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Heating, ventilating, and air conditioning a building is, in a forced air system, accomplished using ductwork. Ducts are a series of sectioned conduits, or tubes, which convey either heated or cooled air from the furnace or air conditioner, throughout the building. These ducts, along with the actual furnace and air conditioning unit, are ordinarily thought of as the building’s heating, ventilation and air conditioning (HVAC) system. Hard pipe, used to transfer water or gas, is not considered ductwork.
The piping or tubing commonly used for ductwork may be manufactured from tin, or sheet metal, fiberglass, or flexible plastic. A type of flexible ductwork may be manufactured from vinyl-encased insulation, through which a coiled wire is inserted. This flexible ductwork is popular due to its ease of installation, and its insulating properties.
Because of its importance in the overall utility, and livability of a particular structure, ducts are often among the first items to consider when designing a new building, or when purchasing an existing structure. Attention to HVAC systems, ensuring constant and efficient performance, is vital to proper building maintenance. A common problem with air ducts is that any contaminants in the air flow will be concentrated by the ductwork, and disbursed throughout the building. Frequent duct cleaning is essential to reduce this occurrence.
An example of an elementary duct would be a simple fireplace chimney. The brick chimney surrounds a tube made of tempered ceramic tile, and is considered a duct. This duct conveys smoke – and altogether too much valuable heat – from the fireplace or wood stove, to be disbursed outside the building.
Ductwork usually consists of a plenum; the actual tubing, or conduit; and a register, or discharge fixture. The plenum is the entry end of the ducting, usually located at the source of air distribution, the furnace or air conditioner. The ducts, the tubes or pipes that convey the tempered air, are usually hidden between the walls, and run into every room in the structure. The registers, located in the floor, walls, or ceilings of a room, are the discharge ends of the ductwork, where the air is blown into the room. A distribution box may be located approximately halfway along the duct system to assist in redirecting the airflow.
Additionally, there is a duct system that is configured to return air displaced by heated/cooled air to the furnace, or air conditioning unit. This air-return ducting is ordinarily not as extensive as the delivery system. Displaced air can be collected and returned to the HVAC unit from a more centralized location among a number of heated or cooled rooms.