Mini-Split Sizing Calculator

Insulation Quality applies a multiplier to the whole base load: poor insulation (level 1) multiplies it by 1.3, average (level 2) leaves it unchanged, and good insulation (level 3) cuts it by 15% (factor 0.85). Moving from poor to good insulation on an otherwise identical room lowers the required BTU by roughly a third, which is why the two ends of this 1-3 scale matter more than they might look like they should from a single-step slider move.

No. Typical SEER Rating is hardcoded at 20 in the calculator — it represents a middle-of-the-road efficiency for modern mini-splits (which commonly range 18-30 SEER) and is used only to back into the Est. Annual Cooling Cost estimate. It does not change based on any input you enter, and it is not read from a real unit's spec sheet, so treat the annual cost figure as a loose approximation, not a quote for a specific model.

The calculator only scales load for ceilings taller than 8 ft — a room at exactly 8 ft gets no adjustment, while a 9 ft ceiling multiplies the base load by 9/8 (12.5% more). Below 8 ft the input is accepted but has no extra effect, since the formula only checks whether height exceeds the 8 ft baseline, not how far below it a room sits.

Climate Zone is a 1-5 severity code, not a temperature: 1 is mild/coastal (0.8x load), 2 is moderate (0.9x), 3 is average (1.0x, the default), 4 is cold (1.1x), and 5 is very cold (1.25x). Like Insulation Quality, the steps between codes are uneven, and they get bigger toward the cold end rather than smaller: the swing from zone 4 to 5 (0.15x, the largest jump on the scale) is actually bigger in absolute terms than the swing from zone 1 to 2 (0.1x), even though both are one-step changes.