To save energy and reduce the unit size of your air conditioner, consider the following six ways for bringing air ducts inside: 1) simply movie them in and leave them exposed. 2) Condition the attic by moving the building enclosure to the roofline. 3) Carefully place the ducts in a lowered ceiling or soffit in the home. 4) If space is available, ducts may be installed between conditioned floors in a multi-story house. 5) Using a special scissor truss, ducts may be placed in the attic, below the building enclosure. 6) Encapsulated crawl space installation is also an option.
Read the full article here: How to Get Your Ducts Inside the Building Enclosure