Our data

One of our ambitions is to support UK-wide access to comprehensive, independent, and tailored energy advice for homes and businesses. 

To support this, we regularly produce and update representative costs and savings statistics. We publish information on how much money and CO₂ emissions you can save in the home. This covers a range of measures including: 

• insulating your home
• installing solar panels 
• buying the most efficient appliances 

Our energy saving data calculations give an initial idea of potential savings. They’re not intended to replace costs and savings based on surveys or specific data about a particular home. 

We want our energy saving data to represent real-life situations as accurately as possible. We gather data from diverse sources, including national surveys and government reports, and use various statistical methods to draw meaningful conclusions. 

• Looking at housing stock data from sources including statistics from the Department for Energy Security and Net Zero (DESNZ). 
• Calculating how much insulation is installed and assessing the average efficiency of boilers across the UK. 
• Using U-values from the Standard Assessment Procedure (SAP), and government ‘in-use factors’ to account for the difference between modelled savings and in-situ savings.  
• Accounting for the ‘heat replacement effect’. 
• Updating the carbon factors we use each year with the latest published data from DESNZ.  
• Cross checking and validating our existing models, making changes where necessary. 

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 savings, we use average petrol and diesel prices from the previous year for the UK and Scotland and use assumptions related to the average mileage. 

We review and update our typical installation costs every year. We do this by using installation costs data relating to the last 12 months, depending on availability. The data comes from several sources such as: 

• national energy efficiency schemes 
• installers 
• retailers 
• professional industry organisations 

We analyse these sources and adjust according to inflation, location, and date. 

The costs on our website illustrate a typical cost only. Costs vary widely and depend on factors such as: 

• property size and construction 
• having less choice of installers in an area 
• having higher living costs in cities like London 

Our costs don’t typically represent any suitability assessment or remedial work such as surveys, structural alterations or redecoration. 

We calculate costs for different house types using fixed dimensions from the Building Research Establishment (BRE). Where no house type is mentioned, we use the average or median cost to represent the most common cost. 

If you calculate payback periods using our costs, be aware that our costs don’t include any replacement parts or maintenance. Using a simple payback methodology (installation cost divided by annual savings) doesn’t consider: 

• discount rates 
• future energy prices 
• inflation 
• the lifetime of the installation 

Therefore, this kind of calculation should be used with caution. 

Our numbers provide indicative costs for installing various measures to give you an idea what to expect. They are in no way intended to replace quotes based on an on-site survey with specific data and actual costs may vary significantly. We always recommend you get at least three quotes. 

As time goes on, more criteria can be measured and factored in to help improve the quality of our data. For example, our heating savings are modelled alongside improvements to the Standard Assessment Procedure. This is the methodology used to assess the energy efficiency of homes. We also apply statistical methods to help inform how much confidence we have in our assumptions. 

Field trials and other in-situ monitoring help us to validate our calculations. We’re always looking for high quality data to best represent the current situation for homes and businesses. 

For fuel prices, we use a combination of: 

• the UK Government’s predicted energy prices for the coming year 
• current prices from suppliers 
• historic prices  

While we can’t predict future costs with certainty, this gives the best indication of the likely financial impact of any changes you might make to your energy use. 

Our energy saving data calculations assume the following average fuel prices and carbon factors for Great Britain (GB) and Northern Ireland (NI) homes. 

Tariffs and standing charges for electricity and gas in GB are calculated using an average of the four most recent energy price caps, including any projected price caps available to us at the time.

Typically this will include the:

• June tariff
• two previous tariffs
• projected tariff for September

Projected tariffs are provided by Cornwall Insight who’ve given us permission to use their figures for this purpose.

NI savings figures are based on Northern Ireland’s current energy supplier tariffs. 

We review all our savings and costs assumptions and methodology at least annually. For example, as a trend, the UK’s housing stock average becomes more efficient year-on-year, as new-built homes are better insulated, and some existing homes are improved. We also factor this into our savings, acknowledging that you get fewer savings per each measure as you install more measures. 

Renewables can also frequently change, where incentives change and the up-front costs react quickly to market demand. In the case of solar panels in particular, the system costs fell quite dramatically over several years but have started to rise again. We review some assumptions with a higher frequency than others. 

Gas and electricity prices have changed quickly in the last few years, and carbon factors change from year to year, sometimes quite substantially. These factors influence how much money and CO₂ emissions you can expect to save from installing energy efficiency measures or low-carbon technologies.

The frequency of our updates considers all the above, and we release an update when these changes are likely to influence the decision you may make about your home.   

If you want to use our statistics, please clearly source: 

• Energy Saving Trust, citing the relevant webpage
• the date the information was last updated (this is displayed on the relevant webpage) 
• the energy prices the data is based on, where applicable 

We don’t recommend using our statistics for any financial modelling or analysis. We have different statistics and methodologies for this purpose. We can provide a consultancy service for businesses or anyone who needs more support.