Multifuel boiler + solar thermal: the dual-fuel setup for a Luxembourg project
Combine a multifuel wood + pellets boiler with solar thermal: up to €8,000 Klimabonus in Luxembourg. APS-phase guide for architects.
Why pair a multifuel boiler with solar thermal in Luxembourg?
A multifuel boiler burns logs and pellets in one unit. Combined with a solar thermal array, it becomes a full dual-fuel plant: solar covers DHW in summer, pellets take over in deep winter, and logs give a cheap top-up in shoulder seasons.
- Autonomy: three energy sources instead of one for a rural site
- Cost: solar cuts winter pellet use
- Subsidy: +€1,000 Klimabonus bonus and +15% with a buffer tank
- Resilience: a fallback fuel if one supply chain breaks
How do logs, pellets and solar fit on one project?
The multifuel boiler accepts hand-loaded logs and auto-fed pellets. A 500–1,000 L buffer tank smooths combustion and stores solar input. The solar array (3–6 m² for a house) feeds DHW and preheats the boiler return.
- Logs: manual top-up in autumn and spring, low running cost
- Pellets: automatic combustion at full heating load, tight control
- Solar: DHW from March to October, heating boost in shoulder seasons
- Buffer: 500–1,000 L sized to boiler output (mandatory for the bonus)
How much does Klimabonus 2026 pay?
Klimabonus 2026 targets pellet boilers. Plain log boilers are excluded: only the pellet side of a multifuel unit unlocks the grant. Amounts depend on building type and configuration.
- Single-family home: up to €8,000 (€4,000 without an old-system replacement)
- Multi-family building: €6,000 per unit, capped at €40,000
- District heating: €6,000, capped at €24,000
- Buffer tank bonus: +15% of the grant
- Solar bonus: +€1,000 flat
- Municipal top-ups: variable, stackable with the state Klimabonus
What to lock down at APS to maximise the grant?
Three items to fix before the design sketch: solar surface, buffer size and main fuel. The Klimabonus file is built on the pellet component — not on logs. Present the boiler as a pellet unit with a log back-up to simplify the paperwork.
- Plan 3–6 m² of south-facing solar collectors
- Include a buffer tank ≥ 500 L in the plant room layout from day one
- Specify an EN 303-5 Class 5 boiler compliant with EU Regulation 2015/1189 (EcoDesign)
- Document ENplus certification for the pellets
- Check municipal top-ups on the Klima-Agence simulator
Sources
Need personalised advice?
Our team supports you with selection, sizing and subsidy paperwork.