Cheapest Mini Split

Mini split sizing calculator

Size the system before you compare prices. Buying a size up because it is cheaper per BTU is the most common and most expensive mistake in this category: an oversized unit cools the air before it has pulled the humidity out, then short-cycles, leaving the room cold and clammy and wearing the compressor faster.

The five sizes sold as DIY, drawn as rooms to the same scale — area is BTU ÷ 20, the rule the calculator starts from — each with the cheapest live single-zone price at that size today. The room the calculator picks is filled in.

9,000 BTU450 sq ftfrom $58012,000 BTU600 sq ftfrom $55018,000 BTU900 sq ftfrom $80024,000 BTU1,200 sq ftfrom $69036,000 BTU1,800 sq ftfrom $2,500

Size decides the voltage too: above 12,000 BTU every system here needs a 230 V circuit — what is sold at each voltage.

01

What this actually calculates

It starts from the widely used approximation of 20 BTU per square foot, scales it for ceiling height (because you are cooling a volume, not a floor), then applies multipliers for sun exposure and insulation, adds 600 BTU for each occupant beyond the first two, and adds 4,000 BTU if it is a kitchen. Those adjustments are the standard ones published by ACCA and repeated across the trade; the arithmetic is shown above the result rather than hidden behind a button, so you can check it.

02

What it is not

It is not a Manual J load calculation, and it should not be treated as one. A real load calculation accounts for window area and glazing type by orientation, wall and roof assemblies, infiltration rate measured or estimated, duct losses, climate design temperatures for your specific location, and internal gains from appliances and lighting. Two rooms with identical floor area in the same house can differ by 50% once those are counted. If you are heating as well as cooling, or you are anywhere with a real winter, the heating load usually sets the size and this calculator does not model it at all.

Use this to get into the right size bracket and to sanity-check a quote. If it lands you between two sizes, take the smaller one: undersizing costs you a few degrees on the worst afternoon of the year, while oversizing costs you comfort and compressor life every single day.

03

Then compare price per BTU inside that size

Once the size is settled, the ranking that matters is the one within it. Larger systems are somewhat cheaper per BTU, but the effect is weak in this catalogue (r = -0.20), not the rule of thumb the trade repeats. The clear exception is the smallest size: 9,000 BTU systems start at $64.44 per 1,000 BTU, because the compressor, inverter board and shipping crate cost much the same whatever the output. What actually moves the number is which system you pick within a size: at 24,000 BTU the range runs from $28.75 to $154.17 per 1,000 BTU, a factor of 5.4, and that gap is larger than anything between the sizes. Pick the size, then open that size’s page: