The 4th Generation MrCool DIY Multi-Zone 36k BTU 4 Zone Ductless Mini Split is an easy-to-install, efficient system that will keep your space comfortable. Its outdoor heat pump can cool in the summer and heat in the winter, with a high efficiency SEER rating of 21.5 thanks to the variable speed DC inverter. The three 9,000 BTU air handlers can handle rooms of 375-450 square feet, while the 12,000 BTU air handler can take on up to 600 square feet.