Pellet boiler in new builds: size it and integrate it from sketch stage
Actionable method for architects and project owners: boiler sizing, silo, and buffer tank to plan from sketch stage for a passive or BBC project in Luxembourg.
How many kW for a new BBC or passive project?
A BBC project (≤ 50 kWh/m².yr) typically needs 30-50 W/m², a passive house (≤ 15 kWh/m².yr) only 15-25 W/m². The classic trap is oversizing the boiler: it then runs in part-load, fouls up, and its seasonal efficiency collapses.
Quick rule: need per m² × 1.2 (DHW + backup margin) and require 30-100% modulation of nominal output as a hard specification.
- Run the load curve with the myenergy tool before freezing output in the building permit
- Lock the 30-100% modulation range into the specifications
- Single-family and collective housing: two separate sizing exercises, never a copy-paste
Silo and buffer tank: where to place them from sketch stage?
One tonne of pellets takes ~1.5 m³; a 150 m² BBC project burns 3-5 t/yr. The silo must be dry, accessible to the blower truck (≤ 30 m), and placed to keep suction within 20 m horizontal and 5-6 m vertical.
The buffer tank is not an accessory: it enables long burn cycles, cuts down on fouling, and makes thermal solar coupling straightforward.
- Silo volume: 6-8 m³ for a full season's autonomy on a 150 m² home
- Buffer tank: 20-30 L/kW minimum, 50 L/kW with thermal solar
- Plant room in the basement or cellar, never inside living space
Seasonal efficiency and maintenance: what to plan from day one
EU Regulation 2015/1189 (EcoDesign) requires a seasonal efficiency ηs ≥ 75% for any new biomass boiler. That's the regulatory floor; Tatano models reach Class 5 and go well above it.
For the building owner, operation stays light: 15 min/week for burner check, ~20-40 kg of ash per tonne of pellets, 1-2 chimney sweeps per year.
- Annual service contract: €300-450 ex-VAT, include in the running cost plan
- Specify ENplus A1 or A2 to lock moisture content under 10%
- Plan blower truck access and combustion air inlet from the sketch stage
Klimabonus and certifications: the Luxembourg framework
Klimabonus 2026 grants up to €8,000 for a single-family home replacing an old system, and €6,000/dwelling in collective housing (capped at €40,000). A buffer tank adds 15% to the grant; thermal solar adds €1,000 flat.
Municipal aid stacks on top of the state Klimabonus but varies: the Klima-Agence simulator shows, commune by commune, what really adds up. In Luxembourg, only PELLET boilers are eligible, never logs or chips.
- Confirm eligibility on Guichet.lu BEFORE ordering
- Write ENplus A1 or A2 into the specifications
- EcoDesign Class 5 is the regulatory minimum, target higher for seasonal efficiency
Sources
Need personalised advice?
Our team supports you with selection, sizing and subsidy paperwork.