Free: Heating Degrees Days Data

At this time of year, the outside temperatures start to drop to below freezing and attention turns to getting the best performance from your building’s heating system.

For organisations seeking to understand their building’s energy performance and forecast your energy usage with greater confidence, the use of Heating Degree Day (HDD) is a valuable metric.

A Heating Degree Day is a measurement designed to reflect the demand for energy needed to heat a building. It is derived from measurements of outside air temperature. The heating requirements for a given structure at a specific location are considered to be directly proportional to the number of HDD at that location. A similar measurement, cooling degree day (CDD), reflects the amount of energy used to cool a home or business.

So, HDD can provide a simple metric for quantifying the amount of heating, that buildings in a particular location need over a certain period (e.g. a particular month or year). In conjunction with the average U-value for a building, they provide a means of roughly estimating the amount of energy required to heat the building over that period.

There is an opportunity to integrate the HDD data with your half hourly energy data to improve the analysis of a building’s energy performance and be able to forecast your energy usage with greater confidence.

A useful free web-based resource is available to download daily half hourly temperature and daily degree day data for over 80 UK zones (e.g South East) and even refine the data to local cities (e.g. Brighton and Hove, Eastbourne or another five other cities in the South East zone) within the zone.

Main PageHDD Data PageTo download the Heating Degree Day (HDD) data, go to and click on the three thermometers graphic in the top right hand corner of the website.

The next web-page allows for the selection of the UK zone and nearby city, the type of report, the reporting period & whether you want to view the report in your web browser or have the report sent by e-mail.

For further information on the use of monthly degree days in energy performance analysis and its strengths and weaknesses, there is an excellent technical paper: Degree-days: Theory and Application written by Professor Tony Day and published by Chartered Institution of Building Services Engineers (CIBSE) available at

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