Free sizing tool
What Size Mini Split Do I Need? Free BTU Calculator
Mini split sizing that starts from the ENERGY STAR chart — then adjusts for sun, ceilings, insulation, climate, and winter heating before matching a Classic America / Vtronix model.
What size mini split do I need? Square footage alone is a rough guess. Classic America's free mini split sizing calculator starts from the ENERGY STAR room air conditioner chart, then adjusts for sun exposure, ceiling height, insulation and windows, people in the room, kitchens, and your climate — and checks winter heating load against each model's published capacity, not just cooling.
Use it for a bedroom, living room, garage or shop, sunroom, basement, ADU, or open floor plan. When you're done, you get a BTU result and a real match from the Classic America lineup (9,000 to 23,000 BTU single-zone, plus the DUET two-zone). Prefer to browse first? Jump to the BTU chart on this page or shop mini splits. New to ductless? See what is a mini split in the FAQ below, then size the room.
Need a hand interpreting the result? Call 1-800-349-4360 Ext. 204 (Mon–Fri, 10 AM–3 PM ET) — Miami Gardens, FL team.
- ENERGY STAR sizing chart
- Cooling and heating checked
- Matched to published model specs
- Multi-room project mode
Which room are you sizing?
Add more rooms any time. Each one gets its own match.
Tell us about Bedroom
These change the load the most.
Type of space
Size
L-shaped room? Split it into two rectangles and add them together, or add each part as its own room.
Ceiling height
Sun exposure
Insulation and windows
People usually in the room
Your climate and power
Applies to every room in this project.
What should it do?
Power at the install spot
Unit style
The method
Why square footage alone gets the size wrong
The ENERGY STAR chart is the right starting point, but it assumes an 8 ft ceiling, average sun and nobody cooking. Two rooms with the same floor area can need very different systems.
Heat comes in through glass and walls, not floor area
A west-facing room with big windows gains far more heat than a shaded one. ENERGY STAR adds or removes 10 percent for sun, and poor insulation pushes the load up further.
Winter can be the bigger job
In cold climates the heating load often exceeds the cooling load. We size for whichever is larger and check it against each model's published heating capacity.
Oversizing is not a safety margin
A unit that is far too big cools the air before it can remove moisture, leaving the room cold and clammy. Inverter mini splits slow down to match the load, so modest headroom is fine; a doubled size is not.
Same 14 x 16 ft bedroom, two different answers
Both rooms are 224 sq ft. Calculated with the tool above.
Shaded room in Ohio
North facing, tight windows. Cold climate, cool and heat, 2 people.
7,300 BTU
Sized for heating. Cooling alone is 4,600 BTU.
Sunny room in Tampa
West facing, older windows. Hot and humid, cool and heat, 3 people.
8,900 BTU
Sized for cooling, 49% above the flat chart.
Flat chart answer for 224 sq ft
What a square-footage-only calculator says.
6,000 BTU
Reference
BTU sizing chart by room size
The ENERGY STAR baseline for an 8 ft ceiling with average sun, and the Classic America model that covers it. Use the calculator above to apply your own adjustments.
| Room area | BTU per hour | Mini split match | Window AC match |
|---|---|---|---|
| Up to 150 sq ft | 5,000 | 9,000 BTU mini split | 8,000 BTU window AC |
| 150 to 250 sq ft | 6,000 | 9,000 BTU mini split | 8,000 BTU window AC |
| 250 to 300 sq ft | 7,000 | 9,000 BTU mini split | 8,000 BTU window AC |
| 300 to 350 sq ft | 8,000 | 9,000 BTU mini split | 8,000 BTU window AC |
| 350 to 400 sq ft | 9,000 | 9,000 BTU mini split | 12,000 BTU window AC |
| 400 to 450 sq ft | 10,000 | 12,000 BTU mini split | 12,000 BTU window AC |
| 450 to 550 sq ft | 12,000 | 12,000 BTU mini split | 12,000 BTU window AC |
| 550 to 700 sq ft | 14,000 | 23,000 BTU mini split or DUET across two rooms | Not available |
| 700 to 1,000 sq ft | 18,000 | 23,000 BTU mini split or DUET across two rooms | Not available |
| 1,000 to 1,200 sq ft | 21,000 | 23,000 BTU mini split | Not available |
| 1,200 to 1,400 sq ft | 23,000 | 23,000 BTU mini split | Not available |
| 1,400 to 1,500 sq ft | 24,000 | 23,000 BTU mini split | Not available |
Baseline capacities from the ENERGY STAR room air conditioner sizing guide. Adjust down 10% for heavy shade, up 10% for very sunny rooms, add 600 BTU per person beyond two and 4,000 BTU for a kitchen.
The lineup
Every Classic America system by cooling capacity
Capacities, voltages and coverage come straight from each model's spec sheet. Coverage is the manufacturer's rating; your room conditions decide the real answer. Compare all specs side by side.
9,000 BTU mini split115V, Up to 400 sq ft9,000
12,000 BTU mini split115V, Up to 550 sq ft12,000
12,000 BTU mini split, 17 SEER2115V, Up to 280 sq ft11,500
DUET 2-zone208/230V, Two rooms18,000
23,000 BTU mini split208/230V, Up to 1,200 sq ft23,000
8,000 BTU window AC115V, 300–350 sq ft8,000
12,000 BTU window AC115V, 400–450 sq ft12,000Choosing a type
Mini split or window AC?
