Wood Fuel Standards Wood Fuel Testing

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Wood Fuel Standards

In order for the wood to be used to produce heat efficiently in an appliance such as a boiler it has to meet specific quality standards. Standards are required to describe biomass fuels, and testing gives confirmation of adherence to standards. In order to ensure quality, it is necessary to regularly sample and test fuel to ensure that it meets customer expectations, appliance requirements and product description.

There have been several standards used in the UK biomass industry for the provision of wood fuel for use in RHI boilers, they are:

  1. Önorm (M7 133)
  2. EN 14961
  3. ISO 17225


The Önorm standard for woodchip (M7 133) was published by the Austrian Standards Institute as a national standard, and was primarily used by a large number of biomass boiler manufacturers based in Austria. Austrian boilers where then shipped to, and installed in, the UK and the Önorm standard was adopted by UK fuel suppliers when supplying chip to these boilers. The Önorm standard had other influences also, with many boiler and feed system designs for current boilers dating back a number of years, originally being designed with Önorm in mind. 

Particle size classes under Önorm M7 133 were G30 for finer grade chip and G50 for a larger size of chip.

In 2011 the Önorm M7 133 standard was withdrawn, and replaced by EN 14961.  All EU member states were required to adopt EN 14961 as their princile standard for Solid Biomass. 

EN 14961

EN 14961 was a European Standard which was originally ratified in 2010 to replace all national standards within EU member states for solid biomass for non-industrial use. The EN standards covered pellets, firewood, briquettes and woodchip in sub-sets 1-6 of the standard. The EN standard also gave a more rigorous size specification than the Önorm standard, specifying a number of different size classes for wood chip, along with the relevant normative (required) and informative (optional) elements of the described fuel. 

EN 14961 also gave some interoperability with the Önorm standard in the size classes, as G30 and P16B, and G50 and P45 were virtually the same, meaning that a boiler requiring chip to the Önorm standard could utilise fuel produced to the EN standard.

EN 14961 was officially withdrawn at the end of May 2015. However, as most boilers that are currently operating under the RHI scheme have been commissioned to accept fuel based on EN 14961, we are still able to test to this standard.

ISO 17225

This standard was launched in Europe in 2014, and broadens the scope of the classification of biomass fuel, introducing a number of new particle size classifications, which in broad terms are less stringent than EN 14961.

The testing methods used for ISO 17225 do not vary greatly from those used to obtain results for EN14961; the difference between the two standards is more distinguishable in how the results of the tests are presented.

This is a very new standard, only being published in the UK at the end of May 2015 as a direct replacement for the EN standards. We are currently awaiting feedback from the Government as to how the new standard is going to fit into the RHI scheme.