ISO/TS 17595:2025

Technical
Specification
ISO/TS 17595
First edition
Solid biofuels — Characterization
2025-06
of wood chip fuels — Essential
information for producers,
suppliers and users
Biocombustibles solides — Caractérisation des combustibles à
base de plaquettes de bois — Informations essentielles pour les
producteurs, les fournisseurs et les utilisateurs
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Quality specifications for wood chips . 1
4.1 General .1
4.2 Classification of raw material .2
4.3 Normative and informative properties of graded wood chips .3
4.4 Classification of particle size classes and fines fractions.3
4.5 Specifications of graded wood chips in accordance with ISO 17225-4 .4
4.6 Typical ranges for key quality properties .5
4.7 Principles for assessing the quality of wood chip fuel .6
4.8 Procurement approaches .7
5 Standards for on-site characterisation of graded wood chips . 8
5.1 General .8
5.2 Sampling method .9
5.3 Sample preparation . 12
5.4 Bulk density .14
5.5 Moisture content . .17
5.6 Particle size distribution .18
5.7 Heavy extraneous materials .19
6 Additional standards for characterisation of graded wood chips by external laboratories .22
6.1 General . 22
6.2 Ash content . 22
6.3 Calorific value . 23
6.4 Elemental analysis: C, H, N, S, Cl and ash forming elements .24
Annex A (informative) Calculating the net calorific value based on an empirical formula .25
Annex B (informative) Model sampling plan and sampling report .26
Annex C (informative) Examples of Data Logging Tables to Record Test Results .27
Annex D (informative) Basic information included in an external laboratory test report .29
Bibliography .31

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
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This document was prepared by Technical Committee 238, Solid biofuels and pyrogenic biocarbon.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
For effective use of solid biofuels in heating and power facilities, it is crucial to assess fuel quality starting
from the planning stage through daily routine operation. It is equally critical to be familiar with the quality
specifications needed for a particular application and to determine key fuel properties using proven and
well-validated test methods.
Numerous International Standards exist to characterize various types of solid biofuels, including wood
chips, pellets, and briquettes for a variety of residential, commercial, and industrial applications. In addition
to providing detailed information on fuel specifications and classes and test methods, these International
Standards make it possible to draw up clear and unambiguous fuel supply contracts. They also support the
creation of quality assurance and certification systems.
Wood chips are among the most commonly used solid biofuels in space heating applications in commercial
and institutional buildings, district heating, light industry and greenhouses. Wood chips specifications and
test methods are described in a large number of International Standards, either as stand-alone, or as part of
International Standards addressing various types of solid biofuels.
This document is intended primarily for wood chip producers, traders, and owners and operators of energy
facilities in small to medium residential, commercial and public sectors. It is based on relevant International
Standards. The aim of this document is to provide practical guidance and examples on quality specifications
relevant to wood chips, presents guiding principles for assessing the quality of wood chip fuel and gives
common procurement approaches. Only those quality properties and their test methods that are critical
for both internal quality control purposes and smooth and efficient boiler operation are included in this
document.
Clause 4 describes general information about the quality of wood chips. Clause 5 provides guidance on test
methods for the determination of essential physical properties of wood chips. These tests can be performed
on a regular basis at the site of the wood chip fuel producer, fuel supplier or energy facility. Sampling and
sample preparation are also described in Clause 5. A calculation tool, covering the properties described in
1)
Clause 5, is available as an MS Excel document to assist users in recording, calculating and reporting test
results in a consistent manner. Clause 6 provides practical information on essential tests that are carried
out by external laboratories. Annex A gives an empirical formula to calculate energy content of wood chips.
Annex B gives an example of a sampling plan and sampling report. Annex C includes examples of data logging
tables that can be used in reporting test results. Annex D shows key information expected to be found in a
laboratory report of graded wood chips.
The sampling techniques and test methods described in this document are aligned with the methods given
in the corresponding International Standards, with minor modifications to some steps, such as sample size,
sampling frequency, number of replicates, or measurement time. This is done to make them more practical
for routine testing. As such, the methods described in this document can lead to minor differences in the
results when compared with the corresponding International Standards. These differences will not impact
the reliability of assessing changes to the properties of wood chips when measured on a relative, day-to-day
basis. Boiler operators, owners and fuel producers are encouraged to incorporate them into their regular
quality monitoring and control routines.
1) Accessible at: https://standards.iso.org/iso/ts/17595/ed-1/en

v
Technical Specification ISO/TS 17595:2025(en)
Solid biofuels — Characterization of wood chip fuels —
Essential information for producers, suppliers and users
1 Scope
This document provides guidance on the characterization of wood chips produced from raw materials, as
defined in ISO 17225-4, for the following aspects:
— quality classes and specifications;
— sampling, sample preparation and test methods for physical characteristics which can be conducted on site;
— practical information about testing to be carried out by external laboratories.
This document provides additional information about the type and frequency of testing at an energy plant
site, starting from the planning and start-up stages of a project and throughout its regular operation.
This document is applicable for assessing changes in properties on a relative basis when testing is done
routinely. This document is not applicable for demonstrating conformance with the referenced International
Standards.
2 Normative references
The following documents are referred to in the text in such a way that some or a
...