Frequently asked questions about our home energy advice tools

Our home energy advice tools estimate the energy efficiency of your home and the cost to heat and power it. The tools also estimate the carbon emissions produced as a result. 

Our tools will give you recommendations to improve your home that we think are suitable and that will save energy, money or carbon. 

Our tools calculate the energy demand of your home using information on its: 

• size 
• construction 
• age 
• heating system 
• insulation levels

Most of the calculations our tools use are the same as those used to produce an Energy Performance Certificate (EPC) but with some differences. An EPC is produced by an accredited Domestic Energy Assessor (DEA) who surveys your home.

This survey involves taking measurements and recording details about the construction of your home. Our home energy advice tools work in a similar way but rely on you entering the information instead. We also make some assumptions based on your answers. 

We, Energy Saving Trust, made the tools. We’re an independent organisation working to address the climate emergency. 

Learn more about our mission.

We can’t be held liable for any decisions or actions you may take based on the information provided. The results of these tools are to inspire and guide you on what may be possible. The results are no guarantee of the suitability or estimated savings of the recommendations given. 

Our recommendations are indicative because every home is different. Our tools need to make several assumptions about your home to give advice.

It’s important you only use the guidance from our tools as a first idea of the improvements that might be right for your home. You should consult expert installers and energy assessors before deciding to buy any new energy saving improvement. 

We calculate energy, energy bill and carbon savings on the basis that home improvements are correctly installed and maintained. The amount you may save from a home improvement will depend on several factors such as: 

• your actual heat use 
• appliance use 
• current energy bills  

Any savings you make may therefore be different from the figure given by our tools. 

The calculations used by our home energy advice tools match the methodology used to produce EPCs (called the Standard Assessment Procedure or SAP). Our calculations currently match SAP 2012 v9.94 and we’re in the process of updating to match the latest version, SAP 10.2. 

Our tools will, on average, produce a SAP score within five to six SAP points of an EPC created using SAP 2012. The accuracy of SAP ratings for your property will depend on the accuracy of your answers, and how far from typical your home is. If your home is far from typical, then it’s more likely that the assumptions used to estimate its energy use are less accurate.  

We’re not responsible for recommendations resulting from incorrect answers. Before installing measures, you should make sure it’s appropriate by speaking with accredited installers and secure any appropriate permissions where necessary. 

Our tools must make assumptions about your home to complete a full energy efficiency survey. We would need to ask you many more questions if we didn’t make assumptions.  

We ask only a select number of questions so that the tools are quick to use. Asking fewer questions also helps avoid asking technical questions only a building professional or surveyor could answer. This is important because answering a difficult question incorrectly could reduce the accuracy of the advice given by the tool.

The tools make assumptions on: 

• the size of your home 
• the materials your home is made from 
• the efficiency and other details related to your heating system 
• additional technical information about your property

The more questions you answer, the less the tools will assume. 

The assumptions made about your property are based on our analysis of UK Government housing condition survey data. Our assumptions are based on real world data to represent typical UK homes. This means the further from typical your home is, the more inaccurate our assumptions may be. 

Although our tools give results similar to an EPC, it’s not an Energy Performance Certificate as defined in the: 

• Energy Performance of Buildings (England and Wales) Regulations 2012 
• Energy Performance of Buildings (Scotland) Regulations 2008 
• Energy Performance of Buildings (Certificates and Inspections) Regulations (Northern Ireland) 2008

The report or results from the tools can’t be used in place of an EPC.  

If you need an EPC, you’ll still need to appoint an accredited Domestic Energy Assessor to produce one. For example, you’ll need an up to date EPC when you sell your home or advertise it for rent.

The tools use the answers you give to our questions and our own assumptions to estimate the energy efficiency of your home. This may lead to different results compared to a full survey of your home by a professional assessor. 

Your EPC may be out of date, especially if you have made changes to your home since the EPC was created. 

