Mini split sizing chart: BTU by square footage, verified
30-second answer
This mini split sizing chart gives a heating load at 5°F and a cooling load for every common room size from 200 to 1,200 ft². A 600 ft² room in climate zone 5 with average insulation needs about 17,500 BTU of heat at 5°F and 13,500 BTU of cooling, which is an 18,000 BTU class unit. Read the heating column first if the unit has to carry winter. A chart value is a load, not a unit size: match it to a model’s verified capacity at 5°F, which is often far below the number on the box. Insulation, ceiling height, climate zone, and sun move every row. Above 1,400 ft², the chart stops and a Manual J load calculation takes over.
What size mini split do I need by square footage?
The chart below is our screening method run at one fixed set of inputs: climate zone 5, 8 ft ceilings, average insulation, average sun exposure. The cooling column starts from ENERGY STAR’s published room-size table[1]. The ceiling, insulation, and climate adjustments, and the whole heating model, are MiniSplitsHQ editorial factors, listed on the methodology page and not a published standard. Every figure here is reproducible in the mini split BTU calculator with those inputs.
| Room sizeft² | Heat needed at 5°FBTU/h | Cooling loadBTU/h | Cooling size classBTU |
|---|---|---|---|
| 200 | 6,000 | 5,500 | 6,000 |
| 300 | 8,500 | 7,500 | 9,000 |
| 400 | 11,500 | 9,500 | 12,000 |
| 500 | 14,500 | 11,500 | 12,000 |
| 600 | 17,500 | 13,500 | 18,000 |
| 800 | 23,000 | 17,000 | 18,000 |
| 1,000 | 29,000 | 20,000 | 24,000 |
| 1,200 | 34,500 | 22,000 | 24,000 |
| 1,500 | Manual J | Manual J | Multi-zone |
| All figures verified Aug 2026 · How we verify | |||
Three things to know before you read a row as your answer.
- The heat column is a load. It is the heat the room needs on a 5°F night. It is not a unit size, and no size class is attached to it. The section on 0°F weather below explains why.
- The cooling class rounds up. Mini-splits come in fixed sizes, so a cooling load always rounds up to the next real class, never down. A 500 ft² room screens at 11,500 BTU and lands in the 12,000 BTU class.
- The 1,500 ft² row is a stop sign, not a gap. Our method declines to publish a number above 1,400 ft² or 36,000 BTU. At that scale, a Manual J load calculation and usually a multi-zone layout replace any chart.
One chart is incomplete on purpose. The same 600 ft² room needs a different heat figure depending on insulation:
- With average insulation, the room needs 17,500 BTU of heat.
- With poor insulation, it reads 22,500 BTU.
- With 2015-or-newer code insulation, it reads 14,500 BTU.
That spread is the reason the what size mini split do I need hub sizes by load factors, not by square footage alone. This chart is the fixed reference those factors adjust.
Sanity check my setup: what moves a chart row?
Insulation moves a chart row more than any other single input. In our method, insulation spans a factor of 0.85 for 2015-or-newer code construction to 1.3 for little or none. Ceiling height, climate zone, and sun exposure stack on top of it. The factors multiply, which is why a tall, poorly insulated space outgrows its square-footage class so fast.
| Room sizeft² | Good (2015+ code)BTU/h | AverageBTU/h | Poor (little or none)BTU/h |
|---|---|---|---|
| 200 | 5,000 | 6,000 | 7,500 |
| 400 | 10,000 | 11,500 | 15,000 |
| 600 | 14,500 | 17,500 | 22,500 |
| 800 | 19,500 | 23,000 | 30,000 |
| 1,000 | 24,500 | 29,000 | Manual J |
| All figures verified Aug 2026 · How we verify | |||
A poorly insulated 1,000 ft² space pushes the heating load past 36,000 BTU in our method, so the chart stops and defers. Fixing the insulation is usually cheaper than the next size class up, and it attacks the load itself.
- Ceiling height scales the air volume. A 9 ft ceiling adds 6%, 10 ft adds 12%, and 12 ft or more adds 25% over the 8 ft baseline.
- Climate zone pulls heating and cooling in opposite directions. A 600 ft² room in zone 1-2 screens at 8,500 BTU of heat and 16,000 BTU of cooling. The same room in zone 6-7 screens at 20,000 BTU of heat and 12,500 BTU of cooling.
- Sun exposure is the one modifier with a published basis. ENERGY STAR says to cut capacity by 10% for a heavily shaded room and add 10% for a very sunny one[1]. It applies to cooling only.
Every factor is a field in the sizing calculator. If your room differs from its chart row in more than one way, run your real inputs instead of adjusting by feel.
Will it keep up when it’s 0°F outside?
