New build passive house in Luxembourg: how to size a pellet boiler at the design stage
Passive house or BBC new build in Luxembourg: size the pellet boiler, silo and buffer tank at APS to maximise your Klimabonus 2026 eligibility.
What boiler size for a passive or near-zero project?
A passive house uses under 15 kWh/m²/year; an NZEB label ranges 15-50. For 150 m², the annual heating demand often drops below 2,500 kWh. A 6-10 kW boiler is enough — oversizing causes short cycling and erodes seasonal efficiency.
Always target a power rating 20 to 30% below the design peak. A buffer tank smooths demand and unlocks compact boiler models, compliant with EN 303-5 Class 5 and EU Regulation 2015/1189 (EcoDesign).
- 100 m² passive → 4-7 kW
- 150 m² passive → 6-10 kW
- 200 m² NZEB → 8-12 kW
- Always pair with a buffer tank of at least 500 L
How to fit the silo and buffer tank at concept stage?
The pellet silo is sized for the autonomy you want. Plan on roughly 650 kg/m³ bulk density; a 150 m² home burning 3 tonnes per winter needs 4-5 m³ of usable volume. Reserve truck access for pneumatic delivery from day one.
The buffer tank is more than a hydraulic volume: it triggers the +15% Klimabonus 2026 bonus. Reserve 1-1.5 m² of floor area next to the plant room, with all hydraulic connections pre-planned.
- Silo access: Ø 100 mm fill port minimum, dry technical shaft
- Silo-boiler distance ≤ 15 m to preserve suction efficiency
- Dry, frost-free, ventilated room, away from living spaces
What seasonal efficiency and maintenance should you anticipate?
A modern pellet boiler reaches 85 to 95% seasonal efficiency. EU Regulation 2015/1189 sets minimum thresholds by class — specify Class 5 in your brief. Plan for ash disposal and chimney sweeping once or twice a year.
Routine maintenance takes about 30 minutes per month: cleaning the burner pot, emptying the ash box, checking the silo. An annual service contract preserves warranty and regulatory compliance — include this line item in your operating cost forecast from APS onwards.
- Target seasonal efficiency: > 90%
- Chimney sweep: 1-2 times/year
- Pellet storage: require ENplus A1 certification
- Service contract: budget from APS stage
Pellets vs wood chips for a new multi-family project?
In Luxembourg, Klimabonus 2026 funds pellet boilers only — not chips, not logs. For a new multi-family project, this almost always steers the choice toward pellets: standardised logistics, ENplus certification, dry fuel all year.
Wood chips stay interesting for large outputs (>100 kW) tied to a heating network, but they need a bigger plant room, a 20-40 m³ silo and a dedicated supply contract. Compare both options at APS using the Klima-Agence aid simulator and check municipal top-ups, which vary from one commune to another.
- Pellets: Klimabonus 2026 eligible, ENplus certified, bulk or bag delivery
- Wood chips: not Klimabonus eligible, reserve for projects >100 kW
- Municipal aids: vary by commune, can be stacked with Klimabonus
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