ATTACK 20 SLX PROFI - wood gasification boiler

Product detailed description

ATTACK 20 SLX PROFI – wood gasification boiler with an output of 20 kW

ATTACK 20 SLX PROFI is a modern gasification (pyrolysis) wood boiler with a nominal output of 20 kW, designed for heating family houses, cottages, businesses and smaller industrial buildings where quality firewood is available. The SLX Profi range combines the proven cast-iron and steel construction of the ATTACK brand with controlled two-stage combustion technology, which achieves significantly higher efficiency and lower emissions than classic wood boilers with bottom or top burning. The ATTACK SLX Profi range is designed with an emphasis on a larger loading chamber volume and a longer interval between individual fuel loads, which is particularly appreciated when heating larger buildings or if you prefer less frequent refuelling. The larger combustion chamber also allows for storing longer logs, which simplifies fuel preparation.

The 20 SLX PROFI boiler belongs to energy class A+ and meets the current emission requirements (ecodesign) imposed on solid fuel boilers in the European Union. Due to the gasification principle, the firewood in the boiler is not burned all at once, but gradually – first it is gasified (pyrolyzed) in the upper loading chamber with insufficient air, and then the resulting combustible gas (a mixture of CO, H2 and hydrocarbons), together with the supplied secondary air, is perfectly burned in the ceramic combustion nozzle and lower combustion chamber at temperatures exceeding 900 °C. The result is a longer burning time per load of wood, higher efficiency (typically above 88 %) and substantially lower wood consumption per kilowatt-hour of heat produced compared to a classic boiler.

How wood gasification works and why it is more efficient

A common wood boiler with bottom burning burns fuel all at once with insufficiently controlled air supply, producing a large amount of unburned combustion products (tar, soot, CO) that escape through the chimney and clog the flue. The ATTACK 20 SLX PROFI gasification boiler, on the other hand, splits combustion into two separate phases taking place in two chambers, one above the other. In the upper loading chamber, the wood gasifies at a high temperature with a lack of oxygen (it is not directly burned), and the resulting combustible wood gas is forced by the combustion air fan through a ceramic (firebrick) nozzle into the lower combustion chamber. There, the gas mixes with secondary air and burns completely at a very high temperature. This process brings three main advantages: significantly higher combustion efficiency, minimal tar and soot formation (less cleaning, longer service life of the flue and chimney) and the possibility of smooth output regulation according to current heat demand, since the fan regulates the intensity of combustion instead of manual chimney damper adjustment.

Key features of the ATTACK 20 SLX PROFI boiler

• Wood gasification combustion with two-stage combustion and high efficiency above 88 %, energy class A+.
• Large loading chamber with a volume of approximately 95 l allowing a larger amount of wood to be loaded and a longer interval between refuelling.
• Turbulators in the heat exchanger – rotary turbulators increase the turbulence of flue gases in the heat exchange area, improve heat transfer to the heating water and reduce the temperature of the flue gases leaving to the chimney, thereby increasing the boiler's efficiency.
• Mechanical cleaning of the heat exchanger using an external lever/handle – the operator simply removes ash and soot deposits from the heat exchange surfaces with a few movements of the lever, without having to disassemble the boiler.
• Robust cast-iron/steel construction of the boiler body with increased wall thickness resistant to operational wear and thermal stress.
• Ceramic combustion nozzle and combustion chamber lining made of high-quality firebrick resistant to the high temperatures generated during wood gas combustion.
• Combustion air fan with output regulation ensuring an optimal air-to-fuel ratio under varying boiler loads.
• Electronic control with display and the option of weather-compensated control
• Large service door for convenient access to the combustion chamber, nozzle and heat exchanger for cleaning and maintenance.
• Safety heat exchanger / option to connect a cooling circuit against boiler overheating (we recommend adding a thermal safety valve in accordance with applicable Slovak legislation).
• Ready for conversion to automatic operation using the SL20968 kit for pellet combustion (COMBI Pellet), giving the boiler the option of fully automatic refuelling.
• Low emissions and compliance with ecodesign requirements for solid fuel boilers applicable in the EU.

