Our advice and data

We provide independent, evidence-based energy advice to help people make informed choices about their homes, businesses and everyday energy use.

Our advice covers:

• practical actions
• low carbon technologies
• costs
• savings
• grants and incentives
• the wider benefits of reducing energy use and carbon emissions

To support this advice, our technical, policy and consumer experts continually review the latest data sources and consumer insight from our real-world delivery.

Our team brings together specialists in:

• home energy advice
• data analysis
• policy
• retrofit
• renewable energy
• consumer communications

We use this mix of technical and practical experience to make sure our savings figures are:

• evidence-based
• useful
• realistic
• easy to understand

Our insight is informed by the advice services, research projects, tools and programmes we deliver across the UK.

This includes work with:

• households
• businesses
• local authorities
• housing providers
• installers
• governments
• other partners

We use this experience to understand:

• how energy saving measures perform in real homes and businesses
• what barriers people face
• what information they need to make confident decisions

To support advice, lots of households want to understand the likely impact of changes that they could make across their home or business, including:

• potential bill savings
• carbon savings
• up-front costs
• payback periods

We produce indicative statistics to support these decisions and to explain the assumptions behind the advice we publish.

We regularly produce and update representative costs and savings statistics. We publish information on how much money and CO₂ emissions people may be able to save at home across a range of measures, including:

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

Our 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.

Because every property is different, actual savings will vary depending on factors such as:

• property type, size and location
• existing insulation levels
• heating system
• occupancy patterns
• energy tariffs
• installation quality
• how people use their home or business after improvements are made

We want our energy saving data to represent real-life situations as accurately as possible. To do this, we gather data from a range of sources and use 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.’
• Accounting for differences between theoretical modelled performance and real-world performance, including installation quality, occupant behaviour and rebound effects where appropriate.
• 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. 
• Reviewing assumptions when policies, building regulations, technology performance, market prices or official datasets change materially.

For water savings, we use a weighted average of water and sewerage charges across water companies in England and Wales. This reflects the charging structure used in those nations and may not apply in the same way elsewhere in the UK.

For transport savings, we use average petrol and diesel prices from the previous year, alongside assumptions about average mileage, vehicle efficiency and typical journey patterns. Where Scotland-specific data is available and relevant, we use it to reflect differences in travel behaviour or fuel prices.

We review and update our typical installation costs every year, using installation cost data from the previous 12 months where available. Our sources include:

• 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 are typical costs only. Actual costs can vary widely depending 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 typical costs don’t usually include property-specific suitability assessments or remedial work, such as:

• detailed surveys
• structural alterations
• electrical upgrades
• ventilation improvement
• planning or building control requirements
• 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 different measures. They’re not intended to replace quotes based on an on-site survey. Actual costs may vary significantly, and we recommend getting at least three quotes from appropriately qualified or certified installers where possible.

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. 

We also consider whether uncertainty should be communicated in the way we present a statistic. When figures are especially sensitive to assumptions, we aim to explain the main drivers so users understand why results may differ from their own circumstances.

For fuel prices, we use different sources depending on the fuel type and geography. These may include:

• Ofgem price cap unit rates and standing charges for Great Britain, where relevant
• current prices from suppliers 
• historic prices and published market data

We cannot predict future costs with certainty. But using these sources gives the best available indication of the likely financial impact of changes to 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.

Carbon factors are expressed as kilograms of carbon dioxide equivalent per kilowatt hour (kgCO2e/kWh). They include carbon dioxide and other greenhouse gases converted into a common CO2 equivalent measure. The scope of each factor depends on the official dataset used, so figures should only be compared like for like.

Tariffs and standing charges for electricity and gas in Great Britain are calculated using an average of recent Ofgem energy price cap periods. This includes any reliable projected price caps available to us at the time. This helps smooth short-term price fluctuations while keeping our savings figures current enough to support household decision-making.

A typical update may include:

• the current price cap period
• recent previous price cap periods
• a projected future price cap, where a robust projection is available

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

Northern Ireland savings figures are based on current energy supplier tariffs for Northern Ireland, because the Ofgem price cap doesn’t apply there.

We review our savings, cost assumptions and methodology at least annually. We may update some figures more often where market conditions or official datasets change significantly. This can reduce the average expected from adding further

For example, the UK’s housing stock generally becomes more efficient over time as new homes are built to higher standards and existing homes are improved. This can reduce the average savings expected from adding further measures.

Costs and savings for renewable technologies can also change quickly as incentives, supply chains, installation capacity and market demand change. We therefore review assumptions for some technologies more frequently 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.

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 public-facing statistics for detailed financial modelling, policy appraisal or investment analysis without further advice.

We have different statistics and methodologies for more detailed modelling. We can provide a consultancy support service for businesses or organisations that need more detailed analysis.