produce as standard. The third, lowest chamber is fitted with the required burner at the front and lined with ceramics for optimal combustion quality. Combustion systems are separated from each other by a water jacket, so they do not affect each other too much, and thus the boiler achieves high efficiency in heating with individual fuels. The flue gas discharge into the chimney is solved by one outlet, so we can do with one chimney.

  • Boiler efficiency from 88,9 to 92,5 %

ecolabeling Dotovany kotel

DCxxSP / SPX boilers meets 5th emission class (Energy efficiency class A+), Ekodesign.

Advantages of ATMOS boilers

  • possible combination of individual types of fuels – fuel change without modifications on the wood + pellet boiler
  • high efficiency for individual fuels – practically the same as for special pellet boilers (up to 92.3 % at rated output)
  • cheaper solution – if we add up the costs of acquiring two boilers, their connection and fume extraction (chimney), we find that one boiler, although more expensive, is more economically advantageous
  • small built-up area – compared to more boilers
  • one chimney and flue
  • ecological operation – boiler according to EN 303-5:2012 class 5, EKODESIGN 2015/1189
  • subsidized boiler
  • choice of door left / right
  • The boiler is equipped with the function of automatic start of the pellet burner after the wood has burned out





We recommend installing the boiler with Laddomat 22 or a thermo regulating valve with equalizing vessel 500 – 1000 litres. We also recommend installing the boiler with accumulating tanks of appropriate volume (e.g. 2000 litres), which allow utilising electricity for heat accumulation or connecting solar panels. If necessary, the boiler can be connected into a system without accumulating tanks. This comes into account if you use fuel oil.

Boilers regulation 

The operation of the boiler is fully automatic to heat up water to required temperature with high efficiency and in a good quality of burning. All this ensure:

  • HONEYWELL draught regulator
  • boiler (regulating) thermostat – fan control thermostat
  • waste gas thermostat
  • pump thermostat
  • main switch and changeover switch for boiler operation

Boilers and burners DCxxSP / SPX (in version Model 2018/2019) are equipped with the function of automatic closing or opening of the air supply to the boiler/burner (using the actuator) when heating with wood or pellets. The boilers are equipped with an AGF2 flue gas sensor and a KTF20 boiler water temperature sensor for function of automatic burner start after the wood burns out. Than the boilers are equipped with two KTF20 sensors (TV and TS) for controlling the burner with two temperatures on the accumulation tank. The whole set is sold in maximum equipment, for fully automatic mode and easy installation “plug and play”.



Boiler control panel with standard regulation

Panel composition:
Main off switch, safety thermostat, thermometer, regulator thermostat and combustion thermostat

Electro-mechanical regulation is an optimum solution for easy management of the operation of the boiler (ventilator). The design of the panel with standard regulation is a basic design for all produced boilers.

Regulace ACD 03

Each boiler can be equipped with a modern touch electronic control ATMOS ACD 03 for controlling the entire heating system depending on the outdoor temperature, room temperature and time. This regulation is able to control the boiler itself with a fan with many other functions.

Boiler control panel with equithermal regulation ATMOS ACD 03



Technical information

Drawing for DCxxSP / SPX boilers



 Description for DCxxSP(X) boiler drawing
1. Boiler body 25. Door filling – Sibral
2. Filling door (upper) for wood 26. Door sealing – cord 18 x 18
3. Ash-pan door (middle) 27. Heatproof shaped piece – half moon (door shield)
4. Exhaust fan 28. ATMOS A25 pellet burner
5. Heatproof shaped piece – nozzle 29. Primary air regulation
6. Control panel 30. Secondary air regulation
7. Safety thermostat (Caution – in overheat condition must be depressed) 31. Heat proof shaped piece – spherical space – (wood)
8. Air control damper 32. Heatproof shaped piece – back side of the spherical space – (wood)
9. Heat proof shaped piece – extension of the spherical space – (pellets) 33. Pump thermostat
10. Heat proof shaped piece – spherical space – (pellets) 34. Fuse (6,3A) T6,3A/1500 – H type
11. Sealing cord – nozzles – 12 x 12 35. Flue gas thermostat
12. Door for the pellet burner (bottom) 36. Changeover switch (wood-0-pellets)
13. Ignition (firing up) valve 37. End switch with button
14. Heatproof shaped piece – back side of the spherical space – (pelety) 38. Capacitor of exhaust fan – 1 μF
15. Cleaning lid 39. Sibral seal under the burner
16. Primary air screen 40. Measurement point for the combustion gases – flue gas analyzer
17. Ignition (firing up) valve pulling rod 41. BELIMO Actuator with the flap
18. Thermometer
19. Frame shield
20. Main switch with indicator light K  – the flue-gas duct neck
21. Flue gas brake (only DC30SPX) L  – the boiler water outlet
22. Draught regulator – Honeywell FR 124 M  – the boiler water inlet
23. Cooling loop protecting against overheating N  – filling valve pipe sleeve
24. Boiler (regulating) thermostat – fan control thermostat P  – sleeve for a sensor of the valve which regulates the cooling loop (TS 131, STS 20)


