The answer is virtually anywhere. SpacePak has small ducts and is flexible tubing to distribute the air instead of bulky sheet metal ductwork.
This tubing is seamless, and saves on energy unlike leaks found in sheet metal. SpacePak is flexible, so passages have no corners to accumulate dust, pollen, or mold. The tubing’s narrow diameter allows it to be placed in the spaces behind walls, floors, and ceilings: it can be installed with virtually no disruption to livable space, nor to interior architectural features.