Return on investment calculator

How payback is worked out

Payback here is the net installation cost after the £7,500 grant divided by your estimated annual running-cost saving. It's most meaningful when replacing oil, LPG or electric heating. For mains gas, running costs are roughly level, so there often isn't a bill-based payback — the return is the grant, comfort and carbon, which this simple sum can't capture. Figures ignore future energy-price changes.