There are other considerations when sizing an area for a/c , such as maximum heat load etc ......... but a 12,000 btu system should handle the job .

A 20 x 14 room is 280 square feet, not 600. (Assuming that 10 foot ceiling height.)

Even if you're on the top floor, with a southern exposure, a small air conditioner should do the job. Maybe 5,000 BTU; a bit larger if you've got a big screen TV or kick-a** gaming computer in the room.

If the space is really 600 square feet, not 280, something larger would be in order.

You need a bit larger one for your 600 sq ft room....

I have room that is 20x14x10, 600 sq ft. I want to heat/cool it with a through the wall split system. The room walls have R15 and the ceiling has R30 insulation. Can you tell me how many BTU system I need for this purpose? (Michigan)

Thank you