For a window or through-wall air conditioner, measure the floor area you want to cool and use ENERGY STAR’s capacity chart as a starting point. Then adjust for shade, sun, extra occupants and kitchens. The chart assumes an 8-foot ceiling and is not a method for sizing central air: a whole-home system needs a house-specific load calculation.
First, identify the type of air conditioner
The room-size chart below is intended for room air conditioners, such as window and through-wall units that cool an enclosed space. The U.S. Department of Energy defines a room air conditioner as an encased, single-phase assembly designed for window or through-wall mounting; its definition excludes packaged terminal air conditioners. DOE’s room-air-conditioner overview explains the category.
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If you are choosing equipment for several rooms or an entire house, skip the room-unit chart. Central HVAC capacity depends on the home’s specific heating and cooling loads, not just its total floor area.
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Measure the room in feet. If a measurement is in inches, convert it to a fraction of a foot: for example, 6 inches is 0.5 foot. For a rectangular room, multiply length by width. If the area is irregular, break it into rectangles, squares or triangles and add their areas; for a triangular section, multiply its length by its width and divide by two.
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- Three-in-One Unit: Our 10,000 BTU (5,550 DOE) air conditioner also functions as a dehumidifier & fan. This portable air conditioner has a full function remote control & top mounted control panel with LED display
- Portable AC: Use this personal air conditioner (15.3” x 14” x 24.8") in rooms up to 450 sq. ft. Stay cool in the hot summer months and sleep well with this BLACK+DECKER ac unit for bedroom
- Follow Me Remote: Our portable AC unit comes with a full function remote control that features a FOLLOW ME function, which allows the remote to act as a thermostat for precise temperature control
- Easy Mobility: Thanks to casters on the bottom and side handles on both sides of the small air conditioner, this air cooler can be moved from room to room without any hassle
- Installation Kit: When it comes to fans that blow cold air, this indoor ac unit includes an easy-to-install window kit. A large, vented airflow outlet ushers in cool air
Include only the space the unit is meant to serve. Do not use the whole home’s area to choose a unit for one room.
Use the room-unit capacity chart
Match the measured area to ENERGY STAR’s room-air-conditioner chart. Capacity is given in Btu/h, or British thermal units per hour. The chart assumes an 8-foot ceiling; it is a starting point, not a room-by-room load calculation.
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- Three-in-One Unit: Our 14,000 BTU ASHRAE (10,200 BTU SACC) air conditioner also functions as a dehumidifier & fan. This portable air conditioner has a full function remote control & top mounted control panel with LED display
- Portable AC: Take this personal air conditioner (16.5” x 14.06” x 27.09) in rooms up to 700 sq. ft. Stay cool in the hot summer months and sleep well with this BLACK+DECKER ac unit for bedroom
- Smart AC with Voice Control: This smart air conditioner allows Wi-Fi connectivity and can be controlled using our mobile app available on iOS and Google Play stores, and voice controlled by Amazon Alexa or Google Assistant
- Follow Me Remote: Our portable AC unit comes with a full function remote control that features a FOLLOW ME function, which allows the remote to act as a thermostat for precise temperature control
- Installation Kit: When it comes to fans that blow cold air, this indoor ac unit includes an easy-to-install window kit. A large, vented airflow outlet ushers in cool air
| Area to cool | Starting capacity |
|---|---|
| 100–150 sq ft | 5,000 Btu/h |
| 150–250 sq ft | 6,000 Btu/h |
| 250–300 sq ft | 7,000 Btu/h |
| 300–350 sq ft | 8,000 Btu/h |
| 350–400 sq ft | 9,000 Btu/h |
| 400–450 sq ft | 10,000 Btu/h |
| 450–550 sq ft | 12,000 Btu/h |
| 550–700 sq ft | 14,000 Btu/h |
| 700–1,000 sq ft | 18,000 Btu/h |
| 1,000–1,200 sq ft | 21,000 Btu/h |
| 1,200–1,400 sq ft | 23,000 Btu/h |
| 1,400–1,500 sq ft | 24,000 Btu/h |
| 1,500–2,000 sq ft | 30,000 Btu/h |
ENERGY STAR’s displayed chart includes larger area bands, but the final retrieved entry is truncated, so no capacity is listed here for 2,000–2,500 sq ft. See ENERGY STAR’s room-air-conditioner chart and guidance for the current full chart.
