This green home savings calculator puts six upgrades side by side: loft insulation, cavity wall insulation, solar panels with or without a battery, an air source heat pump and switching to an electric car. Choose your home type, add your own energy use, and see the upfront cost, yearly saving and payback years for each. It works as a loft insulation calculator, a solar savings calculator and a heat pump running cost check.
Work out your payback
The form is filled in with a typical semi-detached home and its results are shown below. Change anything that doesn’t match your home and press Compare.
For a semi-detached house, loft insulation (none to 270mm) pays back first: about 3.2 to 3.9 years.
Loft insulation (none to 270mm)
Pays back first- Upfront cost
- £750
- Yearly saving
- £190 to £233
- Payback
- 3.2 to 3.9 years
Energy Saving Trust figure for a gas-heated semi-detached house, up to the same energy saving priced at today’s gas cap. Lasts around 40 years.
Solar panels
- Upfront cost
- £7,600
- Yearly saving
- £920
- Payback
- 8.3 to 9 years
Typical 4.5 kWp system near London, home half the day, selling spare power through the Smart Export Guarantee. The longer payback is the Energy Saving Trust’s own figure.
Cavity wall insulation
- Upfront cost
- £2,200
- Yearly saving
- £200 to £245
- Payback
- 9.0 to 11.0 years
Energy Saving Trust figure for a gas-heated semi-detached house, up to the same energy saving priced at today’s gas cap.
Solar panels with a battery
- Upfront cost
- £12,200 to £15,600
- Yearly saving
- £920 to £1,181
- Payback
- 10.3 to 17.0 years
A 5 kWh battery adds at most £261 a year (filled from the panels and emptied every single day), so on its own it takes at least 17.6 years, against a 10 to 12-year battery life.
Air source heat pump
- Upfront cost
- £4,500
- Yearly saving
- £35 to £186
- Payback
- 24.2 to over 50 years
Replacing your gas boiler: 9,500 kWh a year now costs £865 including the standing charge you would drop; a heat pump would cost £680 to £830 a year to run on a standard tariff. Price is after a £7,500 Boiler Upgrade Scheme grant.
Switching to an electric car
- Upfront cost
- Enter the price gap
- Yearly saving
- £973 to £1,273
- Payback
- Depends on the price gap between the cars
10,000 miles a year, charging at home, standard tariff, against the Energy Saving Trust’s petrol cost. The lower figure includes the 3p a mile road charge due from April 2028.
Estimates for general information only, not advice. See Important information below.
Written by Anthropic’s Claude AI from the figures above. What you enter is sent to it to write the explanation, so please don’t include personal details.
The figures behind the calculator
Insulation: typical cost / yearly saving
| Home | Loft, none to 270mm | Loft, 120mm to 270mm | Cavity wall |
|---|---|---|---|
| Detached house | £1,100 / £360 | £800 / £35 | £3,900 / £380 |
| Semi-detached house | £750 / £190 | £600 / £17 | £2,200 / £200 |
| Mid-terrace house | £650 / £140 | £500 / £13 | £1,100 / £110 |
| Detached bungalow | £1,200 / £350 | £800 / £35 | £1,700 / £160 |
| Mid-floor flat | No figure | No figure | £950 / £110 |
Energy Saving Trust, gas-heated homes, unsubsidised installation, fuel prices as of July 2026 (loft, cavity wall). EST prices gas at 6.5p/kWh (its data notes); the calculator also shows the same energy saving at the 7.97p cap.
Solar panels: yearly saving with / without export payments (EST payback with export)
| Near | Home all day | Home half the day | Out all day |
|---|---|---|---|
| London | £930 / £330 (9 yrs) | £920 / £270 (9 yrs) | £900 / £200 (9 yrs) |
| Manchester | £810 / £310 (10 yrs) | £800 / £250 (10 yrs) | £740 / £190 (11 yrs) |
| Aberystwyth | £870 / £320 (9 yrs) | £870 / £270 (9 yrs) | £840 / £190 (10 yrs) |
| Stirling | £740 / £290 (11 yrs) | £720 / £240 (11 yrs) | £680 / £180 (12 yrs) |
Energy Saving Trust, solar panels (page updated 1 October 2026): a typical 4.5 kWp system costs around £7,600; figures are for a four-bedroom detached home at July 2026 prices. Export payments are typically around 12p a unit. Batteries: a 5 kWh system costs around £4,600 and battery storage tends to cost £5,000 to £8,000, lasting 10 to 12 years (battery storage). EST does not publish a battery saving, so we show only a best-case ceiling.
