Boiler Efficiency Calculator 2026 | Calculate Your Savings

Worked example

Example inputs, chosen only to show the arithmetic: a current boiler efficiency of 75%, a new boiler efficiency of 92% and 11,500 kWh of energy use a year (the typical medium-home gas figure quoted in the FAQ below).

1. Efficiency gain: (92 − 75) ÷ 100 = 0.17.
2. Annual saving: 0.17 × 11,500 kWh × £0.073 per kWh = £142.72, shown as £143 a year.
3. CO₂ reduction: 0.17 × 11,500 kWh × 0.182 kg per kWh = 356 kg a year.
4. Payback: £3,000 ÷ £142.72 = 21 years.

How this is calculated and sources

The calculator takes the gap between the two efficiencies as a share of your annual energy use, then values it at £0.073 per kWh of gas and 0.182 kg of CO₂ per kWh, and divides an assumed £3,000 boiler cost by the saving. It does not look up your tariff or fuel type. The 0.182 kg figure is the UK Government GHG Conversion Factors 2026 (DESNZ) factor for natural gas. The £0.073 gas price and the £3,000 boiler cost are assumptions used by this calculator. The output is a rough estimate, not a quote. Under ECO4, eligible households do not pay for the boiler, so the payback figure only applies if you pay for it yourself.