First we look at the state of the housing stock – with data sources such as the English Housing Survey and statistics available from the Department of Business, Energy and Industrial Strategy (BEIS). We can then work out how much insulation is installed and assess the average efficiency of boilers across the UK. We use U-vales from the Standard Assessment Procedure, or SAP, and government in-use factors to account for the difference between modelled savings and in-situ savings. We also account for the heat replacement effect.
Then we review domestic energy prices based on data that we purchase. We also update the carbon factors we use each year with the latest published data from the Department for Business, Energy and Industrial Strategy (BEIS). From there, it’s about cross-checking and validating our existing models, and making changes where necessary.
When it comes to our water savings, we assume all bill savings from water meters based on a weighted average of water and sewerage charges for all companies in England and Wales. For transport related savings, we use average petrol and diesel prices from the previous year for the UK and Scotland and make assumptions related to the average mileage for each region.