40 watts for 24 hours is 40 x 24 watt-hours, or 960 watt hours which is 0.96 kilowatt-hours, equal to 0.96 Unit, which costs about £0.12.
What it costs me to run a heater does not depend on how much you are charged, but a 1500 watt heater would use 1500 watt-hours or 1.5 kWh for every hour it is run. Run for 24 hours it would use 36 kWh, also known as 36 units.
0.260kW * 4h * $0.20/kWh = $0.208
The fan has a rated load of 2 kW. It is this wattage times the amount of hours the fan is used times the cost of a kWh in your area that the cost is based on.
The wattage measures an instantaneous power consumption of a load. You get charged by Watt Hours. A typical cost per 1000 watt hours might be around 12 cents.
25 watts * 24 hours = 600 watt hours = 0.6 kwh {1 kilowatt hour = 1000 watt hours} 0.6 kwh * (0.085156 per kwh ) = 0.0510936 or about 5.1 cents
What it costs me to run a heater does not depend on how much you are charged, but a 1500 watt heater would use 1500 watt-hours or 1.5 kWh for every hour it is run. Run for 24 hours it would use 36 kWh, also known as 36 units.
0.260kW * 4h * $0.20/kWh = $0.208
Usually much smaller. A normal freeze plug block heater is about fifty bucks.
The fan has a rated load of 2 kW. It is this wattage times the amount of hours the fan is used times the cost of a kWh in your area that the cost is based on.
The wattage measures an instantaneous power consumption of a load. You get charged by Watt Hours. A typical cost per 1000 watt hours might be around 12 cents.
A 0 Watt bulb does not consume electric power so the cost is zero.
25 watts * 24 hours = 600 watt hours = 0.6 kwh {1 kilowatt hour = 1000 watt hours} 0.6 kwh * (0.085156 per kwh ) = 0.0510936 or about 5.1 cents
To calculate a cost in kW/h a time interval has to be stated. How long is the 400 watt heater going to be on in a 24 hour period. You also have to state what you are being charged from the utility power company per kW/h.
The bulb uses 7.5 watt-hours each hour, or 90 watt-hours if left on for 12 hours. 1 unit of electricity would be used in 11 days at 12 hours per day.
From the details this is probably a UK question. It would use 60 watt-hours of energy every hour, which is 0.06 kWh or units of electricity, and that would cost around 1p.
A 50 watt heater is major over kill for a 3 gallon tank, a 10 watt heater is more than enough for a tank that size. You will nuke your aquarium very quickly the first time the 50 watt heater sticks on, with a 10 watt heater if it sticks on the aquarium temp will only raise a degree or two.
By energy you mean watt hours. So the equation is watts x hours = 1680 watt hrs. Or stated in Kilowatts it would be 1.68 kw hrs. Average cost in USA would be about 18 cents.