calcs.homes
calcs.homes
Enter the room you want to condition and this mini split sizing calculator estimates the cooling load and points you to the nearest standard ductless head size.
Estimate only — an oversized mini-split short-cycles and dehumidifies poorly; size to the load, not above it.
We estimate the room's cooling load the same way as a room AC — area times a climate factor, adjusted for ceiling height and sun — then snap it to the nearest standard ductless head: 9,000, 12,000, 18,000, 24,000, 36,000, or 48,000 BTU. Those sizes correspond to roughly 0.75, 1, 1.5, 2, 3, and 4 tons.
With mini-splits it is better to land slightly under the calculated load than over it. They modulate down well but not up, and an oversized head in a single room will cool the air quickly, throttle back to minimum, and leave the space humid. If the load falls right between two sizes, choose the smaller one unless the room has heavy afternoon glass.
Usually a 9,000 or 12,000 BTU head, depending on climate, ceiling height, and sun. 12,000 BTU (one ton) is a common choice for an average 400 sq ft room.
For heating in a cold climate, choose a cold-climate model rated to hold capacity at low temperature rather than jumping to a bigger head — oversizing hurts summer dehumidification.
Yes, a multi-zone condenser feeds two to five heads. Size each head to its room, then confirm the combined total is within the outdoor unit's rated capacity.