..........The power company charge you for electricity in kilowatt-hours..that is 1kilowatt of power (watts) burning for one hour.....so if you leavethat particular fan heater on for one hour, you will use 1.2 kilowatt-hours of power and be charged 1.2 times the rate they charge...similarly a 100watt bulb would burn for 10 hours to make up the one kilowatt......
..that I think is the basic idea though in practice the Kilowatt-hours are converted to Units by some formula and they charge per Unit....see your leccy bill for details..............commoner