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What Size Mini Split for 300 Sq Ft?

Short answer: ≈8,000 BTU/h → buy the 9,000 BTU class at standard conditions (8 ft ceilings, average sun and insulation, DOE zone 4, two occupants), read straight off the ENERGY STAR chart. verified 2026-06-10 Adjust below for your real room.

Your room

Pre-set to 300 sq ft — change anything and the answer updates instantly.

Which zone am I in?
  • Zone 1: South Florida, Hawaii, Puerto Rico
  • Zone 2: Most of Florida, south Texas, southern Louisiana, Phoenix area
  • Zone 3: Most of the Southeast, central Texas, southern California
  • Zone 4: Virginia, Kentucky, Missouri, Kansas, coastal Oregon/Washington
  • Zone 5: Pennsylvania, Ohio, Illinois, Iowa, Colorado, southern New England
  • Zone 6: Minnesota, Wisconsin, Montana, Vermont, New Hampshire, most of Maine
  • Zone 7: North Dakota, northern Minnesota, high Rockies
  • Zone 8: Interior and northern Alaska

State examples are approximate — zones are assigned by county. Use the DOE lookup for your county. DOE county lookup ↗

300 sq ft by climate zone

DOE / IECC zoneAdjusted estimateBuy class
Zone 1 South Florida, Hawaii, Puerto Rico9,200 BTU12,000 BTU class
Zone 2 Most of Florida, south Texas, southern Louisiana, Phoenix area8,800 BTU9,000 BTU class
Zone 3 Most of the Southeast, central Texas, southern California8,400 BTU9,000 BTU class
Zone 4 Virginia, Kentucky, Missouri, Kansas, coastal Oregon/Washington8,000 BTU9,000 BTU class
Zone 5 Pennsylvania, Ohio, Illinois, Iowa, Colorado, southern New England8,000 BTU9,000 BTU class
Zone 6 Minnesota, Wisconsin, Montana, Vermont, New Hampshire, most of Maine8,000 BTU9,000 BTU class
Zone 7 North Dakota, northern Minnesota, high Rockies8,000 BTU9,000 BTU class
Zone 8 Interior and northern Alaska8,000 BTU9,000 BTU class

Zone multipliers are editorial rules of thumb (cooling-season length/intensity); zone definitions per the DOE IECC climate-zone map. In zones 5+ heating, not cooling, usually decides the size — see methodology.

What moves the number

  • Very sunny room: +10% (ENERGY STAR) → 8,800 BTU → 9,000 class
  • 10 ft ceilings: +25% air volume (rule of thumb) → 10,000 BTU → 12,000 class
  • Kitchen: +4,000 BTU (ENERGY STAR) → 12,000 BTU → 12,000 class

Verified 9,000 BTU models for 300 sq ft

Single-zone mini-split models in the 9,000 BTU class — every spec sourced and dated.
ModelBTUSEER2HSPF2VoltMin tempInstallVerified priceSource
Pioneer Quantum Ultra (WYT-24)
WYT009ALSI24RL-10S		 9,000 23 9.5 115V -13°F Pro $1,083 sale / $1,549 list (pioneerminisplit.com, Jun 2026) spec ↗
Senville LETO
SENL-09CD		 9,000 21.5 — 115V 5°F Pro $699.99 (senville.com, Jun 2026) spec ↗

— = not published by the manufacturer (we never guess)Specs verified against each linked source on 2026-06-10Prices move — treat as bands, not quotes

More on what a 9,000 BTU unit covers →

FAQ

What size mini split do I need for 300 sq ft?

Baseline answer: about 8,000 BTU/h of cooling per the ENERGY STAR chart, which means buying a 9,000 BTU class unit. Sun, ceiling height, insulation and climate zone move the number — use the calculator above with your real inputs.

Will a smaller unit work in 300 sq ft?

If the room is heavily shaded, ENERGY STAR says reduce capacity ~10% (≈7,200 BTU here), which usually keeps you in the same size class. Undersizing beyond that means the unit runs flat-out and may not hold temperature on peak days.

What about heating 300 sq ft in a cold climate?

Heat pump output falls as outdoor temperature drops. If this unit is your primary winter heat in DOE zones 5+, size up one class and pick a model rated for low ambients (−13°F or below; the Senville AURA in this dataset is rated to −22°F). Confirm with a Manual J calculation.

Estimate only — not a Manual J load calculation and not professional advice. Confirm with a licensed installer. Methodology & sources.