Product Overview & Application
The Defro Optima HG 25 kW wood gasification boiler is a manually fed central heating boiler designed for split logs and use in water-based heating systems. It is suitable for installations where firewood is used as fuel and the generated heat is integrated into the heating system via a buffer tank.
The boiler is intended for closed hot water heating systems and operates with a maximum flow temperature of 90 °C. The 25 kW output makes it a suitable solution for appropriately designed wood heating systems, although the specific boiler selection should always be based on the heat load and system design.
Technology & Equipment
The Optima HG operates on the wood gasification principle. The split logs are degassed in the upper combustion chamber; the wood gases are directed through the combustion nozzle into the lower combustion chamber where they are burned off. Heat transfer occurs via the boiler body with a water jacket and the tube heat exchangers.
Equipment includes an electronic control unit, an induced draft fan, fireclay bricks in the combustion chambers, a combustion nozzle, turbulators, and a cleaning mechanism for the heat exchangers. A safety temperature limiter cuts the power supply to the fan if the boiler temperature exceeds the specified limit range.
Everyday Advantages
The wide filling door makes it easier to load split logs, while the separate arrangement of the filling, combustion chamber, and ash doors facilitates access for cleaning and maintenance. The sight glass allows visual inspection of the gasification flame without unnecessarily interrupting the combustion process.
Through the intended operation with a buffer tank, the generated heat can be stored temporarily and released to the heating system as needed. This supports smooth system operation and helps integrate the heat from log burning effectively into the overall system.
System Integration & Compatibility
The Defro Optima HG 25 kW is designed for integration into closed heating systems according to DIN 12828. A heating buffer tank is required for operation; additionally, a functioning return temperature boost with a sufficiently high return temperature is necessary to protect the boiler body from low return temperatures.
The hydraulic integration, system safety equipment, and connection to the flue gas system must match the specific installation. The chimney, safety valve, expansion vessel, return temperature boost, and thermal safety device must be professionally designed as part of the system planning.
Technical Specifications at a Glance
The following technical data refers to the Defro Optima HG 25 kW variant.
| Rated Output | 25 kW |
| Fuel | Split logs / hardwood, residual moisture 12–20% |
| Combustion Technology | Wood gasification |
| Efficiency | 92.2% at full load |
| Energy Efficiency Class | A+ |
| Max. Flow Temperature | 90 °C |
| Max. Operating Pressure | 3.0 bar |
| Boiler Class | Class 5 according to EN 303-5 |
| Draft Requirement | 16 Pa |
| Flue Gas Temperature | 127 °C |
| Flue Pipe Connection | Ø 130 mm |
| Safety Heat Exchanger | Yes, built-in |
| Buffer Tank Recommended | Yes, required for operation |
| Height | 1460 mm |
| Width | 620 mm |
| Depth | 1155 mm |
| Voltage | 230 V |
| Frequency | 50 Hz |
| Fuse Protection | 3.15 A |
| Power Consumption | max. 35 W |
| Phases | 1N |
Installation
The boiler must be installed by qualified professionals in accordance with applicable regulations and manufacturer specifications. The boiler is intended for closed heating systems and requires a professionally designed hydraulic system with a buffer tank, return temperature boost, safety devices, and suitable water quality.
Before connecting to the flue gas system, the chimney cross-section, chimney draft, and installation conditions must be professionally checked. The electrical connection of the control unit is designed for 230 V / 50 Hz and may only be carried out by appropriately qualified personnel.
Notes
The intended fuel is hardwood in split log form with suitable residual moisture. Other fuels or unsuitable materials must not be used. For proper operation, the specifications regarding return temperature, buffer tank, cleaning, maintenance, and chimney draft must be observed.
The output specification serves for the technical classification of the boiler and does not replace a heat load calculation. For planning, commissioning, flue gas measurement, and maintenance, the complete manufacturer documentation and locally applicable regulations should be considered.
Scope of Delivery
- Defro Optima HG 25 kW wood gasification boiler
- Installation and operating instructions
- Warranty card
- Electronic control unit
- Induced draft fan
- Analog boiler thermometer
- Cleaning mechanism for heat exchanger cleaning
- Filling and combustion chamber lining
- Combustion nozzle
- Cleaning tool
- Built-in safety heat exchanger
- Turbulators
