Most homes in Japan do not use a central heating system, so in the winter, rather than heating up the entire house with an air conditioner, many people use a traditional piece of furniture known as a kotatsu. A kotatsu is a low table with a small electric heater built into the bottom, one thick blanket around the edges and another on the floor to trap heat inside. This keeps the inside of the kotatsu cozy and warm so people can spend the day sitting, eating, reading, or sleeping in comfort.