First you must consider what you want or need to power with a generator. Most portable units offer 4,000 to 12,000 watts. Consider that appliances such as refrigerators, freezers or large items like those need 700-800 watts each, but that doesn’t count the startup wattage needed (usually double, or maybe triple). Smaller items such as televisions or a microwave may need just a few hundred watts. A natural gas furnace may need about 1,400 watts to get started. Home air conditioners need considerably more to start and power. Factor in these considerations before purchasing.