Home Energy Efficiency Tool: what it does and how to use it

The Home Energy Efficiency Tool is a digital tool that uses a market leading calculation engine to give tailored energy efficiency advice¹. It takes an address and a short set of details about the building, then returns a personalised action plan: what to do, in what order, what it is likely to cost, what it could save on bills and carbon, and an indicative energy rating for the home.

It is built and run by the Energy Saving Trust, the grant-awarding body and advice organisation that also supplies the calculation engine behind several council, retailer and utility services². The householder-facing versions are free. Home Energy Scotland, for example, offers free advice on improving the energy efficiency of your home³, and the tools that sit inside council schemes are provided at no cost to the resident.

The tool is a planning instrument, not a certificate. It does not lodge an Energy Performance Certificate, and it does not replace an assessment by an accredited assessor. What it does is turn the data already held about a property into a ranked list of measures with numbers attached, which is the point at which most households move from wondering where to start to booking work.

What the Home Energy Efficiency Tool does

The tool exists to answer a question most households cannot answer from a bill: how efficient is this home, and which changes would actually reduce its energy use⁷. It does that by combining what is already recorded about a property with what the householder reports, then running the combination through a calculation engine that produces measure-by-measure advice.

The output is not a single number. HomePlus, one of the services built on the same engine, gives customers a personalised report and an action plan to improve energy efficiency, and it also provides potential carbon savings¹. Customers can discover optimum energy saving solutions to suit their budget and understand the potential bill savings to be made from implementing home upgrades¹. That combination, a ranked list plus a cost and a saving against each item, is what separates the tool from a general advice page.

The engine behind it is used at scale. City Plumbing Supplies uses Energy Saving Trust's digital Home Energy Improvement Tool to provide its customers with energy efficiency advice across 360 City Plumbing branch locations and online², and the same organisation developed a bespoke Energy Saving Tool for Yorkshire Building Society². B&Q's Energy Saving Service was built as a bespoke product using the Home Energy Efficiency Tool and Dynamic Engine technology⁴. For a householder, the practical consequence is that the same underlying calculation appears under several different front doors, and the advice should be consistent whichever one is used.

What the tool does for independence is modest but real. It reduces reliance on a single installer's opinion about what a house needs, because the recommendation comes from a calculation rather than a sales visit. It does not remove the dependence on a supplier, a grid connection or a gas network, and it does not carry out any work. It is a map, not a vehicle.

Who makes it: Energy Saving Trust

The Energy Saving Trust is the organisation behind the tool. It is described in official guidance as a grant-awarding body⁸, and it also provides advice on energy at home and a guide to green renovation to help households put energy efficiency first room by room³. That dual role, grant administration and public advice, is why its calculator carries weight with councils and with the services that license it.

The Trust's tools are white-labelled into other organisations' services rather than only offered directly. HomePlus states that the Energy Saving Trust's Home Energy Efficiency Tool is now an integral part of its HomePlus Digital Home Report¹. City Plumbing Supplies is using Energy Saving Trust's digital Home Energy Improvement Tool to provide its customers with energy efficiency advice². The Trust has also developed a bespoke Energy Saving Tool for Yorkshire Building Society².

This matters for how a householder should read the output. The advice is impartial in the sense that the Trust does not sell installations, but the front door through which it is reached may be a retailer, a lender or a council with its own onward offer. The calculation is the Trust's; the surrounding service is not.

The Trust also publishes separate calculators for specific measures. Its solar panel calculator uses the size, insulation and energy performance certificate rating from your home or similar homes⁵, and it states that if it cannot find your home in its database it can still provide potential savings, but they will not be specific to your home⁵. That is the clearest published statement of how the family of tools behaves when the data is thin.

What you need to enter: your address and home details

The starting point is the address. Which?'s home energy planning service asks users to register with a name and email, then enter a postcode and select the address⁹. The address is not incidental: it is the key that unlocks the records already held about the property.

