Insulating Ductwork In Attic

Sometimes the insulation is inside the ductwork.

Insulating ductwork in attic.

Acute temperatures in these areas contribute to thermal loss in metal ductwork. A metal duct conveying cool conditioned air through a broiling attic in summer or warm air through a chilly crawl. The duct insulation should include a vapor barrier. Because the moving air is in the ductwork for only a short period of time it does not need the insulation r value the attic floor requires.

To insulate the exterior you have a choice between sleeve style insulation and blanket wraps which literally wrap around the ductwork. To install sleeves you must either disassemble the ductwork and slide it on before reassembling the ducts or as many homeowners find themselves doing slit it and wrap it around like the blanket style material. Because the attic is hot it warms the surface of the duct board above the dew point temperature of the air in the attic. Flexible ductwork comes with different insulation r values.

Make sure the foil surface of the insulation is free of dust before applying the tape. Summer hasn t even arrived he notes in a post at gba s q a forum and when the temperature outside climbs to more than 95 f the temperature in the attic tops 120 f. Mechanically fasten and mastic seal all duct connections. Other times insulation may be on the outside.

If you then put a layer of insulation over this surface this same surface will now begin to cool down. Scope install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords. Check the speed of the blower motor on the furnace. Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct.

If necessary switch the wires to reduce the blower to its lowest. Although both the attic floor and the ductwork are insulated ted recognizes the situation isn t ideal. But if the floor is covered in plywood you can t stuff enough insulation beneath it to do the job sufficiently not even in warm climates. Let s use your existing duct board surface that now faces the attic as an example.

Use a paintbrush to apply duct mastic to the joints where an elbow. Because the simplest and cheapest way to insulate an attic is to add material to the floor. When insulating hvac ductwork use a foil faced fiberglass insulation with an r 6 or higher r value. Use the type of metallic foil duct tape recommended by the insulation manufacturer to seal and hold the insulation in place.

When these ducts are exposed to exterior air the plastic jacket never gets cold enough to permit condensation because the hot attic air keeps the plastic jacket warm.