You shouldn’t install ducts in a vented unconditioned attic. As most GBAGreenBuildingAdvisor.com readers know, ducts belong inside a home’s thermal envelope, not in an environment that’s cold in the winter and hot in the summer.
Efforts by energy-efficiency experts to convince builders to move their ducts indoors haven’t been particularly successful. In states where slab-on-grade homes are common — in other words, in states where basements are rare — most builders still install ducts in vented unconditioned attics.
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