We don't know the full story of the economics of conservation measures in basement houses because no comprehensive field studies have investigated their economic viability. Zones and basement homes. The energy conservation and safety questions surrounding basement forced air systems are as complex as the systems themselves. This Maryland basement is festooned with testing cables used to determine duct efficiency. Note that all of the visible ducts are uninsulated.
Ducts lose energy to the basement both when the air handler fan is on and when it is off.
Hypothetically consider an uninsulated sheet metal duct system at 95deg. F at waist level and 70deg. F at the joists. The energy will flow from this duct system at rates of 12,000 Btu per hour by convection and radiation and 7,000 Btu per hour because of leakage. Twenty-four percent of the furnace's energy will flow to the basement.