When shopping for a new window-unit air conditioner for your home, understand that not just any size works for any room of the house. If you install too large an air conditioner, yes, it will cool a room very quickly. But air conditioners do two things: They remove heat and humidity from the air. If it cools too quickly, it removes the heat but leave the excess moisture, making it feel very cold and damp. To choose the right unit, measure the room you want to cool and search "air conditioner cooling needs calculator" to find an online tool to help you choose the right size unit. And as always, look for Energy Star-rated models to save the most energy to stay cool this summer.