Insulation is installed inside heating and cooling ducts to keep the air inside warm or cool despite surrounding temperatures. It may also be used to dampen the sound of air rushing through the ducts, which may cause a rattling or rumbling noise. This function is especially useful in buildings where this noise would be disruptive. Insulation may be added to an entire line of ducts, or it may just be installed in areas where the most potential for heat loss or noise is present.
What kind of insulation is used in heating and cooling ducts?
The type of insulation used most frequently in ducts is fiberglass duct liner. Fiberglass insulation for ducts is made of similar materials to the fiberglass insulation inside your walls. Fiberglass is used because it is a poor conductor of heat, so warm or cool air will not transfer through it easily. A layer of fiberglass inside the walls of ducts will has the ability to minimize the transfer of sound, which dampens noise transfer.
Thickness and density of fiberglass duct liner will vary according to the pressure of the air coming from a heating or cooling unit, and the level of heat transfer or noise that needs to be contained. Fiberglass liner for ducts may range in thickness from one half to two inches, so the duct must be increased in size according to the thickness of the insulation, so that the amount of air space inside the ducts is equal to that of non-insulated duct. The amount of space inside the duct is the most important for proper air flow, so the appropriate inside measurements must be maintained.
How is insulation applied to the inside of ducts?
Insulation is applied before the ducts are assembled. While the ducts are still flat pieces of metal, sheets of fiberglass duct liner are cut to size to fit the flat metal. Adhesive is applied to the metal, and the insulation is carefully laid in place. Metal pins are then used to reinforce the adhesive. They may be welded to the metal, or pressed into the surface of the metal by special machinery. A sealant is then applied to the ends of the duct and to any place where the fiberglass surface has been cut. This prevents random fiberglass fibers from escaping and blowing through the ducts.
Although they are not used as frequently now as in the past, ducts made of reinforced fiberglass have been used in areas requiring additional noise suppression. Because of their less sturdy composition, they cannot be used in large commercial applications, and are not used in homes because of possible air quality issues.
For more information about duct insulation options or to find out if you should insulate your ducts, contact a company like Allied Air Conditioning & Heating Corp.