Best Way To Insulate Attic Ductwork

Bury the ducts deeply in insulation.

Best way to insulate attic ductwork.

Air sealing all the ducts and air handler connections and seams and air sealing all the duct boots to the ceiling gypsum and any other penetrations is a critical first step prior to adding any insulation. If you then put a layer of insulation over this surface this same surface will now begin to cool down. Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct. Let s use your existing duct board surface that now faces the attic as an example.

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 best way to do buried ducts unless you live somewhere where you have to worry about ice dams is to close up the soffit vents and replace the ridge vent with a diffusion vent i see prescriptive practices regarding diffusion venting have been addressed in the irc 2018 at least for us climate zone s1 2 3. 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 simplest and cheapest way to insulate an attic is to add material to the floor.

In humid climates burying ducts can be a risky strategy. Install loose fill insulation to cover the ducts and the attic floor to meet or exceed the code required r value for attic insulation. For an added layer of protection you can apply duct mastic to the tape and duct. That s one of mike macfarland s jobs in northern california where burying ducts is a no brainer.

Check the speed of the blower motor on the furnace. When insulating hvac ductwork use a foil faced fiberglass insulation with an r 6 or higher r value. 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.

Add additional sealant if necessary. Use a paintbrush to apply duct mastic to the joints where an elbow. Mechanically fasten and mastic seal all duct connections. That s what happened to the ducts in the lead photo of this article.

To insulate the exterior you have a choice between sleeve style insulation and blanket wraps which literally wrap around the ductwork. Test total duct leakage.