Technical parameters of ATTACK 20 SLX PROFI

Differences between the Standard and Profi range

The 20 SLX PROFI boiler is equipped with the Profi range, which, compared to the basic Standard version, provides an electronic control unit with a clear display, more precise combustion air control via a motorized damper, and the option to connect a room thermostat or weather-compensated control based on outdoor temperature. Thanks to this, the boiler automatically adjusts its output to the current heat demand of the house, saving wood and extending the interval between refuelling. The Profi version also has thicker insulation on the boiler body, which reduces heat loss into the boiler room and increases operating comfort, especially during year-round operation.

Installation and commissioning

ATTACK SLX gasification boilers operate with a high flue gas temperature in the combustion chamber and are therefore sensitive to so-called low-temperature corrosion, which occurs if heating water that is too cold (below approximately 60 °C) returns to the boiler. During long-term operation with a low return temperature, acidic combustion products condense on the walls of the heat exchanger, which significantly shortens the service life of the boiler body. Therefore, we always recommend installing a mixing (three-way) circuit with a thermostatic head – for example ATTACK / Oventrop or ESBE LTC361 – in the heating system, which keeps the return water temperature to the boiler at a minimum of 60 °C until the boiler reaches operating temperature. This mixing circuit is also a condition for granting the extended warranty on the boiler body (see the Warranty chapter below).

Due to the nature of gasification combustion (the boiler works best at an output close to its nominal value), we strongly recommend supplementing the heating system with a storage tank (e.g. the ATTACK AK or AS range with a suitable volume according to the boiler output and the area of the heated building). A storage tank allows the loaded batch of wood to be burned all at once at optimal output, and the heat to be "stored" for later gradual use in the heating circuit throughout the day. Without a storage tank, the boiler output is frequently throttled, which increases tar formation, reduces efficiency and shortens the service life of both the boiler and the flue. Installation, connection to the flue, connection to the electrical network and initial commissioning should always be carried out by an authorised heating engineer/service technician in accordance with the project documentation, applicable legislation (in particular relevant technical standards and boiler room regulations) and the manufacturer's installation manual. Initial commissioning should be carried out by an authorised ATTACK service technician, which is also one of the conditions for claiming the warranty.

Fuel and its preparation

The recommended fuel for the ATTACK 20 SLX PROFI boiler is dry firewood (preferably hardwood – beech, oak, hornbeam) with a moisture content of up to 20 %. The moisture content of the wood fundamentally affects both the output and the service life of the boiler – wet or freshly cut wood (moisture content of 40 % or more) significantly reduces the calorific value, causes incomplete gasification, increased tar and soot formation, and can even cause the fire to go out. Wood should therefore be stored for at least 1–2 heating seasons under a well-ventilated shelter. The length of the logs should correspond to the dimensions of the boiler's loading chamber (usually up to approximately 50 cm), and the log diameter should be approximately 8–15 cm for even and smooth gasification.

Option of conversion to automatic operation – COMBI Pellet

If you are considering more convenient, automatic operation in the future without the need for daily wood refuelling, the ATTACK 20 SLX PROFI boiler can be subsequently converted to burn wood pellets using the SL20968 kit with a pellet burner with an output of 30 kW. This conversion kit is intended for ATTACK 20-35 SLX Profi boilers and includes a burner, a pellet hopper and the necessary control electronics, including connection to the existing boiler control. When ordering the conversion kit, the serial number of the specific boiler to which the kit will be fitted must be provided, so that the service technician can verify compatibility and prepare the correct components. After conversion, the boiler functions as a fully automatic pellet heat source, and depending on the version, the original wood-burning function can be retained as a backup (combined wood/pellet operation).

Maintenance and cleaning

Regular maintenance is key to maintaining high efficiency and a long service life of the ATTACK 20 SLX PROFI boiler. We recommend emptying the ash pan and the space under the grate depending on the intensity of heating, usually several times a week. Mechanical cleaning of the heat exchanger using the external lever should be carried out according to the operating instructions, ideally once a day during intensive seasonal operation – this will extend the interval between major service cleanings and maintain the boiler's declared efficiency. At least once a year (before the start of the heating season), we recommend having a comprehensive service inspection of the boiler carried out, including checking the door seal, the condition of the ceramic nozzle, the combustion chamber lining and the functionality of the fan and controls.

