How we work out our estimates
Every figure on this site comes from a published source with a date attached. Where we cannot find a figure we trust, we say so rather than estimate one. This page explains where the numbers come from and what they can and cannot tell you.
We use measured savings, not advertised ones
Our savings come from the government’s National Energy Efficiency Data Framework, which compares metered energy use before and after a measure is installed against a control group of households who installed nothing. It describes what people actually saved.
These figures are often much lower than the ones you will see advertised. Loft insulation is the clearest example: the measured median saving is about 3% of a household’s gas use, roughly £26 a year at current prices, against figures of £150 or more quoted elsewhere. The main reason is that most lofts already hold some insulation, so a new installation is usually a top-up, and the second hundred millimetres saves far less than the first.
We would rather show you the smaller, real number.
Some households save nothing at all
For every measure in that dataset, more than a quarter of households used more energy after installing it. Partly this is rebound — a home that was too expensive to heat properly becomes affordable to warm, and people are warmer rather than cheaper, which is a real benefit but not a saving. Partly it is ordinary variation in weather and occupancy.
We say this on every recommendation it applies to, because an estimate presented without it reads as a promise.
What we cannot tell you
What the work will cost. There is a published government dataset of solar installation costs, drawn from real certified installations, and we use it. For insulation, heat pumps, batteries and glazing there is no equivalent source we can stand behind, so we do not put a price on them. That means we cannot give you a payback for those measures either. Get two or three quotes — the price you are offered is what decides whether the work is worth doing.
Whether a heat pump will cut your bills. We can tell you exactly what you would save by removing your gas meter, because a standing charge is a fixed daily amount. We cannot tell you what happens to your cost per unit of heat, because that depends on how efficiently your particular system is designed and run, and on the tariff you move to. At today’s prices those two roughly cancel out, so most of the difference comes from your tariff and your standing charges rather than from the technology.
Two energy prices, not one
We hold the current Ofgem price cap, which describes what you pay today, and a separate long-run assumption used for anything spanning years. They are not the same number. Electricity is currently zero-rated for VAT until the end of March 2027, and anchoring a twenty-year payback to a temporary rate would overstate the return on everything we suggest.
Why the total is less than the sum
Each measure is shown with what it would save on its own. The combined total is smaller, because improvements interact: insulating your loft reduces the heat a heat pump would then have to supply. Adding up the individual figures would promise you a saving that no combination of the work can actually deliver, so we do not.
Where we cover
England and Wales. Scotland and Northern Ireland run entirely separate schemes — the Boiler Upgrade Scheme does not exist there — so if you are outside England and Wales we will tell you we do not cover you rather than show you a grant you cannot get.
How current this is
Every figure carries the date it was last checked against its source. An automated check runs nightly and flags anything going stale, anything whose scheme is about to close, and any price cap period that has ended. Schemes change often: the Great British Insulation Scheme closed in March 2026 and ECO4 ends in December 2026.
What this is not
This is not a survey, a quote, or a substitute for professional advice. Only an installer’s heat loss survey can tell you whether your home suits a heat pump. We are not a government body and have no connection to any of the schemes described.