Boiler dimensions
A 1665 1665 1665 1742
B 757 957 957 957
C 643 643 643 678
D 1375 1375 1375 1448
E 150/152 150/152 150/152 150/152
F 65 65 65 70
G 207 207 207 184
H 1436 1436 1436 1507
CH 212 212 212 212
I 212 212 212 212
J 6/4″ 6/4″ 6/4″ 6/4″


Specification Boiler type
Rated power (wood) kW 20 27 30 35
Rated power (pellets) kW 4,5 – 15 6 – 20 6 – 20 6 – 20
Heating surface m2 2,5 3,3 3,3 3,8
Fuel shaft volume dm3 (l) 66 100 100 140
Filling hole dimensions mm 450 x 260 450 x 260 450 x 260 450 x 260
Specified chimney draft Pa/mbar 20/0,20 23/0,23 23/0,23 24/0,24
Max. working water overpressure kPa/bar 250/2,5 250/2,5 250/2,5 250/2,5
Boiler weight kg 435 531 537 596
Gas-outlet pipe diameter mm 150/152 150/152 150/152 150/152
Ingress protection of electric parts IP 20 20 20 20
Electric input – at start-up – pellets (max.)
– in operation – pellets (max.)
– in operation – wood
W 522(572) / 1042 (1092)
42 (92)
Efficiency over the entire performance range – pellets/wood % 92,5/90,1 91,2/89,9 91,2/89,9 91,2/88,9
Boiler class 5 5 5 5
Energy efficiency class A+ A+ A+ A+
Waste gas temperature at nominal output – wood °C 157 177 177 185
Waste gas temperature at nominal output – pellets °C 109 139 139 139
Waste gas combustion products flow weight at nominal output – wood kg/s 0,010 0,015 0,017 0,018
Waste gas combustion products flow weight at nominal output – pellets kg/s 0,008 0,010 0,010 0,010
Specified fuel (preffered) quality pellets with a diameter of 6 – 8 mm with a calorific value of 16 – 19 MJ.kg-1
Specified fuel dry wood with a calorific value of 15 – 18 MJ / kg-1, water content 12 – 20 %, diameter 80 – 120 mm
Maximum wood length mm 330 530 530 530
Combustion time at nominal output – wood Hours 2 3 2 2
Boiler water volume l 78 109 109 160
Boiler hydraulic loss mbar 0,22 0,23 0,23 0,23
Minimum buffer tank volume l 500 500 500 500
Connecting voltage V/Hz 230 / 50 230 / 50 230 / 50 230 / 50


The Pellet burner


The burners in the version for models DCxxSP / SPX) are equipped with the function of automatic closing or opening of the air supply to the burner, by means of an actuator, when heating with wood or pellets.

Prescribed fuel: quality wood pellets (white) with a diameter of 6 to 8 mm, a length of 5 to 25 mm and a calorific value of 16 – 19 MJ.kg-1.

Burner display: used to display the current status of the burner and to set its functions

Burner control: electronic control AC07X, which controls the operation of the external conveyor, two ignition coils and the fan according to the requirements of the boiler and the heating system. The electronics are protected by a boiler safety thermostat, a safety thermostat on the pellet supply to the burner, a fan speed sensor and a photocell for flame sensing. The burner operation is signaled on the electronic control display.

Fuel ignition: automatic by means of two electric ignition coils.

Basic burner functions:
Possibility to use two backup outputs R and R2 for different applications
Possibility of connecting four different sensors TS, TV, TK and TSV
TS – lower sensor on the tank
TV – sensor upper on the tank
TK – boiler sensor or middle sensor on the tank
TSV – flue gas sensor or solar panel

  • burner control according to two temperatures on the expansion tank
  • control of the boiler fan from the burner by means of a reserve output
  • control of the boiler pump from the burner by means of a reserve output
  • control of the solar system directly from the burner
  • automatic burner start after wood burning for DCxxSP / SPX boilers

Burners are able to burn only good quality white pellets from soft wood without bark ø 6 – 8 mm, lenght 10 – 25 mm with heating power 16 – 19 MJ.kg-1. Burners are not able to burn pellets with high caking property in the burning chamber. In such case it is needed to clean the burning chamber in period once a day.

For these burners are appropriate conveyors:

  • Auger pellet conveyor for burner ATMOS A25 – DA1500 lenght1,5 m and diameter 75 mm
  • Auger pellet conveyor for burner ATMOS A25 – DA2000 lenght 2 m and diameter 75 mm
  • Auger pellet conveyor for burner ATMOS A25 – DA2500 lenght 2,5 m and diameter 75 mm
  • Auger pellet conveyor for burner ATMOS A25 – DA3000 lenght 3 m and diameter 75 mm
  • Auger pellet conveyor for burner ATMOS A25 – DA4000 lenght 4 m and diameter 75 mm