Those records are extensive. The Energy Performance of Buildings Regulations set out the data items that may be used to produce a certificate for a residential building, including the address and postcode, the energy rating and potential energy rating, building type and built form, floor area, glazing, extensions, fuel type, heating systems and controls, insulation, lighting, ventilation, solar water heating, construction age band, tenure type and air permeability¹⁰. A certificate must also carry the address of the building⁸.

In practice the tool gathers a home's address, the building's age, construction and Energy Performance Certificate rating, along with a customer's current energy use⁴. The householder supplies the parts that are not on a register: how the home is heated, how it is used, and what the budget is.

The National Energy Efficiency Data-Framework shows what sits behind this kind of analysis at national level: property level data including gas and electricity consumption from 2005 to 2022, property characteristics and energy efficiency measure installations¹¹. The same framework is used to assess the impact of installing home efficiency measures such as loft insulation on household energy consumption¹². A householder is not seeing that dataset, but the tool's estimates rest on the same kind of evidence.

What the plan tells you: savings, EPC rating, costs and CO2

The plan's core output is a set of measures with money and carbon attached. Homewise tells residents the cost of any recommended energy efficiency improvements and any potential carbon and energy bill savings¹³. Which?'s service shows home data, improvement options, ballpark costs, bill savings, grant checks, ways to pay and trusted installers⁹. HomePlus provides potential carbon savings alongside the bill figures¹.

The rating element is indicative. An EPC provides an assessment of a home's energy efficiency¹⁴, and each EPC comes with a report setting out the cost effective measures that homeowners or businesses can take to improve energy efficiency and energy rating, such as low energy bulbs or upgrading insulation¹⁵. The tool mirrors that structure without producing the lodged certificate.

The rating system itself is in flux, which affects how a plan should be read. The Scottish Government has consulted on reforming the current metrics to provide more holistic information about the efficiency of a home that is relevant to owners and occupiers¹⁶, and its stated limitation is that the current metrics do not accurately reflect the fabric efficiency of a home nor do they support the transition to net zero¹⁶. A new set of ratings has been proposed: a Heat Retention Rating reflecting fabric energy efficiency, a Heating System Rating covering type, emissions and efficiency, and an Energy Cost Rating. Those new certificates and ratings are intended to help monitor progress in the heat decarbonisation target and to underpin minimum energy efficiency standards¹⁷.

For context on what the numbers mean, a home rated EPC C or above is generally regarded as having an adequate level of energy efficiency¹⁸. Official statistics also break down delivery at national level, including further analysis and geographical breakdowns of ECO measures, ECO delivery costs, estimated carbon and energy savings from measures installed and the supply chain¹⁹.

Setting a goal and a budget to shape your plan

The plan is shaped by two inputs the householder controls: the target and the money available. Setting a target is a separate decision from running the tool, and the site's guide to setting a target for your home covers the choice between an EPC band, a bill reduction and low-carbon heat.

Budget is the constraint that reorders the list. HomePlus is explicit that customers can discover optimum energy saving solutions to suit their budget and understand the potential bill savings to be made from implementing home upgrades¹. Homewise produces a tailored retrofit action plan from its property tool, with a personalised home energy action plan, an indicative EPC rating and a breakdown of the cost for any work and potential savings²⁰.

Where the budget is very small, the tool's value is in sequencing rather than in the size of the measures. The site's guide to starting on a small budget deals with that case directly, and quick wins and no-cost measures covers the items that need no capital at all.

Grant funding is the third input, and it varies by nation. The Northern Ireland Housing Executive's home energy saving tool states plainly that there may be energy grant help to allow you to make these changes²¹, and it can be used to create an action plan to make your home more energy efficient²¹. In Wales, the Nest scheme's customer charter requires households to give correct information at the right time²². In Scotland, Home Energy Scotland offers free advice on improving the energy efficiency of your home³. In England, council-run services such as Action on Energy provide communities with advice and support for improving home energy efficiency²³.

