My upstairs sidewall air return duct continues past the register up to the attic (HVAC unit is on main floor). There is actually no duct installed in the wall, its just a duct formed by the framing and drywall.
Is this uncecessarily pulling hot air from the attic and taxing my A/C. Should the return be "boxed" in the wall so that only air from within the room is returned?
the return should only pull from the areas that are being conditioned by the discharges.it should be "ducted" from the wall mounted grill down to the unit on the main floor....any extra loads will raise the return and in the resulting discharge (18F) evap split cause the unit to see a load returning that it wasn't designed for and cause the unit to run longer.