Passive or BBC new build in Luxembourg: how to size a pellet boiler from day one?
Heating load, silo, buffer tank and Klimabonus 2026: what must be integrated from APS for a passive or BBC new build in Luxembourg.
What boiler power for a passive or BBC new build in Luxembourg?
Even in a well-insulated passive house, the peak heating load rarely falls below 4 kW during the coldest week: wind exposure, air leakage and thermal bridges quickly erode the safety margin.
For a typical 180 to 220 m² passive home in Luxembourg, plan 3 to 6 kW for space heating plus 2 to 3 kW for domestic hot water. Oversizing is the most common mistake — it kills both efficiency and emissions performance.
- BBC / low-energy: roughly 25 to 50 W/m² depending on compactness and ventilation
- Passive (15 kWh/m²/yr): 3 to 6 kW for 200 m² including DHW
- Specify a modulating burner to keep the load above 30 %
- Make EcoDesign EU 2015/1189 and EN 303-5 Class 5 mandatory in the brief
How to integrate the silo and buffer tank at the design stage?
A pellet boiler is not a kitchen appliance: its logistics (silo, suction line, buffer tank, maintenance access) must be designed with the very first architectural plan — not three weeks before delivery on site.
What isn't locked in at APS becomes a costly construction surprise: missing 30 cm for the feed pipe, silo too close to a fire-rated wall, no truck access for the delivery hose.
- 3 to 6 m³ silo per home ≈ 2 t of pellets = one full heating season without refilling
- Vacuum suction up to 15 m, or an auger for longer runs
- Buffer tank 500–800 L single-family, ≥ 1 000 L small collective
- Plan forced ventilation, a fire-rated hatch and an inspection port (EN 303-5)
What seasonal efficiency and maintenance should you expect?
A modern biomass boiler certified EcoDesign (EU 2015/1189) and EN 303-5 Class 5 delivers 85 to 92 % seasonal efficiency — on par with a modern gas boiler, with a CO₂-neutral fuel.
The real lever is fuel quality: ENplus pellets (≤ 8 % moisture, ≤ 0.5 % fines). Anything else clogs the heat exchanger and drags the efficiency down — much like cheap oil in a precision engine.
- Ash removal: 1 to 3 times per month depending on the load
- Annual service of the combustion chamber and temperature sensors
- Buffer tank: safety valve every 2 years, circulator inspection every 5 years
- Refuse any non-conforming delivery: the discount is paid back in lost efficiency
How much can you actually claim in Luxembourg in 2026?
Only pellet boilers qualify for the Klimabonus 2026 — logs and wood chips are explicitly excluded. A common filing error that can invalidate the application.
The Klimabonus 2026 stacks with municipal aids: amounts vary widely (from zero to several hundred euros) and most are fully cumulative with the national grant.
- Up to €8,000 per single-family home (€4,000 without replacing an old system)
- €6,000 per unit in collective housing (cap €40,000)
- €6,000 in district heating (cap €24,000)
- Bonus: +15 % with a buffer tank, +€1,000 flat with solar thermal
- Municipal aid: run the simulator at aides.klima-agence.lu before finalising the APS
Sources
Need personalised advice?
Our team supports you with selection, sizing and subsidy paperwork.