Overview
EN ISO 17225-4:2021 - Solid biofuels: Graded wood chips defines fuel quality classes and specifications for graded wood chips used as solid biofuel. Published by CEN and identical to ISO 17225-4:2021, this part of the ISO 17225 series covers wood chips produced with sharp tools from the following raw materials:
- forest, plantation and other virgin wood;
- by‑products and residues from the wood processing industry;
- chemically untreated used wood.
The standard explicitly excludes hog fuel (produced with blunt tools) and gives guidance to support trading, equipment compatibility and regulatory reporting for residential, commercial and small/medium industrial heating applications.
Key topics and technical requirements
- Fuel quality classes - Defines property classes (e.g., A1, A2, B1, B2) that group fuels by origin and typical quality (A classes for virgin/untreated residues; B classes extend to more diverse or partly treated sources).
- Particle size and grading - Updated particle size distribution classification to ensure compatibility with conversion equipment. The standard references ISO 17827‑1 (oscillating screen method) for particle sizing.
- Moisture, ash and chemical properties - Moisture and ash content classes updated in this edition; chemical contaminants (e.g., heavy metals, halogenated organics) are addressed when raw material suspicion exists. Relevant test methods are cited (ISO 18134‑2 for moisture, ISO 18122/18135 for ash and sampling).
- Sampling and analysis - Sampling and sample preparation must follow ISO 18135/ISO 21945 and ISO 14780 to ensure representative test results.
- Bulk density guidance - Informative Annex A provides general guidelines for bulk density of graded wood chips (loose volume).
- Traceability and declaration - Requirements for declaring raw material origin (especially for chemically treated sources) and for performing additional analyses when contamination is suspected.
Applications and users
EN ISO 17225-4:2021 is intended for:
- Fuel suppliers and traders specifying and selling graded wood chips.
- Boiler and gasifier manufacturers checking fuel compatibility and designing feed systems.
- Facility managers and heating contractors selecting appropriate fuel for residential, commercial and public building installations.
- Testing laboratories and certification bodies performing sampling and analysis.
- Regulators and procurement teams requiring standardized fuel specifications for permits and public procurement.
Typical application scales noted in the standard range from below 100 kW (residential) up to several MW (small/medium district heating and commercial systems).
Related standards
Keywords: EN ISO 17225-4:2021, graded wood chips, solid biofuels, fuel specifications, wood chip quality classes, moisture content, particle size, bulk density, ash content, sampling and analysis.
