Insulating Ductwork In Attic

Check the speed of the blower motor on the furnace.

Insulating ductwork in 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. 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. Most attic ducts are insulated flex ducts that is flex ducts with r 6 or r 8 fiberglass insulation along with an exterior polyethylene jacket. Let s use your existing duct board surface that now faces the attic as an example.

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. Because the attic is hot it warms the surface of the duct board above the dew point temperature of the air in the attic. The duct insulation should include a vapor barrier. Acute temperatures in these areas contribute to thermal loss in metal ductwork.

If you then put a layer of insulation over this surface this same surface will now begin to cool down. 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. Sometimes the insulation is inside the ductwork. Make sure the foil surface of the insulation is free of dust before applying the tape.

To insulate the exterior you have a choice between sleeve style insulation and blanket wraps which literally wrap around the 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. When insulating hvac ductwork use a foil faced fiberglass insulation with an r 6 or higher r value.

Because the simplest and cheapest way to insulate an attic is to add material to the floor. Use metal flex or fiber board ducts that are insulated to code. Mechanically fasten and mastic seal all duct connections. Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct.

Use a paintbrush to apply duct mastic to the joints where an elbow. Plan to pull up the flooring and layer new insulation on top of the old. 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. Flexible ductwork comes with different insulation r values.

Although both the attic floor and the ductwork are insulated ted recognizes the situation isn t ideal.