What it actually costs to run per day and per year

Take the power in watts, divide by 1,000 to get kilowatts, multiply by the hours it runs to get kilowatt-hours, then multiply by your rate per kWh. A 1,500 W heater running 5 hours a day uses 7.5 kWh, so at a rate of 0.18 per kWh it costs 1.35 a day in whichever currency you are billed.

Multiply amps by volts to get watts first — this is the step people skip, and it matters because the same current means very different power at different voltages. A 12 A load is 1,440 W on a 120 V circuit but 2,880 W on 240 V, so the running cost doubles for an identical amp reading.

The all-in rate from your bill rather than the headline unit rate. Divide the total bill by the kilowatt-hours it covers and you capture supply charges, levies and taxes as well as the energy itself — that is what a kilowatt-hour genuinely costs you, and it is usually meaningfully higher than the advertised rate.

Because a nameplate rating is the maximum draw, not the average. Anything thermostatically controlled — fridges, freezers, air conditioners, compressors, heaters — cycles on and off, so it might only draw full power a third of the time. Treat the result as the ceiling for continuous running and scale it by the duty cycle.

A 1,500 W heater uses 1.5 kWh for every hour it runs — 7.5 kWh over a 5-hour evening, about 225 kWh a month at that usage, and roughly 1,080 kWh a month if it never goes off. Multiply by your rate per kWh for the cost. The gap between those last two figures is why portable electric heat is the most expensive way to warm a room.

Yes — running cost is often the argument that closes the job. Showing the annual cost of the old unit against the replacement makes the payback concrete in a way that efficiency ratings do not, whether that is a heat pump against resistive heat, LED against halogen, or a properly sized compressor against an overloaded one.