How to Properly Cover Round Air Ducts with Insulation

The typical ductwork system is fabricated of square or round galvanized steel. Air ducts are most often located in areas without climate control, which leaves ducts susceptible to heat gain/loss in extreme basement and attic temperatures. Square ducts may be best insulated with rigid foam or fiber board. However, insulating round air ducts requires more patience and finesse. Here’s how the pros do it:

Duct Inspection and Preparation

An HVAC professional will inspect existing ducts for air leaks through loose connections, fallen ducts and holes. Heat gain/loss issues are addressed by inspecting insulation if any is installed. Notes are also taken for sagging, damaged and corroded duct sections. Following ACCA (Air Conditioning Contractors of America) Manual D guidelines, ducts are sealed, repaired and/or supported in preparation for insulation installation.

Insulating Round Air Ducts

Standard fiberglass insulation batts or rolls are practical for providing a sufficient barrier to heat gain/loss. The width of the top-and-bottom insulation batts/rolls are sized to the perimeter of the round ducts, and the vapor barrier (paper or foil) is faced out. For basement and crawlspace installations, twine may be stapled to the joists and taped to the top insulation portions with foil-backed tape to support the insulation. Support straps should be double-checked to prevent sagging and future leaks.

For insulating round ducts in the attic, the same basic procedures are followed. Your HVAC pro will make sure your ducts have plenty of space between building objects and materials to prevent knocking, banging and prevent damage to insulation. Insulation is installed beneath and on top of round ducts and secured with foil-backed tape. Special care is taken not to compress the insulation, which reduces insulation R-value (rating of resistance to heat loss). Attic insulation in our Northwest Arkansas area should be a minimum of R-49, with R-60 providing the best results.

To speak with an HVAC professional about insulating round air ducts in your Northwest Arkansas home, please contact Paschal Heat, Air & Geothermal for more information.

Our goal is to help educate our customers in Springdale, Arkansas about energy and home comfort issues (specific to HVAC systems). For more information about air ducts and other HVAC topics, download our free Home Comfort Resource guide.

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