Air source heat pump
| Replacing | EST yearly saving, three-bed semi |
|---|---|
| Gas boiler | −£110 to £220 on a standard tariff; £4 to £330 with no gas standing charge; £204 to £530 on a heat pump tariff with no gas standing charge |
| Oil boiler | −£90 to £260 standard tariff; £110 to £460 heat pump tariff |
| LPG boiler | £290 to £780 standard; £360 to £850 with no standing charge; £560 to £1,050 heat pump tariff |
| Electric heating | £800 to £1,200 standard tariff; £1,000 to £1,400 heat pump tariff |
Ranges run from the most to the least efficient old system. Energy Saving Trust, air source heat pumps (updated 23 September 2026): typical installation around £12,000, July 2026 prices. Grant: £7,500 in England and Wales, plus £1,500 until March 2027 for homes heated by oil or LPG with no mains gas (GOV.UK Boiler Upgrade Scheme). The calculator works out your own running cost from your fuel use: an 84% efficient boiler (as quoted from the government-funded Electrification of Heat trial by the Heat Pump Association) and a heat pump efficiency of 2.53 to 3.09, median 2.80 (Energy Systems Catapult). EST’s research puts the cost of a new boiler you no longer need at about £3,700 (the gap between its £4,200 and £500 switch costs in Flexible futures).
Electric car: cost of 220 miles
| Fuel | Cost | Per mile |
|---|---|---|
| Petrol | £45 | 20.5p |
| Home charging, standard tariff | £17 | 7.7p |
| Home charging, EV tariff | about £8 | 3.6p |
| Public fast charging | £37 | 16.8p |
Energy Saving Trust, charging electric vehicles and electric vehicles (road charge of 3p a mile for electric cars from April 2028). Petrol at 175.28p a litre: DESNZ weekly road fuel prices, week of 12 October 2026.
Energy prices
Ofgem price cap, 1 October to 31 December 2026, Direct Debit, Great Britain average: electricity 26.32p/kWh and 54.83p a day; gas 7.97p/kWh and 29.68p a day. Typical use of 9,500 kWh gas and 2,500 kWh electricity a year: Ofgem, from 1 July 2026. Figures checked 16 October 2026.
How it works and where the numbers come from
Costs and savings for insulation, solar panels and heat pumps come from the Energy Saving Trust, whose figures are based on fuel prices as of July 2026. Energy prices are the Ofgem price cap for 1 October to 31 December 2026: 26.32p per kWh for electricity and 7.97p for gas. The £7,500 Boiler Upgrade Scheme grant for England and Wales is taken from GOV.UK. Heat pump running costs use efficiency measured in the Electrification of Heat trial, reported by Energy Systems Catapult. Car costs use Energy Saving Trust charging figures and the government petrol price for 12 October 2026. Payback is upfront cost divided by yearly saving. Uncertain figures are shown as a range.
A worked example
Take a gas-heated semi-detached house near London with an empty loft, unfilled cavity walls and Ofgem's typical 9,500 kWh of gas a year. Loft insulation costs about £750 and saves £190 to £233 a year, so it pays back in 3.2 to 3.9 years. Solar panels cost about £7,600 and save around £920 with export payments, taking 8.3 to 9 years. Cavity wall insulation takes 9 to 11 years. After the grant, a heat pump on a standard tariff saves only £35 to £186 a year against gas, so its payback runs from 24 years to more than 50.
FAQ
Why does loft insulation usually come out first?
It is cheap, and an uninsulated home loses around a quarter of its heat through the roof.
Is a battery worth adding to solar panels?
Usually not, on savings alone. A 5 kWh battery filled and emptied every day would save at most about £261 a year with export payments, yet costs around £4,600 and lasts 10 to 12 years.
What is the heat pump running cost compared with gas?
For 9,500 kWh of gas, a heat pump would use roughly 2,580 to 3,150 kWh of electricity, about £680 to £830 a year at the cap rate. Heat pump tariffs and dropping the gas standing charge improve this.
Does the electric car saving include the new road charge?
The lower figure does. From April 2028 electric cars are due to pay 3p a mile, which adds £300 a year at 10,000 miles.
Important information
This tool gives general information and estimates only. It is not financial, tax, legal, medical or other professional advice, and it does not take your personal circumstances into account.
Savings and payback times are estimates. Real results depend on your home, usage and installer. Get a survey and written quotes from accredited installers, and check grant eligibility on GOV.UK before you commit.
The figures are based on the published sources and dates shown on this page. Prices, rates and rules change, so they may be out of date by the time you read this. Check them with the supplier, provider or official source, or ask a qualified professional, before you make a decision.
The AI-written explanation is produced automatically by Anthropic's Claude from the figures on this page. It can contain mistakes and should not be relied on.
We don't keep what you enter. If you use the AI explanation, what you entered is sent to Anthropic so it can write it.
You use this tool at your own risk. Saving Our Planet accepts no responsibility for any loss, cost or decision made as a result of using it, as far as the law allows.