How much efficiency is really lost due to ductwork not being taped and insulated? I have the square kind that is thick, then breaks off as you go down the line to go to the individual vents. I only ask because my ductwork is really heating up the wall the thermostat is on. The house is 67 degrees, the thermostat will read 73, and the wall will be 78 degrees. Is this common? And how difficult would it be to just replace it all with that flexible ductwork stuff that comes insulated already?