Frequently asked questions

Is a storage tank necessary for the ATTACK 20 SLX PROFI boiler?
It is not a legal requirement, but it is strongly recommended. A gasification boiler works most efficiently at an output close to the nominal 20 kW, so a storage tank allows a batch of wood to be burned all at once under optimal conditions and the heat to be stored for later use. Without it, the output is throttled, tar formation increases and the service life of the boiler is reduced.

What is the recommended moisture content of the wood?
The recommended moisture content of firewood is up to 20 %, which usually corresponds to wood dried for at least 1–2 years under a shelter. Wetter wood reduces efficiency and increases the risk of fouling the heat exchanger and chimney.

What is low-temperature corrosion and how can it be avoided?
It is damage to the boiler body caused by the condensation of acidic combustion products at too low a return water temperature. It is solved by installing a mixing (three-way) circuit that keeps the temperature of the water returning to the boiler at a minimum of 60 °C.

Can the 20 SLX PROFI boiler later be converted to pellets?
Yes, using the SL20968 conversion kit designed for 20-35 SLX Profi boilers, which adds a pellet burner and the necessary control electronics for fully automatic operation to the boiler.

What is the difference between the Standard and Profi range?
Compared to the Standard version, the Profi range offers more precise electronic control with a display, the option of weather-compensated control based on outdoor temperature, and usually thicker insulation on the boiler body, resulting in higher operating comfort and slightly lower fuel consumption during long-term operation.

Who is allowed to carry out the initial commissioning of the boiler?
Initial commissioning, connection to the flue and the electrical network should always be carried out by an authorised heating engineer or an authorised ATTACK service technician, in accordance with the installation manual and applicable legislation. This is also a condition for the validity of the warranty.

What flue pipe diameter does the boiler require?
The ATTACK 20 SLX PROFI boiler is standardly equipped with a chimney connection with a diameter of 180 mm; however, the exact chimney draught and diameter must be assessed individually according to the height and type of chimney (we recommend consulting a chimney sweep or a designer).

Why choose the ATTACK 20 SLX PROFI

ATTACK is a Slovak boiler manufacturer with a long tradition and an extensive service network throughout Slovakia, which is a great advantage when heating with solid fuel – spare parts (ceramic nozzles, seals, fans, control units) are readily available and service is not dependent on imports from abroad. The 20 SLX PROFI boiler is designed to last decades of operation provided the recommended conditions are met (protection against low-temperature corrosion, quality dry wood, regular maintenance). The combination of cast-iron and steel components, ceramic combustion chamber lining and well-thought-out mechanical heat exchanger cleaning is among the proven solutions tested in practice over the years, appreciated by both installation companies and end customers in everyday operation.

When selecting the output of the 20 SLX PROFI boiler, be guided primarily by the heat loss of the heated building calculated according to the applicable standard (EN 12831), not just approximately according to the floor area of the house. An undersized boiler cannot cover the heat loss on the coldest days, while on the other hand a significantly oversized boiler operates more often at partial output, which, in the case of solid fuel boilers, reduces efficiency and increases tar formation. If you have any doubts about the correct choice of output, we recommend consulting a heating designer or directly an ATTACK sales representative.

Emissions and environmentally friendly operation

Thanks to two-stage controlled combustion and a high operating temperature in the combustion chamber, the ATTACK 20 SLX PROFI boiler achieves significantly lower emissions of particulate matter, CO and organic compounds compared to classic wood boilers with bottom burning. The boiler meets the requirements of the Ecodesign Regulation (Directive 2009/125/EC and related implementing regulations) imposed on solid fuel boilers placed on the market in the EU. Lower emissions also mean fewer deposits in the chimney and flue, which reduces the risk of soot fires in the chimney and extends the interval required between chimney sweep cleanings.

Warranty

The manufacturer provides a standard warranty of 36 months from the date the ATTACK SLX wood gasification boiler is put into operation, but no more than 42 months from the date the boiler is shipped from the factory. If protection against low-temperature corrosion is installed (a mixing circuit maintaining a return temperature of at least 60 °C), an extended 7-year warranty on the boiler body can be claimed. For the warranty to be valid, initial commissioning must be carried out by an authorised ATTACK service technician and the prescribed method of operation must be observed (in particular fuel moisture content and protection against low-temperature corrosion). Exact warranty conditions can be found in the warranty card supplied with the boiler.