Metered Energy Savings: Paying for Retrofit on Measured Performance

The headline result is a split verdict. The methodologies were found suitable for monthly, weekly and potentially daily savings estimates on UK homes, and suitable for estimating sub-daily savings on portfolios of properties. They were found inadequate for sub-daily savings on individual homes¹. In plain terms, a group of dwellings can be measured hour by hour; a single dwelling cannot.

That matters because retrofit funding still runs largely on modelled assessment. Smart Meter Enabled Thermal Efficiency Ratings are an eligible measure for Warm Homes: Social Housing Fund Wave 3, but only if part of a technology or measure that can be modelled in RdSAP or SAP². The metered route is therefore an evaluation tool bolted onto a modelled scheme, not yet a payment mechanism in its own right.

Why modelled estimates fall short: the confidence barrier

The case for metered savings rests on a documented weakness in modelled assessment. Government research compared modelled energy use with monitoring data specifically to identify inaccuracies in Energy Performance Certificates and propose improvements⁴. The Scottish Government's consultation position is blunter: the current metrics do not accurately reflect the fabric efficiency of a home nor do they support our transition to net zero⁵.

That gap is the confidence barrier. A household is asked to fund insulation, glazing or a heat pump on the strength of a predicted saving, and the prediction is produced by a model whose inputs are a surveyor's assumptions about construction, occupancy and heating behaviour. Where those assumptions are wrong, the predicted saving and the realised saving diverge, and the household carries the difference.

The Energy Saving Trust sets out why realised savings move around so much. Actual savings vary by property type, size and location, existing insulation levels, heating system, occupancy patterns, energy tariffs, installation quality and how people use their home or business after improvements⁶. Those are not marginal adjustments. They are the difference between a payback period that works and one that does not.

Behaviour is part of it. A trial of boiler efficiency advice estimated that if households were to compensate for the lower room temperature, the initial gas saving would be reduced by over 50%⁷. A model that assumes a setpoint will overstate the saving wherever the occupant restores the original comfort level.

Billing accuracy is a separate strand. A case study of a missed meter exchange found a customer who for the previous six months had billed for electricity using estimated readings only⁸. Where the underlying consumption data is estimated rather than measured, any savings calculation built on it inherits the error.

The Metered Energy Savings project: who ran it and the 42 UK homes tested

The Metered Energy Savings project was run by the Energy Systems Catapult, which published its report on 29 October 2022¹. A Welsh Government report on the same body of work followed in July 2024, setting out testing of CalTRACK and SENSEI counterfactual models on 42 UK homes¹. The project's purpose was to establish whether smart meter data could support a metered savings protocol for UK residential retrofits.

The sample is the project's own stated limitation. The report notes that its conclusions ideally require validation on a larger, fully representative sample of UK homes, as this project relied on a small sample of only 42 homes¹. Forty-two dwellings is enough to demonstrate that a method can run; it is not enough to establish how the method behaves across the UK housing stock, with its mix of ages, constructions, heating systems and occupancy patterns.

The wider data environment has changed since. Smart meters are now installed in half of UK properties⁹, and more than 37 million smart meters are installed across over 22 million homes and small businesses in Britain³. Almost 40 million households and small businesses across Britain already use smart meters¹⁰. The measurement infrastructure the project depended on has moved from partial to mainstream.

What data a home needs: smart meter readings, gas and electricity, and 12 months minimum

A metered savings calculation needs a continuous consumption record for the dwelling, covering both fuels where both are used, and long enough to establish a baseline that separates weather from behaviour. Smart meters enable accurate billing by automatically recording energy use in half-hour periods¹¹. That half-hourly record is the raw material.

The two fuels are measured differently, and the difference matters to any calculation. Electricity meters measure the amount of energy units used in the home, these are known as kilowatt hours (kWh)¹². Gas meters measure in cubic metres or cubic feet and your supplier will then convert this to kWh when working out how much you have used¹². A metered savings method therefore has to reconcile a direct energy reading for electricity with a volume reading for gas that is converted downstream.

The data also has a second life. The data you share through your smart meter is used to bill you for the energy you use, offer you new products and services such as new tariffs where permission has been given, and help make the energy system more efficient by recording demand more accurately¹³. For the household, the same record supports the practical side of the exercise: a smart meter can help a household find ways to save money using up-to-date information on your energy use¹³.

Twelve months is the working minimum for a defensible baseline, because a shorter window cannot cover both a heating season and a non-heating season. The project's finding that monthly and weekly estimates are workable implies a baseline of at least that order; a single quarter would leave the counterfactual model fitting weather rather than measuring a retrofit.

