As a Midwesterner, it is absolutely bonkers to me how common it appears to be for HVAC systems to get installed in attics.
Don't do that. Stop doing that! WTF?
That's bad enough, but then you go and run the ducts up there, too?
Y'all.
If you keep the system and the ducts within the space you're trying to heat and cool, you don't have to account for any losses, now, do ya?
Put the air handler in a utility closet. Run ducts /below/ the ceiling. Enclose with soffiting if you must.
The end.
@TechConnectify
If you think that's bad, at some point builders in North Texas decided that water heaters up there were a good idea, too, combined with ventilation that couldn't be closed. In February of 2021, a lot of people learned the hard way why that was a terrible idea.
@Eastcheap *facepalm*
I say this with 100% sincerity (and a hint of pride): If you want to learn how to build a climate-resilient home, just come up here. We've been doing it since forever because we have to.
@Eastcheap And, unironically, it's a big reason I'm staying put.
My home can handle 100°F weather with stupid humidity just as well as it can handle -20° weather because that's just what happens.
We cannot take design shortcuts, and we don't.