The tools use measure costs, fuel prices and carbon factors, which we review regularly. These may be more up to date than an EPC’s, especially for EPCs created a year or more ago. 

Measure costs in the tools are calculated from two parts – a fixed cost and a variable cost. The fixed cost remains a static value regardless of the details of your property. The variable cost is tied to a specific part of your property. For example, wall insulation costs vary with the area of external wall to be insulated.

A house with more external wall area will have a larger wall insulation cost than a house with less external wall area. This way, the measure costs we quote are tailored to your property.  

Each measure cost is based on the most appropriate sources available. We analyse data from: 

• funding scheme data 
• installers’ own estimates 
• prices collected from online retailers 

We review the measure costs in our tools regularly and we usually update them once a year. For some measure costs we carry out a full reassessment based on the latest available data or the most up to date methodology.

For other measures we apply inflation to our existing costs to better represent the current market situation. We use the latter when a full review isn’t possible due to no or little new information available. 

We’ve designed all measure costs to include what we consider are the typical labour and material costs.  

Labour costs typically include the cost for preparing, transporting and putting the materials in place and any necessary surveying, quality assurance or certification. 

Material costs are those of the product to be installed and include only the materials needed for a typical installation. This varies from measure to measure. 

We don’t include in our costs any additional labour or materials required to fix the state of the property to get it ready for a measure. For example, we don’t include the costs for general repairs to the material fabric or to fix damp issues. We also don’t include any remedial work required after installation to fix any snagging issues. 

All measure costs include VAT where appropriate. For many energy efficiency measures the current VAT rate is 0%. 

The costs presented in the tools are to be used as a guide. They aren’t a definitive quote for the work. Quotes from installers may be higher or lower than the costs provided by our tools. The quote you get from an installer will be influenced by the complexity of the work and the materials required, as well as geography and availability of installers in your area.

We recommend speaking with three installers, or as many as you need to feel confident that the quotes you have are competitive, before deciding on a measure. 

Measure costs on an EPC use a different source to estimate them than our tools. EPC measure costs may also be based on older cost information, especially if your EPC was created a year or more ago. We tailor the costs quoted in our tools to your property and we update our costs once a year. 

Both the tools and your EPC provide costs intended only as a guide. We recommend speaking with at least three installers to get the most accurate costs specific to your home. 

The tools calculate the energy demand of your home including the energy needed for heating, lighting and appliances. We then multiply each energy demand by a fuel price for each of the fuels used.

For heating, this will be the price of the heating fuel you’ve told us your home uses. 

We review the domestic energy market and resulting fuel prices typically paid by domestic consumers once a quarter.  

Our electricity and gas fuel prices are based on Ofgem’s energy price cap. 

We base our LPG, oil and other fuel prices on our own research into available fuel prices. 

The UK government’s Energy Price Guarantee ended in March 2023. Since then, we’ve based our electricity and mains gas prices on Ofgem’s energy price cap. Ofgem updates the energy price cap quarterly. 

We publish our current fuel prices and the date we last updated them on our website.  

The tools calculate the energy demand of your home including the energy needed for heating, lighting and appliances. We then multiply each energy demand by a carbon factor for each of the fuels used.

For heating, this will be the carbon factor of the heating fuel you’ve told us your home uses. 

We update our carbon factors once a year. 

We source our carbon factors from the UK Government’s Greenhouse Gas Conversion Factors. Businesses in the UK use these factors for carbon emission reporting. 

We give our carbon emission and carbon saving figures in kilograms of carbon dioxide equivalent per kilowatt hour of energy use (kgCO2e per kWh). 

Carbon dioxide equivalent includes the impact of greenhouse gases other than carbon dioxide. This includes greenhouse gases such as methane and nitrous oxides.

Carbon dioxide equivalent is therefore a better measure of the impact of your home’s emissions on the planet. 

We publish our current carbon factors and the date they were last updated on our website.