It is very easy to calculate the amount of heat energy produced by a 1500-w heater that is connected to a 120-volt line. First, we need to convert watts into kilowatts by dividing 1500 by 100. Next, multiply this number (0.75) times hours (2). This gives us the answer in kilowatt-hours: 75 kilowatt-hours. Some common types of heaters that are connected to a 120-volt line include 1500 watt, 200 watt and 2500 watt. These numbers can be used as an estimate for how much energy will be produced by the type of heater listed above in hours given the same conditions (regardless whether it is day or night). The average person uses about 400 kilowatt-hours per month on heating costs so you would need about 24 hours of usage with this 1500-w heater to equal one monthly bill. However, not all days have exactly 24 hours and some seasons don’t “average” out to save money every time because winter nights may require more use than summer months. You should also take into account your personal preferences