For a newly installed 90,000 BTU gas frunace and 2.5 ton AC, the furnace manual states there must be a minimum of 250 sq. inches of free air space in the upper portion of the furnace closet door and 6 inches between closet door and front of furnace.

My furnace closet is in the hallway. My furnace has two 16″x20″ return air grilles on the front of it with 2 filters of the same size.

I read online a lot of different opinions as to what the size of return air grille should be. Should I accept what the manual states or make a larger return grille opening in the closet door? My house is approximately 1,300 sq. ft. Not very well insulated. My old furnace was smaller and did not have AC.

Thanks.