A Refrigerator is a cooling appliance comprising of a thermally insulated compartment and a mechanism to transfer heat from it to the external environment, cooling the contents to a temperature below ambient. Refrigerators are extensively used to store foods which deteriorate at ambient temperatures, spoilage from bacterial growth and other processes is much slower at low temperatures. Refrigerator maintains a temperature a few degrees above the freezing point of water. It replaced the common icebox and freezers keep their contents frozen. They are used both in households and for commercial use. Most freezers operate at around -18 °C (0 °F). Domestic freezers can be included as a compartment in a refrigerator, sharing the same mechanism or with a separate mechanism or can be standalone units. Domestic freezers are generally upright units, resembling refrigerators or chests resembling upright units laid on their backs.