Venting a portable AC Unit through a roof termination instead of window
Hello,
I'm considering a portable A/C for a finished attic office with no window. The unit would sit directly below a sloped roof. Instead of using the supplied window panel, I'm considering having a professional install a full-diameter, weatherproof roof termination directly above the unit.
The OEM exhaust hose would remain approximately 3–5 feet long, would not be extended or reduced in diameter, and would rise gently at less than ~45° with minimal bends.
Manufacturers I've contacted (Frigidaire, LG, Whynter) only document window installations (Whynter also documents a modified wall installation), so none will officially approve a roof termination.
From an HVAC/airflow standpoint, is there a technical reason a properly sized, low-static-pressure roof termination wouldn't work? I'm particularly concerned about exhaust backpressure, condensation/rain management, and whether the upward slope presents a problem.
I'm not planning to DIY the roof penetration. I'm trying to determine whether the concept is sound before getting an HVAC/roofing contractor involved and am looking for some opinions at this point.
Thanks!