A chart load and a unit rating are measured at different temperatures, and that gap is where winter sizing goes wrong. The Senville LETO 12k is rated 12,000 BTU of heating[2]. Its cold-climate directory entry lists a maximum of 6,600 BTU at 5°F, about half the rated figure[3].
Rated heating is measured at 47°F outdoors. The chart row is what the room needs at 5°F.
So a 400 ft² room that needs 11,500 BTU at 5°F is not covered by that 12,000 BTU unit on a 5°F night. It is covered by 6,600 BTU.
Cold-climate models hold far more of their rating. The MRCOOL DIY 5th Gen 18k lists 12,800 BTU of maximum heating at 5°F against an 18,000 BTU rating[3]. The hub’s verified 5°F numbers show the full spread across four models.
The buyer-side step is a comparison, not a calculation. Take the heat figure from your chart row to a specific model’s published capacity at 5°F, never to its nameplate. We deliberately attach no size class to the heating column, because capacity retention at 5°F varies too much between real units for one factor to be honest.
What size mini split for 1,500 sq ft?
Above 1,400 ft² we do not publish a chart value, and our calculator declines to give one. Manual J is the ACCA standard for residential load calculation, and at that scale it is the only honest tool[4]. Duct losses, room-to-room balance, and zone layout dominate the math past that point, and none of them live in a square-footage chart.
The same stop applies below the line when the footage is split across rooms. A wall unit cannot condition a room it cannot blow air into. An 800 ft² chart row describes one open space a single indoor head can see. Three bedrooms that add up to 800 ft² are a multi-zone job sized room by room, with a load calculation from an HVAC contractor or energy auditor.
Quick answers
What size mini split do I need for 1,000 sq ft?
An open 1,000 ft² floor in climate zone 5 with average insulation needs about 29,000 BTU of heat at 5°F, and screens at 20,000 BTU of cooling, a 24,000 BTU class unit[5]. That heat figure is a load. Most single heads do not reach it at 5°F, so at this size you are comparing cold-climate models by their verified 5°F capacity.
What size mini split for 800 sq ft?
An 800 ft² open space in zone 5 with average insulation screens at 23,000 BTU of heat at 5°F and 17,000 BTU of cooling, an 18,000 BTU class unit[5]. With poor insulation the heating figure rises to 30,000 BTU. Insulation, not footage, decides whether this room is an 18k or a 24k job.
What size mini split for 600 sq ft?
A 600 ft² room in zone 5 with average insulation needs about 17,500 BTU of heat at 5°F and 13,500 BTU of cooling, which rounds up to an 18,000 BTU class unit[5]. In zone 1-2 the same room screens at 8,500 BTU of heat and 16,000 BTU of cooling. Climate zone flips which column drives the choice.
What size mini split for 500 sq ft?
A 500 ft² room in zone 5 with average insulation screens at 14,500 BTU of heat at 5°F and 11,500 BTU of cooling, a 12,000 BTU class unit[5]. That heat figure is higher than the cooling class. A standard 12k unit that holds 6,600 BTU at 5°F will not carry it on a design night, so check the model's 5°F capacity before buying.
What size mini split for 400 sq ft?
A 400 ft² room in zone 5 with average insulation needs about 11,500 BTU of heat at 5°F and 9,500 BTU of cooling, a 12,000 BTU class unit[5]. A typical 2-car garage sits near this size, but garage insulation is rarely average. With poor insulation the same 400 ft² screens at 15,000 BTU of heat.
What size mini split for 300 sq ft?
A 300 ft² room in zone 5 with average insulation screens at 8,500 BTU of heat at 5°F and 7,500 BTU of cooling, a 9,000 BTU class unit[5]. With 2015-or-newer insulation the heating figure drops to 7,500 BTU. A sunroom at this size adds 10% to the cooling side for full sun.
What size mini split for 200 sq ft?
A 200 ft² room in zone 5 with average insulation needs about 6,000 BTU of heat at 5°F and 5,500 BTU of cooling, a 6,000 BTU class unit[5]. That is the smallest common size class, so a well-insulated 200 ft² room is already close to oversized. An oversized unit cools faster than it can pull moisture out of the air, and the room reads cool but feels clammy.
Sources
- ENERGY STAR, Room Air Conditioners (area-to-capacity table; the chart’s cooling base and sun adjustment), accessed August 2026
- Senville product specification page, LETO SENL-12CD, accessed August 2026
- NEEP Cold-Climate Air-Source Heat Pump directory entries: Senville LETO SENL-12CD; MRCOOL DIY 5th Gen 18k, accessed August 2026
- ACCA, Manual J Residential Load Calculation (standard overview), accessed August 2026
- MiniSplitsHQ screening method,
src/lib/sizing-formula.mjs(editorial ceiling, insulation, and climate factors; editorial heating model; 1,400 ft² and 36,000 BTU bounds), verified August 2026
Spec verification process: how we verify specs and prices. Found an error? See the corrections policy on that page.