Question: how much does it cost to run an electric heater all day?
Answer: So a 3kW heater will use 3kW (3000 watts) per hour and cost roughly 43 pence to run* or £3.43* for 8 hours. The power rating (watts/kWs) will dictate the running costs; the higher the watts the more it costs to run. For a quick comparison see sust-it's Electric Heating Cost Calculator.