“The air temperature issuing from the registers plays a large part in providing for the occupants’ comfort level. If the air temperature is barely above body temperature, a person seated next to the register might experience a chilly draft. Yet this is exactly what can happen when duct runs are long and the register is far away from the furnace.”
The results and impact of temperature drop are outlined in chapter 21 of The Quiet Indoor Revolution, a book by Seichi Konzo and Marylee MacDonald, published by the Small Homes Council-Building Research Council, University of Illinois.