Air conditioning ducts distribute air throughout a building and are a central component of HVAC systems. They carry cool air in summer and heated air in winter, along with ventilation needs. Ducts come in different sizes, shapes, and materials. The supply duct carries fresh air from the unit to each room, while the return duct carries warmer air back to the unit for cooling. Insulation can help prevent noise and condensation.
An air conditioning duct is a type of tube or tunnel used to distribute air throughout a structure. Duct systems, known as ductwork, are a central component of a building’s heating, ventilation, and air conditioning (HVAC) system. In most systems, there is only one set of ductwork, which is used to carry cool air in the summer and heated air in the winter, along with the air needed for general ventilation needs. Air conditioning duct is only used with central air units and is not needed for homes that rely on split systems or ductless air conditioning.
To understand the function of the air conditioning duct, one must first understand how a central air system works. First, a system of intake grilles or slots draws fresh air from outside into the central air unit. The air is cooled, then introduced into a duct system, where it is distributed in the various rooms. Fresh air enters the rooms through terminal air units installed at the end of each duct line, which generally take the form of diffusers or grilles. This network of ducts that carry fresh air from the unit to each room is called supply ducts.
Of course, to maintain a relatively stable air pressure in any room, some air must be removed to make way for this new supply of fresh air. A second set of ducts, called a return duct, is used to carry warmer air from each room to the air conditioning unit for cooling. The air enters the return ducts through exhaust grilles or registers in each room. It returns to the unit, where it is more easily cooled for redistribution or released outside the house and exchanged for fresh air.
The air conditioning duct is selected based on its size, shape and material. The size of a duct is based on the air pressure in the home, the type of HVAC equipment used, and the cooling needs of the occupants. Round ducts are considered to be the most efficient, allowing for a greater volume of air movement per unit of duct, yet are rarely used. Instead, builders rely on square or rectangular ducts, which fit more easily into narrow ceiling and wall cavities. Spiral duct, which resembles corrugated pipe, is the least efficient shape of the three, but is often chosen for its appearance when the duct will be left exposed.
There are three basic materials used to manufacture the air conditioning duct. Galvanized steel has historically been the most widely used due to its strength and resistance to rust and corrosion. While still the material of choice, steel is associated with high levels of air leakage, which can leave a system unbalanced. Flexible ducts made of plastic-coated wire frames are commonly used on short runs or at transition points to reduce pressure losses. Fabric ducts are becoming increasingly popular due to their quick installation, even air distribution and good looks.
When metal duct is used, it is often insulated to help reduce noise and minimize condensation. Insulation can also help prevent ducts from drawing air into your home, which leads to uneven temperature levels and wasted energy. Many metal ducts have built-in insulation along the inside walls. Air conditioning ducts without integral lining are often wrapped with fiberglass or similar types of insulation. However, this additional duct lining can be problematic for installation in tight spaces, as it can increase the size of the duct by several inches on each side.
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