Ondol is the traditional under floor heating system which has been used in Korean peninsula where the winter is very severe. The heat from the stove in the kitchen goes through the pathway under the floor. They use the firewood or straw for the stove. The entrance of the house is made smaller to prevent cold air coming into the house. They sleep on the warm floor with the mat and they do not need to wear room shoes. In the modern Korean house, Ondol is still used for hot water.