What the project found: monthly and portfolio savings work, half-hourly single homes do not

The project's central finding is a resolution limit. The methodologies were found suitable for estimating monthly, weekly and potentially daily savings on UK homes, and suitable for estimating sub-daily savings on portfolios of properties. They were found inadequate for sub-daily savings on individual homes¹.

The reason is signal against noise. At half-hourly resolution, a single dwelling's consumption is dominated by short events: a shower, an oven, a car charging, a thermostat adjustment. The weather-driven heating signal that a counterfactual model needs to isolate is small relative to that variation, so the model cannot distinguish a genuine retrofit saving from ordinary daily life. Stretch the window to a month and the noise averages out; pool many dwellings and the same averaging happens across the sample.

This is why the project's verdict is not a rejection of metered savings but a specification of where it applies. Monthly and weekly savings on an individual home are within reach. Daily savings are described as potentially achievable. Half-hourly savings on one home are not.

The same logic explains why gas is harder to model in summer than in winter. Summer gas consumption is hot water and cooking, a small and weather-insensitive load, so the baseline is thin and any error is proportionally large. Winter gas consumption is dominated by space heating, which tracks outdoor temperature and gives the model a strong signal to fit.

Aggregating homes: how a portfolio produces accurate hourly counterfactuals

Aggregation is the route to sub-daily accuracy. The project found the methodologies suitable for estimating sub-daily savings on portfolios of properties¹, which means the unit of measurement becomes the group rather than the dwelling. Individual half-hourly volatility cancels across the group, leaving the shared weather response that the counterfactual model can fit.

No fixed minimum portfolio size is published, and no figure should be inferred. What the evidence does show is that the method scales with the number of dwellings rather than with the sophistication of the model applied to one. A programme of homes on comparable heating systems, metered continuously and assessed against a common weather baseline, is the shape the finding points to; the project itself did not publish a threshold.

Comparable work in the same period shows the scale at which retrofit programmes operate. Government research on the heat pump transition included concurrent technical audits in 20 homes¹⁵. The Social Housing Decarbonisation Fund will see energy performance improvements to up to 20,000 social housing properties¹⁶. The Buildings Retrofit Pilot states that by improving the energy efficiency of buildings, the Retrofit Pilot will help reduce households and public sector energy bills¹⁷.

The policy context for measurement is a stock that has not been improved fast enough. Citizens Advice research estimates that upgrading 13 million inefficient homes to EPC C could save consumers £24 billion on energy bills, and that an estimated 10 million more homes would have been insulated between 2013-23¹⁸. Metered savings is one answer to the question of how a programme at that scale could demonstrate what it delivered.

What it means for UK households and retrofit funding

For a household, metered savings changes what evidence is available rather than what money is available. No published fact links a metered saving to a payment, a tariff or a grant. The nearest thing is the Warm Homes: Social Housing Fund Wave 3 position: grant recipients may choose to use Smart Meter Enabled Thermal Efficiency Ratings in the evaluation of retrofit, and doing so helps them deliver and receive points under the Innovation Strategic Priority². That is an evaluation credit for a grant recipient, not a payment to a resident.

The independence question is therefore mixed. On one side, metered savings reduces reliance on a surveyor's model and on the assumptions built into it, and it uses data the home already generates. Smart meter data puts a household in control of its energy usage, meaning it can take energy-saving steps to reduce its CO2 emissions¹⁹. At system level, smart meters can reduce fossil fuel use and support the integration of more homegrown renewable energy sources, such as wind and solar, into the energy system²⁰. Smart meters also help to make the energy system smarter by allowing suppliers to offer incentives for households who can reduce their energy use during peak hours, helping to balance supply and demand and reduce pressure on the grid²¹.

On the other side, the dependence does not disappear. The meter belongs to the supplier's network, the readings flow through it, and the conversion of gas volume to kilowatt hours sits with the supplier¹². The household cannot run the calculation itself. The method also remains unvalidated at national scale on a 42-home sample¹, and the funding routes that surround retrofit are still modelled-assessment schemes: the Social Housing Decarbonisation Fund supports the installation of energy performance measures in social homes in England¹⁶, and the Warm Homes Local Grant exists to improve energy efficiency for homes in priority areas²².

For households weighing up what is available now, the practical routes remain the grant schemes rather than metered payment. The Home Energy Grants and Schemes in the UK: The Full Guide sets out the current landscape, and the Warm Homes: Social Housing Fund page covers the scheme in which metered evaluation currently has a formal place. Households in Scotland should note that the Home Report there comprises an Energy Report, a Property Questionnaire and a Single Survey²³, a different assessment structure from the EPC used in England and Wales.