Sizing a Pellet Boiler for a New BBC/Passive Build in Luxembourg: The Method from Concept Design
Expert method to calculate pellet boiler output for passive or BBC homes. Avoid oversizing, meet EcoDesign, secure Klimabonus 2026 incentives.
Why sizing changes for BBC/Passive builds
In high-performance homes, heat losses are low. An oversized boiler short-cycles, wears the burner and falls out of its optimal efficiency range.
The required output sits in a low range for a villa, well below legacy standards.
How to calculate the true required output?
The design heat load is determined by dynamic simulation (PHPP, Th-BCE or equivalent) room by room, including solar and internal gains.
Retain the load at the base point without arbitrary safety factors.
- Minimum modulation selected to cover part load.
- Nominal output selected as close as possible to the calculated peak load.
Regulatory and incentive requirements that drive the choice
Regulation (EU) 2015/1189 mandates seasonal efficiency ≥ 75 % (≤ 20 kW) and PM ≤ 40 mg/m³ for auto-feed.
Klimabonus 2026 adds: dust ≤ 8 mg/m³, NOx ≤ 200 mg/m³, generation efficiency ≥ 90 %, automatic ignition and feed.
- ENplus A1 pellets mandatory (ash ≤ 0.7 %, moisture ≤ 10 %).
- Grant up to 8 000 € single family, +15 % with 30 l/kW buffer, +1 000 € solar thermal.
Hydraulic integration and next step
The buffer tank (Pufferspäicher) decouples generation from emission, absorbs start-up peaks and ensures minimum burn time.
Plan the plant room (Heizungsraum) with silo access, tight flue and space for the buffer from sketch stage.
- Request the Tatano energy study: sizing, hydraulic scheme, incentive estimate.
Sources
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