Duct Insulation

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There are three purposes for duct insulation: to retard the flow of heat, to reduce the amount of duct-transmitted sound, and/or to act as a vapor barrier. To retard the flow of heat, ducts may be insulated on the inside with duct liner, or on the outside with duct wrap. To reduce the amount of duct-transmitted sound, a product called sound liner may be used. As a vapor barrier, ducts are usually wrapped with a vapor sealable material such as foil or plastic.

Duct Insulation

 

Topic Summary

There are also different kinds of ductwork. For example, there are rigid ducts and flexible ducts. Within the category of rigid ducts are galvanized steel ducts, stainless steel ducts, fiberglass ducts, and fiberglass board ducts. Flexible ducts also come in different materials: canvas, cloth, lightweight aluminum (as in a dryer vent duct), or ducts formed of two concentric metal coil springs encapsulated with plastic or metalized foil (the space between the coils is filled with fiberglass insulation). See articles 23 30 00, 23 31 16.13, and others for further information on ductwork. Each type of duct may be used in multiple applications.

The type and amount of duct insulation is dictated by many factors, ranging from energy codes (Ashrae 90.1) to budget or financial constraints. There are some applications where no insulation is required or practical. A waste water treatment facility’s ducts are usually fabricated from high quality stainless steel or rigid cast fiberglass ducts. Insulation is not required because in this kind of application, the purpose of the ductwork is not comfort, but ventilation. There are also situations in commercial buildings where duct insulation is not required, for example, return ductwork in a plenum (although sound control liner may be installed to reduce noise, or insulation installed anyway to act as a vapor barrier). Exhaust ductwork for occupied spaces such as bathrooms does not generally require insulation. But if the exhaust is high temperature, insulation may be required for either fire protection or personal safety. The energy code defines what is required for occupied buildings. Other standards may also apply for industrial buildings.

There are different manufacturers of duct insulation, among which Johns-Manville, Knauf, and Owens Corning are probably the most well known.

When it comes to a building's comfort, one of the most important but least considered elements is its insulation. Remember that heat always flows from a hot substance to a colder one; this includes heat being lost through the surfaces of ductwork. Overall, the poorer the insulation and insulation installation, the more heat will have to be added to the inside of a space to maintain comfort. More heat added translates to higher energy costs and an increased amount of greenhouse gasses. Insulation can always be improved upon, but some additions of insulation are more costly than others. Duct insulation is one of the components in the overall system which can be easily improved, provided that the ducts are accessible.

Insulating heating ducts in the crawl space under the house can be done with a kind of bubble wrap that has foil on both sides. Check the fire rating on the insulation. This type of insulation is not installed in a commercial building but may be suitable for a private dwelling. The homeowner should check with a mechanical contractor or the mechanical code before installing this kind of product in a personal residence.

Last modified on Tue, Aug 24, 2010
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