Best Way To Insulate Attic Ductwork

When insulating hvac ductwork use a foil faced fiberglass insulation with an r 6 or higher r value.

Best way to insulate attic ductwork. Use a paintbrush to apply duct mastic to the joints where an elbow. Press a continuous strip of foil tape to all longitudinal seams along straight runs of duct. Use the type of metallic foil duct tape recommended by the insulation manufacturer to seal and hold the insulation in place. In humid climates burying ducts can be a risky strategy.

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. That s one of mike macfarland s jobs in northern california where burying ducts is a no brainer. Because the attic is hot it warms the surface of the duct board above the dew point temperature of the air in the attic. 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.

That s what happened to the ducts in the lead photo of this article. Bury the ducts deeply in insulation. Install loose fill insulation to cover the ducts and the attic floor to meet or exceed the code required r value for attic insulation. Test total duct leakage.

Add additional sealant if necessary. Let s use your existing duct board surface that now faces the attic as an example. Mechanically fasten and mastic seal all duct connections. If you then put a layer of insulation over this surface this same surface will now begin to cool down.

The duct insulation should include a vapor barrier cover. Plan to pull up the flooring and layer new insulation on top of the old. Because the simplest and cheapest way to insulate an attic is to add material to the floor. For an added layer of protection you can apply duct mastic to the tape and duct.

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. Check the speed of the blower motor on the furnace.