A fan can help to cool your dog down. The moving air from a fan encourages more evaporation from the mouth when your dog pants. It can also improve convective cooling at the ears to some degree. And, depending on the thickness of your dog's coat, it may also improve convective cooling on the body's surface. Even if the coat is thick, the air moving through the hairs can displace any warm air that has become trapped between them. Many owners find that their dogs enjoy sitting in front of a fan or AC during the summer to cool down.