Forced-air gas heating systems are used in central air heating/cooling systems for houses. An air conditioner is an Appliance, System, or mechanism designed to extract Heat from an area via a Refrigeration cycle Sometimes the system is referred to as "Forced hot air". Generally, they have a furnace heated by natural gas that pushes hot air through duct-work, then through vents to heat a building. A furnace is a device used for Heating The name derives from Latin fornax, Oven. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, A climate-control device (e. g. , thermostat) regulates and controls the usage of the furnace. A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint A digital thermostat can be programed to activate the gas furnace at certain times. For example, a resident may want the temperature in their dwelling to rise 15 minutes before returning from work. This will conserve energy, expenses and natural resources. Natural resources are naturally occurring substances that are considered valuable in their relatively unmodified ( natural) form The natural gas is fed to buildings from a main gas line submerged a few feet beneath the earth, most likely running under and parallel to a street. The duct work supplying the hot air (and sometimes cool air if an AC unit tied into the system) can be insulated, or not insulated. Residential and commercial buildings located in rural and remote areas do not often use forced hot air systems. This is due to the financial impracticality of running natural gas lines many miles past areas of relative dense habitation. Usually these rural and remote buildings utilize oil heat, which is delivered by a truck. Heating oil, or oil heat, also known in the United States as No When reading ads for houses for sale in the MLS, this is abbreviated as FAG. A Multiple Listing Service ( MLS) (also Multiple Listing System or Multiple Listings Service) is a group of private databases which allows Real estate