New-build passive house in Luxembourg: how to size a pellet boiler from the APS
Silo sizing, buffer tank, Klimabonus 2026: a practical guide for architects and project owners designing an energy-efficient new build.
What kW for which home? The right-sizing rule
A passive or BBC new build in Luxembourg uses very little heating energy, but an oversized boiler cycles too often and loses 10–15 % of seasonal efficiency. The right reflex is to calculate the design heat load with a regulatory tool such as REG-Lux — not to rely on a rule of thumb.
- BBC single-family home (~120 m²): 4–6 kW is usually enough.
- Passive house (~150 m²): 5–8 kW, depending on ventilation and solar gains.
- Multi-unit BBC building: 3–5 kW per dwelling, validated by a thermal study.
- Always include domestic hot water demand in the calculation.
Pellet silo and buffer tank: integrate them from the APS
The silo and buffer tank drive the layout of the boiler room. Position them on the plan during the APS stage or the room quickly becomes unworkable. Also plan truck access for deliveries (flex hose or auger).
- 4–6 t silo = 6–9 m³ of usable volume (≈ 1 year of autonomy).
- Fabric silo: flexible option, fits most existing cellars.
- 500–1 000 L buffer tank: fewer cycles, longer boiler life.
- Ø 100 mm fill pipe, accessible from the street.
Maintenance, EcoDesign and service access: design for it now
EU Regulation 2015/1189 (EcoDesign) sets minimum efficiency and emission thresholds. The architect must provide ash removal, high/low ventilation and clear service access from day one.
- EN 303-5 Class 5: required for European compliance.
- ENplus-certified pellets: consistent quality, less ash.
- Boiler room: 200 cm² low vent + 200 cm² high vent.
- Plan water supply and a drain for ash handling.
Klimabonus 2026 and municipal grants: the financial framework
Klimabonus 2026 only supports pellet boilers — never log or wood-chip systems. The amounts are capped but bonuses stack, which can cover a meaningful share of the investment. Municipal grants top it up and vary by commune.
- Single-family home: up to €8 000 (€4 000 without replacing an old system).
- Multi-unit building: €6 000 per dwelling, capped at €40 000.
- District heating: €6 000, capped at €24 000.
- +15 % with a buffer tank, +€1 000 with solar thermal.
- Stackable with municipal grants — check the klima-agence simulator.
Sources
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