# Regulation (EU) 2016/426 of the European Parliament and of the Council of 9 March 2016 on appliances burning gaseous fuels and repealing Directive 2009/142/EC (Text with EEA relevance), Division 2: The reference conditions for Wobbe index and gross calorific value shall be the following:

Extent: E+W+S+N.I.

(a)
combustion reference temperature:
15 °C;
(b)
volume measurement reference temperature:
15 °C;
(c)
volume measurement reference pressure:
1 013,25 mbar.

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Source: https://www.legislation.gov.uk/eur/2016/426/annex/II/division/2 (the official version)
Page: https://openlegislation.uk/eu-regulation-2016-426/annex-II/division-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.