What size mini-split do I need for 300 square feet?

About 9,000 BTU. In a mixed climate like Atlanta the estimate is 9,000 BTU (cooling load 8,000 BTU/h, heating load 5,700 BTU/h). Hot climates need more cooling capacity and cold climates more heating capacity, as the table shows.

How many BTU do I need for 300 square feet?

For cooling, roughly 8,700 BTU/h in a hot, dry climate and 6,900 BTU/h in a cold one. For heating, from 4,500 to 9,000 BTU/h depending on how cold winters get. Older, drafty homes need up to 30% more.

Is it better to oversize or undersize a heat pump?

Neither, but slight undersizing is usually less harmful for cooling. An oversized unit short-cycles and leaves the air clammy. In cold climates, size for the heating load and check the unit’s output at 5°F, or plan for backup heat on the coldest nights.

What size mini-split for 300 sq ft?

Short answer: 9,000 BTU, depending on your climate and insulation. In a mixed climate like Atlanta: 9,000 BTU.

By climate

Hot and dry (Phoenix)9,000 BTU
Hot and humid (Houston)9,000 BTU
Mixed (Atlanta)9,000 BTU
Cold (Chicago)9,000 BTU
Very cold (Minneapolis)9,000 BTU

Average insulation, 8 ft ceilings, three occupants.

Best 9,000 BTU mini-splits

Most efficient

Carrier 37MPRAQ09AA3

9,000 BTU mini-split · 45M Series · cold-climate certified

SEER2: 33.5
HSPF2: 14.6
Heat at 5°F: 13,500

Top-rated certified model in the size most 300 sq ft rooms need.

Full specs and running cost

Best for cold winters

York YRACGJ09WHAA

9,000 BTU mini-split · Y600 · cold-climate certified

SEER2: 23.0
HSPF2: 11.4
COP at 5°F: 2.57

Cold-climate certified, best efficiency at 5°F in this size.

Full specs and running cost

Compare all 9,000 BTU mini-splits

Work it out for your room

Pre-filled with 300 sq ft. Pick your city and adjust insulation, sun and ceiling height.

Your space

Area to heat and cool sq ftCeiling heightInsulationSun exposurePeople who usually use itIncludes the kitchen?

Your climate

StateCity

Mini-split size: 9,000 BTU
Central / ducted size: 1.5 ton
Cooling load: 8,700 BTU/h
Heating load: 4,500 BTU/h

See 9,000 BTU mini-splits See 1.5-ton central heat pumps

Rule-of-thumb estimate: cooling follows the ENERGY STAR room sizing table, heating uses typical BTU per square foot for the climate (NOAA 1991-2020 heating degree days). For a whole-house system, ask your installer for a Manual J load calculation.

More detail

Cooling and heating loads by climateBTU/h

Hot and dry (Phoenix)cooling 8,700 · heating 4,500
Hot and humid (Houston)cooling 8,700 · heating 4,500
Mixed (Atlanta)cooling 8,000 · heating 5,700
Cold (Chicago)cooling 7,600 · heating 8,100
Very cold (Minneapolis)cooling 6,900 · heating 9,000

Cooling follows the ENERGY STAR sizing table; heating uses BTU per sq ft for the climate (NOAA 1991-2020 normals).

How insulation changes the sizein Atlanta

Poor9,000 BTU · heating 7,400 BTU/h
Average9,000 BTU · heating 5,700 BTU/h
Good9,000 BTU · heating 4,600 BTU/h
Very good9,000 BTU · heating 3,700 BTU/h

Top 5 9,000 BTU mini-splitsranked by SEER2

#	Model	SEER2	EER2	HSPF2	COP at 5°F
1	Carrier 37MPRAQ09AA3	33.5	17.0	14.6	2.00
2	MDV MOX430-09HFN10-M1H	33.5	17.0	14.6	2.00
3	Fujitsu AOUH09KTAP1	33.5	19.1	14.0	2.48
4	Mainline ML09HP230CALH-Oalso sold as 2 other model numbers	33.3	17.0	14.6	2.00
5	Midea MO1SS-H09B-2Aalso sold as 10 other model numbers	33.3	17.0	14.6	2.00

Questions3

What size mini-split do I need for 300 square feet?: About 9,000 BTU. In a mixed climate like Atlanta the estimate is 9,000 BTU (cooling load 8,000 BTU/h, heating load 5,700 BTU/h). Hot climates need more cooling capacity and cold climates more heating capacity, as the table shows.
How many BTU do I need for 300 square feet?: For cooling, roughly 8,700 BTU/h in a hot, dry climate and 6,900 BTU/h in a cold one. For heating, from 4,500 to 9,000 BTU/h depending on how cold winters get. Older, drafty homes need up to 30% more.
Is it better to oversize or undersize a heat pump?: Neither, but slight undersizing is usually less harmful for cooling. An oversized unit short-cycles and leaves the air clammy. In cold climates, size for the heating load and check the unit’s output at 5°F, or plan for backup heat on the coldest nights.

Other sizes

All sizing guides