This chart will help you determine the wattage capacity you need, based on the type and quantity of items you plan to operate. Example: The 6,000-Watt DeVilbiss Generator shown can run a 20,000 BTU air conditioner and a refrigerator/freezer with power to spare. It has an 11-horsepower Briggs & Stratton gasoline engine and can operate for 9.1 hours at half-power load and 6.3 hours at full-load without refueling.