I have a duplex and one furnace crapped out likely because it had the return in the basement. It’s upstate NY, so it gets cold.
If I want it done 100% right. I need ducts run all the way to the top level for my return air. That would be very expensive and disruptive since there are tenants.
Another option is to to have another return installed to the 1st level unit. Note there is no central AC only heat.
Can I go with this option to install the return on the first floor even though it’s for the upper unit?