I have a finished 3rd floor room in my 1925 brick home, there is a uninsulatted attic above this room and the house has a slate roof. I have central air with a separate duct from the a/c and gas forced air unit that is in the basement, this room is boiling in the summer and freezing in the winter. I am in the need for a new furnace for the whole house, the a/c is new,would zoning the new unit help? ( would the compressor unit outside run constantly)? I don't want to use portable window unit. Any help would be appriciated. Thank you