A watt is a unit of power, specifically the amount of power produced by sending a one ampere current through a one volt electric potential. Wattage is then multiplied by the amount of time the power is flowing to determine watt-hours, or usually kilowatt-hours, which is what the electric company charges you for. If you don't know the wattage of any particular appliance, you can multiply the amperage, which has to be listed on the device, by 120, which is the standard voltage in the United States.
The kitchen is one of the main energy consumers of a house. A frost-free 16 cubic foot refrigerator will consume about 725 watts, and you can adjust that up or down slightly for larger or smaller refrigerators. A dishwasher is going to consume around 1,200 watts, but if you run the dishes through a drying cycle as well, this can jump to 2,400 watts. A coffee maker, toaster and toaster oven will all consume between 800 and 1,400 watts. Microwave ovens can consume as few as 750 watts, and they can also reach up into the 2,000 range, depending on the power of the model.
Living Room Appliances
You might think of your TV as one of the main energy hogs in your house, but even a big 50-inch projection TV will only pull about 170 watts. A flat screen TV will only use about 120 watts and your DVD player will only use between 20 and 25. A stereo system can range between 70 and 400 watts, depending on the number of speakers and features. A desktop computer will consume a little less than 300 watts, with over half of the being the monitor. A laptop computer will only consume around 50 watts.
Appliances that create heat are some of the biggest energy users. A clothes dryer will consume between 1,800 and 5,000 watts, a hair dryer will consume between 1,200 and 1,875 watts and a clothes iron will consume between 1,000 and 1,800 watts. Your water heater is probably the biggest consumer in your house, with most using between 4,500 and 5,500 watts. Your clothes washer will only consumer between 350 and 500 watts, and your vacuum cleaner will use between 1,000 and 1,440 watts.
Additional Power Considerations
Two huge considerations need to be made when determining your overall power needs: the reactive load requirements and low-power draws. A reactive load is the amount of wattage an appliance will draw when it has to start up a motor. Once the motor is running, the appliance uses its normal wattage, but when it is starting up it draws up to double the amount of wattage. Low power drains, sometimes called ghost loads, occur when appliances are in standby or ready mode and still draw some power. For example, you microwave might need 1,500 watts while it is running, but if you only use it for two minutes a day, that's not a lot of power. However, it can also draw between two and three watts while in standby mode. This constant draw of power, spread over many appliances, can add up.