A gas furnace uses natural gas to emit heat into your home. Gas combusts inside the heat exchanger, to create heat. A good furnace efficiently emits that heat throughout your home. When homeowners choose a gas furnace over an electric furnace, it’s often because of how fast they work to heat your home. Gas furnaces typically last for two decades with good use and are better for colder climates, as they tend to heat up fast. This type of furnace is difficult to install because there is a major safety factor. It deals with natural gas, which is a highly combustive element.