Furnaces are heating systems that are used to heat buildings and homes. They work by burning fuel such as gas, oil, or propane, which heats up air that is then blown through ductwork and distributed throughout the building. Furnaces are commonly used in colder climates to provide warmth during the winter months. They come in different sizes and efficiency levels to accommodate different heating needs and fuel sources, and can be a cost-effective and reliable way to keep buildings comfortable in cold weather.