Microwaves heat and cook food. These appliances can sit on countertops or can be mounted under countertops to save space in office breakrooms and professional kitchens. Cooking wattages determine how evenly and quickly a microwave can cook a piece of food. Higher-wattage microwaves cook food faster and more evenly than lower-wattage microwaves. ENERGY STAR-certified appliances use less energy and perform as well or better than unrated appliances, and may contribute to a lower monthly energy bill.