Explainers

The device pages answer one appliance each. These answer the questions that sit across all of them — where the numbers come from, and what they leave out.

• A space heater is 100% efficient, and that is the problem

  Every electric heater turns all of its electricity into heat, which sounds like a perfect score and is actually the worst one available. The arithmetic, with published prices and the month they belong to — and the break-even that decides it.

• The wattage on the label is four different things

  A television, a fridge, an iron and a kettle all carry a number in watts, and it means something different on each of them. Three of the four cannot be turned into a yearly cost the way every other site does it — and one of them does not depend on the wattage at all.