How accurate it is when you don't know the details

Accuracy depends on how much of the property record the tool can reach. Where the address matches, the estimate draws on the building's age, construction and EPC rating plus current energy use⁴. Where it does not match, the Energy Saving Trust's own wording is that it can still provide potential savings, but they will not be specific to your home⁵.

The second limit is the householder's own knowledge. Official statistics found that 16% reported knowing their exact rating for their home⁶. A plan built on a guessed rating will be directionally right and numerically loose.

The third limit is the rating system itself. The Scottish Government's consultation states that the current metrics do not accurately reflect the fabric efficiency of a home nor do they support the transition to net zero¹⁶, which is a limitation of the underlying framework rather than of any one calculator. Reform is anticipated, with the final date depending on when the UK Home Energy Model becomes available.

For a householder, the practical reading is that the tool is reliable for ranking and sequencing, and less reliable for predicting a bill to the pound. The site's guide to measuring results after the work sets out how to check the outcome once measures are installed, and baseline your energy use covers establishing the starting figure the plan should be judged against.

Saving, editing and returning to your plan

Whether a plan can be reopened depends on which version produced it. Services that require registration, such as Which?'s, hold the plan against a name and email address⁹, so returning means signing in with the same details. Council and advice service versions are held by the organisation that ran the survey.

Editing the assumptions is part of the process rather than a separate step. The tool asks a short set of questions about the property, and the Energy Saving Trust notes that homes without electric heating can still use its calculators, with a few more questions asked about the home⁵. Correcting the heating type, the glazing or the insulation level moves the plan closer to the actual building.

Downloading follows the same route as the plan itself. HomePlus issues a personalised report and an action plan¹; Homewise issues a tailored retrofit action plan with an indicative EPC rating and a cost breakdown²⁰. Where the tool is run through a council, the report is issued through that service.

Keeping the paperwork matters more than it appears. The site's guide to the paperwork to keep explains why the plan, the quotes and the completion evidence should be retained together, particularly where a grant or a future sale is involved.

Where it fits with other tools: HomePlus, Home Energy Saver and Homewise

Several tools share the same engine and the same underlying data, and the differences are in the surrounding service rather than in the calculation.

Homewise is described as a market-leading tool that helps residents make energy efficiency improvements to their homes¹³, and it gives energy saving advice to help save money on energy bills and boost the energy rating of your home²⁵. HomePlus is the Energy Saving Trust's own consumer-facing route, with the tool as an integral part of its Digital Home Report¹.

The wider advice landscape is being reorganised. The new Home Energy Advice service is intended as a single-entry point for consumer home energy advice on GOV.UK, helping homeowners, landlords and tenants find tailored, impartial and trusted advice on how to heat their homes and make them more energy efficient²⁶. The site's guide to the GOV.UK Find Ways to Save Energy in Your Home tool covers that route, and home energy assessments covers what a paid assessment adds beyond any calculator.

What the tool cannot do, and what still depends on others

The tool produces a plan. It does not produce a certificate, carry out work, or guarantee a saving. An EPC is a formal assessment of a home's energy efficiency¹⁴, and only an accredited assessor can lodge one. The tool's rating is a planning figure.

Meter data is a separate dependency. A home energy monitor can help track electricity use, but it does not replace a smart meter because it cannot automatically send meter readings to a supplier²⁷, and it does not automatically break usage down by appliance²⁷. Households without a smart meter will still need to submit manual meter readings to their energy supplier to avoid getting an estimated bill²⁷. Where a smart meter is fitted, automatic meter readings provide a supplier with monthly, weekly, daily, or even half-hourly readings²⁸, and the household does not need to submit meter readings itself²⁹. Ofgem's guidance on getting help with a smart meter covers the practical route²⁹.

The remaining dependencies are the familiar ones: a grid connection, a supplier, and for gas-heated homes a gas network. The tool reduces dependence on a single installer's judgement, and it makes the sequence of work visible before money is committed. It does not change where the energy comes from. The site's guide to planning a route to household energy independence sets out what would.