Gas service at your house begins at the gas meter. The gas flows through iron pipes, steel pipes, and poly pipes under ground to your house. Gas enters the house and then goes up into your attic in iron pipes. In the attic the pipes may supply gas to a furnace and a water heater.
The example we are showing here is the gas service and distribution in a typical residence with a slab foundation. In other types of structures the gas service lines may be under the floors. After the gas piping enters the attic it drops down in iron pipes inside the walls to provide service to ranges, dryers, water heaters, furnaces, and fireplaces. With this complex system of piping, pipe fittings, valves, and appliances, there is always a potential for a gas leak.