HVAC Extension

Basement & Attic Conversions

HVAC Extension and Ductwork for Comfortable Year-Round Use

Basements and attics are the two most thermally challenging spaces to condition in a Michigan home. Before extending any existing system, we run a Manual J load calculation for the new space and verify the existing equipment has the spare output capacity to serve it. A furnace already running at 90 percent of its rated output doesn't have capacity for 800 more square feet. Extending ductwork from an undersized system makes every room worse, not just the new one.

For basements, trunk line extensions drop from the existing first-floor duct system through a new opening, with branch ducts running to supply registers positioned for even distribution. Return air is as important as supply — a basement with supply registers and no return path back to the air handler creates pressure imbalance that affects the whole house. We size return grilles for adequate free area relative to the supply volume.

Attics present a longer duct run and higher summer heat gain than any other zone in the house. Proper insulation at the roof assembly reduces that load substantially. After accounting for insulation, we size the duct extension or supplemental mini-split for the remaining cooling load. Mini-splits are often the practical choice for attic zones — they're easier to install without disrupting existing ductwork and provide individual zone control that a central system can't match.