Insulation, heat pumps, solar panels and new boilers are often sold on the promise of lower energy bills, and often paid for with a loan. One comparison tells you whether the loan pays for itself month by month.
1. Estimate the monthly bill saving
Use your last twelve months of bills, not the brochure. Take the installer's estimated percentage saving and apply it to your actual annual energy cost, then divide by 12. Be conservative: real savings depend on weather, usage and energy prices.
2. Work out the monthly repayment
Loan amount, interest rate and term give the monthly payment. Include any arrangement fee. Check whether a grant, rebate or tax credit reduces the amount you need to borrow.
3. Compare the two
- Saving is higher than the repayment: the upgrade is cash-flow positive from month one.
- Saving is lower: you're partly financing a home improvement. That can still be worth doing (comfort, home value, a broken boiler that has to be replaced anyway), but budget the difference as a real monthly cost.
4. Check the payback after the loan ends
Once the loan is paid off, the full saving stays with you. A long loan on an upgrade that lasts 20+ years can be reasonable; a long loan on something with a short lifespan rarely is.
Free tools
- Electricity cost calculator
- Loan calculator
- Home renovation budget spreadsheet (free CSV)
- Debt Snowball & Avalanche Payoff Planner
General information, not financial advice.