Here’s a photo I took a few months ago during an energy retrofit. Yup, that’s 110F supply air from the furnace being dumped into the unconditioned attic (for thermal purposes what we call “outdoors”). The most plausible explanation is that this was an attempt to fix a cold master bedroom a few feet away. To make matters worse, the duct was tapped into the very end of a supply trunk in the basement (the place where you’re never supposed to connect to).
A couple of points related to this:
1) I haven’t seen empirical evidence on the matter, but it seems like generally there’s an inverse relationship between having work performed on one’s house, and the performance of the house.
2) Successful strategies for remedying comfort issues should probably include thermal upgrades.
In this case disconnecting the duct at the trunk, removing the duct from the attic, adding 2″ polyiso to select areas of the bedroom walls and rafters, air-sealing, and insulating the entire attic resulted in big comfort improvement.