>>106322945
Most often the duct work is in the attic as you say (occasionally the garage). Taking that into account, the parasitic loss is between 10%-30%. Close to the lower end the shorter and better insulated the run is. I'm not shitting on HVAC at all and I was surprised at the numbers but it makes sense. Any number of ducts in itself is going to lower efficiency. It's of course possible that an HVAC could still be overall more efficient and I assumed that was the case. However, over the door ductless systems and made to a high efficiency standard with properly sized coils and inverter compressors that run at variable speeds (same for the U-style window units just not quite as good though close). It all adds up to higher efficiency than HVAC. Still shitty for an entire house since obviously you're only outputting air to one room but the problem isn't efficiency, it's comfort