Both are sized in BTU. What separates them is efficiency, heating, noise and how permanent you want the install to be.
Ductless mini split
For rooms you use every day, all year.
- Cooling efficiency
- 17 to 23 SEER2 single-zone, DUET 24 SEER2
- Heating
- Yes, heat pump on every model
- Indoor sound
- From 27 dB on the 9,000 and 12,000 BTU (19 SEER2) models
- Sizes
- 9,000 to 23,000 BTU, plus a 2-zone DUET
- Install
- Wall-mounted, licensed HVAC install recommended
- Window
- Stays free
Window air conditioner
For seasonal cooling, rentals and quick fixes.
- Cooling efficiency
- 12 CEER
- Heating
- No, cooling only
- Indoor sound
- Compressor is inside the window unit
- Sizes
- 8,000 and 12,000 BTU
- Install
- Plug-in, double-hung window, mounting hardware included
- Window
- Occupied while installed
Sizing a whole building or a repeat floor plan?
Contractor mode loads every zone on the job, matches each one and sends the project to our sales team with the quantity you need. The DUET is suggested where two small rooms fit it, at $2,059 for both zones. We quote trade pricing and freight directly.
Garages and outbuildings
Mini split for garage, shed, or workshop
Choose Garage or shop as the room type above: uninsulated walls and a big door add about 25 percent to the load. For insulation tips and what works in sheds and bonus rooms, read mini splits for garages, sheds and bonus rooms.
Questions
Mini split sizing FAQ
How many BTU do I need for a 500 sq ft room?
The ENERGY STAR chart puts 450 to 550 sq ft at 12,000 BTU per hour with an 8 ft ceiling and average sun. A very sunny room adds about 10 percent, a kitchen adds 4,000 BTU, and every person beyond two adds 600. Run the calculator with your details for the adjusted figure, or go straight to the 12,000 BTU mini split.
What happens if my mini split is too big?
An oversized system reaches the set temperature before it has pulled enough moisture out of the air, so the room can feel cool but damp. Inverter mini splits reduce this by slowing the compressor down, which is why modest headroom is fine. Doubling the size you need is not.
What happens if it is too small?
An undersized unit runs flat out on the hottest and coldest days and may not hold the temperature you set. It also works harder for longer, which costs more to run. If your result sits between two sizes, the calculator picks the larger one.
Should I size for cooling or heating?
For whichever load is larger. In hot climates that is almost always cooling. In cold climates the heating load is often bigger, so the calculator estimates both and checks the result against each model's published heating capacity. Our FAQ covers how defrost mode works in winter.
Can a 115V mini split work as well as a 230V one?
Yes, at the sizes it is built for. Classic America's 9,000 and 12,000 BTU systems run on 115V, which suits bedrooms, offices and garages where a 230V circuit is not available. The 23,000 BTU system and the DUET 2-zone need 208/230V. The Install Planner checks your circuit.
Can one mini split cool a whole house?
A single wall unit conditions the space it can blow air into. Open layouts can work; rooms behind closed doors usually need their own indoor unit. For two rooms, the DUET runs two 9,000 BTU indoor units from one outdoor unit. Larger homes are best planned zone by zone in contractor mode, and our team can review the plan: contact us.
Is this a Manual J load calculation?
No. It is a well-adjusted estimate for choosing between models. For new construction, large or unusual spaces, or permit work, have a licensed HVAC professional run a full Manual J calculation. Installers and builders can reach our team through the pro program.
What size mini split do I need for my room?
Start with square footage on the ENERGY STAR chart (for example, many 150–250 sq ft rooms land near 6,000 BTU/h before adjustments), then add or subtract for sun, insulation, ceiling height, people, and kitchens. Run this size finder for an adjusted BTU number and a matched Classic America model — or browse the 9,000, 12,000, and 23,000 BTU product pages.
What is a mini split?
A ductless mini split is an inverter heat-pump system with an outdoor unit and one or more wall-mounted indoor units connected by a refrigerant line set — no ductwork. Classic America / Vtronix systems cool and heat, with WiFi + Alexa on top of the included remote. Compare options on the mini split category or see mini split vs window AC.
From the blog
Sizing reading from the blog
The calculator gives you a number. These explain why getting it right matters, and how awkward spaces change the answer.
Start here10 min readSep 26th 2026
How Many BTU in a Ton? A BTU to Tons Guide for Mini Splits
How many BTU are in a ton, why cartons and contractor quotes use different labels, and how 9k through 24k map before you size the room.
Read the article
24 min readMar 15th 2024
The Crucial Role of Proper Sizing in Mini-Split Systems for Effective Humidity ControlWhy an oversized system leaves a room cold and clammy, and how the right size keeps humidity in check.
316 min readAug 29th 2025
Mini Splits for Garages, Sheds, and Bonus Rooms: Do They Work?Uninsulated walls, big doors and rooms over garages: how to size for spaces the standard chart does not describe.
47 min readJun 9th 2025
Using Mini-Splits in Basements: Humidity Control and ComfortBelow-grade rooms need less cooling but more moisture control. Sizing and placement for basements.- 5
6 min readMar 23rd 2024
Mini Splits are perfect for Accessory Dwelling Units (ADUs)Heating and cooling a whole ADU from one system, and what to plan for in a small footprint.
Keep going
Next steps after sizing
Guides and support