Overview
SIST EN ISO 17225-5:2026 specifies the fuel quality classes and requirements for graded firewood used as a solid biofuel. Developed by the Slovenian Institute for Standardization (SIST) and aligned with ISO and CEN standards, this document establishes clear criteria for the classification and specification of firewood intended for residential, small commercial, and public building applications.
The standard applies exclusively to firewood produced from:
- Whole trees without roots
- Stemwood
- Logging residues (thick branches, tops, etc.)
- Chemically untreated by-products and residues from the wood processing industry
By defining strict guidelines for fuel specifications, SIST EN ISO 17225-5:2026 ensures reliable fuel quality, supports sustainability, and enhances the efficient use of solid biofuels.
Key Topics
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Fuel Quality Classes
The standard divides graded firewood into three main quality classes (A1, A2, B), based on the origin of raw materials, moisture content, dimensions, and presence of decay or mould.
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Specification Parameters
- Wood species: Must be stated (e.g., spruce, beech).
- Diameter: Defined classes for main and oversized fractions.
- Length: Typical lengths range from 20 cm to 100 cm.
- Moisture content: Minimum and maximum thresholds set for each class.
- Volume or weight: Sales units such as stacked or loose cubic metres, or kilograms must be specified.
- Quality declaration: Must be indicated by producer or supplier.
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Moisture Content and Energy Density
The standard provides conversion tables and formulas for calculating moisture on both wet and dry bases, as well as methods for estimating energy density (kWh/m³ or MJ/kg).
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Sampling and Analysis Methods
Reference is made to established ISO procedures for sampling, sample preparation, and moisture determination, ensuring robust and reproducible results.
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Sustainability and Safety
Use of untreated and uncontaminated wood is emphasized, with recommendations for analysis if contamination is suspected.
Applications
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Residential Heating
The standard is indispensable for users of wood-burning stoves, fireplaces, room heaters, cookers, and boilers, ensuring appliances operate safely and efficiently.
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Small Commercial and Public Buildings
Administrators and service providers in small-scale heat generation benefit from standardized, reliable firewood quality, supporting operational efficiency and regulatory compliance.
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Producers and Suppliers
Producers, suppliers, and retailers of firewood use the classification and specification criteria to ensure transparency with buyers, facilitate efficient trading, and meet market and regulatory requirements.
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Equipment Manufacturers
Manufacturers of combustion devices can optimize equipment for specific firewood classes, guaranteeing performance and customer satisfaction.
Related Standards
- ISO 17225-1:2021: General requirements for solid biofuels - essential baseline for all fuel classes.
- ISO 18134-1 & ISO 18134-2: Methods for determination of moisture content in solid biofuels.
- EN 13556: Nomenclature for timber species used in Europe.
- EN 13229, EN 12815, EN 12809: European standards for testing stoves, cookers, and boilers.
- ISO 18125: Determination of calorific value for solid biofuels.
By using SIST EN ISO 17225-5:2026, stakeholders support best practices in renewable energy, contribute to emissions reduction, and promote the responsible utilization of solid biofuels throughout Europe and internationally. This standard is crucial for anyone engaged in the production, supply, regulation, or consumption of firewood as a sustainable energy source.