Mini Split Size Calculator

For cooling, 12,000 BTU: the ENERGY STAR chart covers 450 to 550 sq ft with 12,000. If the mini-split is your main heat in a cold climate, size for heat instead. An average 500 sq ft room in zone 5 loses about 11,900 BTU an hour at 2 F, which takes an 18,000 BTU class hyper-heat unit.

About 20 BTU per sq ft for cooling a typical room, from the ENERGY STAR room chart (9,000 BTU for 400 sq ft, 18,000 for 1,000). Small rooms run higher per sq ft and big open areas lower. Heat loss varies far more: about 6 BTU per sq ft for a tight house in Miami up to over 40 for a drafty one in northern Minnesota on the coldest night.

Neither, but a little over is safer. Inverter units throttle down to about a third of their size, so they handle some oversizing better than window units. A head much bigger than the room still short-cycles and dehumidifies poorly; we cap the match at 50% over the load, with 9,000 BTU as the smallest common head.

One room: single-zone. Several rooms: a multi-zone puts every head on one outdoor unit and one circuit. Separate single-zone units cost more wall space but each runs at its own best efficiency, a failure only takes out one room, and small ones run on 115V or install DIY. The tool prices both.

Yes, if it is sized for heat and rated for your cold. ENERGY STAR's cold-climate heat pumps must still deliver 70% of their rated heat at 5 F. Hyper-heat models are rated to keep heating at -13 F or -22 F. Standard units often stop being rated at 5 F or -4 F, so in zones 5 to 7 keep a backup or buy hyper-heat.

115V units top out at 12,000 BTU in what we list and still need their own circuit (the Senville LETO 12,000 calls for a 20 A breaker). Anything 15,000 BTU and up, every hyper-heat unit we list and every multi-zone system runs on 230V from a 2-pole breaker.

Only a pre-charged Quick Connect system like MRCOOL DIY is built for it: the lines snap together with no vacuum pump. Every other system needs its lines vacuumed and opened by a tech certified under EPA Section 608, and makers like Cooper & Hunter and Senville say professional installation is required. The electrical circuit may need a permit either way.

Each model has a limit. Senville LETO and DELLA Serena units are charged for up to 25 ft, Pioneer's 2- and 3-zone kits for 50 and 75 ft of total line. Past that, the installer adds refrigerant. DIY Select lines are a fixed 11.5 ft and must not be cut.