Answer 1: We need to consider a few things first. What size BTU Needed-. 0-300 Sq Feet a 9000 btu would be best for you. 300-500 Sq Feet a 12000 Btu 1 Ton Mini Ductless Split Air Conditioner would be best for you. 500-800 Sq Feet a 18000 Btu 1.5 Ton Mini Ductless Split Air Conditioner.