Free Mini-Split Sizing Calculator
Estimate a preliminary mini-split room load for a bedroom, office, ADU or converted garage in Sacramento and Placer. Free BTU calculator with local references.
How to use this estimate
This simplified model combines assumed heat transfer through walls, windows, roof and floor with air exchange, sunlight, people and equipment. Your home's measured condition can produce a substantially different result.
See the method, assumptions and source references
Full calculation assumptions appear with your result.
Local weather references: CEC 2025 Joint Appendix JA2, Table 2-3. Cooling uses 1% dry-bulb; heating uses 0.6% dry-bulb. Nearby references are identified explicitly. These are planning weather values, not a property-specific climate-zone determination.
Final professional work: ACCA Manual J loads, equipment selection and Manual D duct design. This tool is not ACCA-approved software or a permit compliance calculation.
What size mini-split do I need for my room?
A mini-split should be selected for the room's heating and cooling load and the equipment's operating range. Start with the space's floor area, ceiling height, exterior walls, windows, insulation and sun exposure. A small room can need much less capacity than an ADU or converted garage with the same floor area.
This free mini-split sizing calculator explores one space at a time. It can help you prepare for a bedroom, home office, studio or garage-conversion assessment in the Sacramento and Placer region. Conditioned rooms above or below can reduce exposed building area; a detached space may have more exterior walls and roof exposure.
Is a 12,000 BTU mini-split always right for a small room?
No. Nominal capacity is only one selection factor. A unit whose minimum output is too high for a small room may have difficulty matching a light load. Check the matched indoor/outdoor equipment's minimum and maximum output, distribution and heating performance with your installer.
Can I add room results to size a multi-zone outdoor unit?
Do not simply add the rounded estimates and select an outdoor unit. A multi-zone design requires individual room loads, simultaneous demand, approved indoor/outdoor combinations, capacity allocation and manufacturer correction factors. Heco can assess the full layout.
What about garages, ADUs and open doorways?
Insulation, roof exposure and connections to other spaces can change the load substantially. An unfinished garage should not be treated as an insulated bedroom. This calculator does not determine whether a space is permitted for occupancy or whether electrical or construction upgrades are required.
Does colder foothill weather change mini-split selection?
Yes. Heating capacity varies with outdoor temperature and equipment model. The tool identifies its weather reference, including a nearby station when used. Elevation and actual property conditions need confirmation before equipment selection.
Published by Heco Heating and Air Conditioning • California C-20 contractor license #1050351. Tools are for preliminary planning; contact Heco to verify property conditions and service availability.