Insulating Ductwork In Attic

Flexible ductwork comes with different insulation r values.

Insulating ductwork in attic.

Scope install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords. 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. The duct insulation should include a vapor barrier. Plan to pull up the flooring and layer new insulation on top of the old.

Make sure the foil surface of the insulation is free of dust before applying the tape. Mechanically fasten and mastic seal all duct connections. Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct. To insulate the exterior you have a choice between sleeve style insulation and blanket wraps which literally wrap around the ductwork.

Use the type of metallic foil duct tape recommended by the insulation manufacturer to seal and hold the insulation in place. If necessary switch the wires to reduce the blower to its lowest. 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. 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.

Let s use your existing duct board surface that now faces the attic as an example. Use metal flex or fiber board ducts that are insulated to code. If you then put a layer of insulation over this surface this same surface will now begin to cool down. Although both the attic floor and the ductwork are insulated ted recognizes the situation isn t ideal.

Sometimes the insulation is inside the ductwork. 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. 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. Other times insulation may be on the outside. Because the attic is hot it warms the surface of the duct board above the dew point temperature of the air in the attic. 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.

Check the speed of the blower motor on the furnace.