Insulation Energy Savings Calculator

How this calculator works

This calculator works in ranges rather than single figures, because real quotes, yields and tariffs genuinely vary that much. It starts from typical UK price, output and savings ranges drawn from published 2026 industry guides and official scheme documentation, then scales them by the quantities you enter and adjusts them for each choice you make below. The result is a low-to-high band that a realistic outcome is likely to fall within, not a promise of the figure you will achieve.

A typical semi-detached home combining loft insulation, cavity wall insulation and draught proofing saves roughly to a year at 2026 energy prices for a combined outlay of to , a three to five year payback that outperforms almost any other home investment. The figures here follow the Energy Saving Trust’s approach of quoting typical savings per measure for a gas-heated home, scaled for your home size and fuel.

Loft insulation

Going from an uninsulated or thinly insulated loft to the recommended 270 mm saves roughly to a year for a typical semi at 2026 gas prices, with the biggest savings where there is currently least. Topping up from 100 or 150 mm saves proportionally less, roughly a third to a half of the full figure.

Cavity wall insulation

Filling unfilled cavity walls saves roughly to a year for a typical home, since walls are the biggest single heat loss route. The measure only applies to homes with suitable unfilled cavities, broadly those built between the 1920s and 1990s that have not already been treated.

Solid wall insulation

Insulating solid walls saves the most of any single measure, roughly to a year for a typical home, because uninsulated solid walls lose heat fastest of all. It is also the most expensive measure to install, which is why its payback is measured in decades rather than years and it is usually justified by comfort and refurbishment as much as by the bills.

Floor insulation

Insulating a suspended ground floor saves roughly to a year for a typical home, a modest bill saving with an outsized comfort effect, since cold floors and skirting draughts are what people actually feel.

Draught proofing

Professional draught-proofing of doors, windows, letterboxes and the loft hatch saves roughly to a year and costs only to , giving it a payback measured in a couple of winters. It also makes every other measure feel better, since draughts are the difference between warm air and warm-feeling rooms.

Home size

Savings scale with how much heat the home loses: detached houses expose more wall and roof and heat larger volumes, so each measure saves roughly 40 percent more than in a semi, while flats and small terraces, sheltered by neighbours, save less. Published figures are usually quoted for a gas-heated semi, which is this calculator’s baseline.

Heating fuel

Every kWh of heat that insulation keeps in is a kWh of fuel not bought, so savings scale with the fuel price: gas is the baseline at around 6 pence per kWh under the 2026 caps, oil is similar but volatile, LPG costs meaningfully more, and direct electric heating at 24 to 26 pence per kWh roughly doubles every saving figure, which is why insulation is most urgent of all in electrically heated homes.

What else affects the figures

Savings interact rather than simply stack: each measure reduces the heat loss the next one works on, so a fully combined programme saves somewhat less than the sum of its parts, a few percent between two measures and more across many, and this calculator’s ranges are wide partly to absorb that. Real results also depend on behaviour, since some households take the benefit as lower bills and others as warmer rooms, both perfectly good outcomes. Savings rise and fall with energy prices, so every figure here moves with the Ofgem cap, and remember the capital side has substantial support: ECO4 and the Great British Insulation Scheme fund many of these measures partly or fully for eligible households, at which point the payback becomes immediate.

Certification, planning and grid connection

If a calculation here prompts a project, Building Regulations Approved Document L is the standard the work should meet, with U-value targets for each element, and installers registered with TrustMark or a competent person scheme can self-certify compliance. Check grant eligibility before paying for anything: ECO4 runs to 31 December 2026 and the Great British Insulation Scheme continues alongside it, both funding measures partly or fully for qualifying households, and domestic insulation carries 0 percent VAT until 31 March 2027 in any case. An EPC assessment before and after larger projects evidences the improvement for future buyers and lenders.