Pellets vs wood chips for a new collective building in Luxembourg: what the architect must decide at APS
Pellets vs wood chips for new multi-family housing in Luxembourg: boiler room, silo sizing, Klimabonus 2026. What architects must fix at sketch design.
Why the pellet vs wood chip choice is decided at sketch design
On a new collective housing project, the pellet vs wood chip decision goes beyond fuel: it dictates silo volume, delivery method, noise on intake, and — in Luxembourg — eligibility for state aid.
Architects who fix these constraints at the APS stage avoid costly rework in the design development phase and secure the Klimabonus file from day one.
Pellets or wood chips: what is the practical difference for the boiler room?
ENplus-certified pellets weigh ~650 kg/m³ and are blown in via a DN 100 duct from a tanker truck. Wood chips weigh ~250 kg/m³ and require a reinforced silo floor plus an auger or rake extraction.
This mass and logistics gap translates directly into silo volume and annual delivery frequency.
- Usable silo volume for 10 kW over one heating season: ~5 m³ pellets, ~15 m³ wood chips.
- Delivery cadence: 1–2 times/year for pellets; 3–5 times/year for wood chips.
- EN 303-5 Class 5 is required for both, but a particle filter is more critical on wood chip installations.
- Klimabonus 2026: only pellet boilers are subsidised in Luxembourg.
How do you size the silo and buffer tank from the design development stage?
In a new BBC or passive building, boiler output typically ranges from 8 to 25 kW depending on dwelling count. Correct sizing avoids short cycling, which lowers seasonal efficiency and accelerates fouling.
Three details to lock in on the drawings now — to prevent late redesigns on site.
- Silo: 1.5–2 m³ per dwelling (one-season autonomy target); inspection hatch compliant with local fire codes.
- Buffer tank: 20–30 L per kW of boiler output; combine with solar thermal for an extra €1,000 Klimabonus bonus.
- Delivery duct: DN 100, max 8–12 m, two 45° elbows instead of 90°, outdoor inlet within 30 m of the boiler.
- Boiler room: high/low ventilation (50 cm² per kW), sealed floor, ABC dry-powder extinguisher.
Klimabonus 2026 and municipal top-ups: the numbers in practice
The 2026 state Klimabonus for a pellet boiler in a collective building pays up to €6,000 per dwelling, capped at €40,000 per project. The buffer tank bonus adds +15%, and coupling the boiler with solar thermal grants an extra €1,000 flat fee.
Municipal top-ups vary widely by commune and stack with the Klimabonus — check the official aid simulator before locking the financial plan.
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