Ductwork is a system of metal or plastic tubes that carry air throughout a building. If you've ever noticed large rectangular or round tubes running along the ceiling of a basement or seen vents in the walls of your classroom, you're looking at parts of a ductwork system.

Think of ductwork as the lungs and airways of a building. Just as your body moves air in and out through tubes called bronchi, a building uses ducts to move heated or cooled air from a furnace or air conditioner to every room. Without ductwork, only the room with the heating or cooling unit would be comfortable.

The ducts connect to vents (those grilles you see in floors, ceilings, or walls) that let air flow into each room. Return ducts pull air back to be heated or cooled again. In a well-designed system, the ductwork is hidden in walls, ceilings, or crawl spaces, quietly doing its job. When ductwork develops leaks or gets clogged with dust, rooms can become uncomfortably hot or cold because air isn't reaching them as well as it should.