Real numbers for real UK homes
Switching from oil to a heat pump, adding a home battery, buying an EV or changing tariff are big decisions, and most online calculators either hide their maths or exist to sell you something. These are free, plain calculators that show every assumption, so you can put in the quote you've been given and your own usage and see what it really means.
They were built by a UK homeowner working through these decisions himself: replacing an oil boiler with an air source heat pump, planning DIY battery storage charged on a cheap overnight rate, and running two electric cars. The calculators check the things quotes often skip, such as whether an inverter can actually fill a battery in your off-peak window, or what oil price makes a heat pump break even.
How to use them
- Start with your own figures: annual oil use, electricity usage from your bill or smart meter app, and the prices on your tariff.
- Replace the example prices. They're there as a starting point and change often.
- Read the warnings under the results. They flag sizing and supply problems worth asking your installer about.
Everything runs in your browser. Nothing you type is sent anywhere, and your figures are remembered on this device so you can come back to them.