# Commission Delegated Regulation (EU) 2015/2402 of 12 October 2015 reviewing harmonised efficiency reference values for separate production of electricity and heat in application of Directive 2012/27/EU of the European Parliament and of the Council and repealing Commission Implementing Decision 2011/877/EU, Division (c): Method for establishing climate zones:

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

The borders of each climate zone will be constituted by isotherms (in full degrees Celsius) of the annual average ambient temperature which differ at least 4 °C. The temperature difference between the average annual ambient temperatures applied in adjacent climate zones will be at least 4 °C.
A first climate zone between the isotherms of 9 °C and 13 °C (4 °C difference) with an average annual ambient temperature of 11 °C, and
A second climate zone between the isotherms of 5 °C and 9 °C with an average annual ambient temperature of 7 °C.

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Source: https://www.legislation.gov.uk/eur/2015/2402/annex/III/division/1/division/c (the official version)
Page: https://openlegislation.uk/eu-regulation-2015-2402/annex-III/division-1/division-c
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.