How Does a Duct System Work? How does a duct system work, and why is it so important? The duct, or air distribution, system used in cooling and heating your home is a collection of tubes that distributes the heated or cooled air to the different rooms. This branching network of round or rectangular tubes—usually constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite—is found within your home. The duct system is designed to supply rooms with air that is “conditioned”— that is, heated or cooled by the heating, ventilation, and air conditioning (HVAC) equipment— and to circulate or return the same volume of air back to the HVAC equipment. Typical air-duct systems lose 25 to 40% of the heating or cooling energy put out by the cooling and heating system. Leaks, one way in which conditioned air is lost in the duct system, make the HVAC system work harder, thus increasing your utility bill. In addition, duct leakage can lessen comfort and endanger your health and safety. Your duct system has two main air-transfer systems— supply and return. The supply side delivers the conditioned air to the home through individual room registers—what you feel blowing out of the registers. The return side withdraws inside air and delivers it to the air handler of your central system. All of the air drawn into the return duct(s) is conditioned and should be delivered back through the supply registers. Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. What is a ducting system? Ductwork, ducts, or ducting, are conduits, or tubes, that typically form part of a ventilation system, used to convey air throughout a building. Materials Ducts can be made out of the following materials: Galvanized steel Galvanized mild steel is the standard and most common material used in fabricating ductwork because the zinc coating of this metal prevents rusting and avoids cost of painting. For insulation purposes, metal ducts are typically lined with faced fiberglass blankets (duct liner) or wrapped externally with fiberglass blankets (duct wrap). When necessary, a double walled duct is used. This will usually have an inner perforated liner, then a 1–2" layer of fiberglass insulation contained inside an outer solid pipe. Rectangular ductwork commonly is fabricated to suit by specialized metal shops. For ease of handling, it most often comes in 4' sections (or joints). Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suit, but the most common stock sizes range evenly from 4" to 24" with 6"-12" being most commonly used. Stock pipe is usually sold in 10' joints. There are also 5' joints of the non-spiral type pipe available, which is commonly used in residential applications.
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- Fall '19
- Heating, ventilating, and air conditioning, Duct System Work