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Adjust for the room’s conditions
After choosing the chart’s starting capacity, apply ENERGY STAR’s adjustments:
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- Fast, Effective Cooling for Rooms Up to 750 Sq. Ft: This 14,000 BTU portable air conditioner provides rapid spot cooling for spaces like bedrooms, home offices, or apartments up to 750 sq. ft. It helps quickly dissipate indoor heat, keeping you comfortable even on the hottest summer days.
- 3-in-1 Versatility: AC, Fan & Dehumidifier: More than just a cooler, this unit also functions as a dehumidifier and a circulating fan. It reduces excess indoor humidity and improves air circulation, delivering year-round comfort across different seasons and weather conditions.
- User-Friendly Controls & Eco-Conscious Design: The clear LED control panel makes operation easy, with a programmable 24-hour timer and Sleep Mode for convenient, quiet nighttime use. Designed with eco-friendly refrigerant, this energy-efficient AC helps cool your space while minimizing energy consumption.
- Easy to Move with Rolling Casters & Side Handles: Compact and sleek, this unit features smooth-rolling wheels and ergonomic side handles, so you can effortlessly move it from room to room — wherever cooling is needed most.
- Quick No-Drill Window Installation: The package includes a remote control and a complete window installation kit with an adjustable exhaust hose and window panels. Fits most double-hung or sliding windows, requires no drilling, and can be set up in minutes — ideal for renters or temporary cooling needs.
- Heavy shade: reduce capacity by 10%.
- Very sunny room: increase capacity by 10%.
- Regular occupants beyond two: add 600 Btu/h for each additional person.
- Kitchen: add 4,000 Btu/h.
These are adjustments to the chart recommendation, not a reason to jump to a much larger unit without considering the other room conditions. ENERGY STAR’s chart does not give a precise formula for higher ceilings; if the room’s ceiling is substantially above 8 feet, the chart’s standard assumption may not fit well, so seek sizing guidance rather than inventing a height multiplier.
Why a larger unit is not automatically better
An oversized room air conditioner can lower the temperature quickly but shut off before it has removed enough moisture. The result may feel cool yet damp or clammy. ENERGY STAR warns that “An oversized air conditioner is less effective, wastes energy and does not provide better cooling.” Its guidance also suggests considering variable-speed compressor technology, which can vary output to control temperature continuously; treat that as a feature to compare, not a requirement for every room.
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- Three-in-One Unit: Our 12,000 BTU (8,350 BTU SACC) air conditioner also functions as a dehumidifier & fan. This portable air conditioner has a full function remote control & top mounted control panel with LED display
- Portable AC: Take this personal air conditioner (16.5” x 14.06” x 27.09) in rooms up to 550 sq. ft. Stay cool in the hot summer months and sleep well with this BLACK+DECKER ac unit for bedroom
- Smart AC with Voice Control: This smart air conditioner allows Wi-Fi connectivity and can be controlled using our mobile app available on iOS and Google Play stores, and voice controlled by Amazon Alexa or Google Assistant
- Follow Me Remote: Our portable AC unit comes with a full function remote control that features a FOLLOW ME function, which allows the remote to act as a thermostat for precise temperature control
- Installation Kit: When it comes to fans that blow cold air, this indoor ac unit includes an easy-to-install window kit. A large, vented airflow outlet ushers in cool air
Choose a model that fits the opening and the room
Once you have a capacity range, compare candidate units on more than the Btu/h label. Check their rated cooling capacity, efficiency, airflow direction and installation requirements. Confirm that the unit fits your window or through-wall opening and that the electrical setup meets the model’s manual. A capacity match will not help if the unit cannot be installed safely or distribute air effectively in the space.
For central air, get a house-specific load calculation
Central-system sizing is a different task from choosing a window unit. The Air Conditioning Contractors of America identifies Manual J, 8th Edition as the ANSI-recognized residential method for calculating equipment sizing loads, and Manual S as the method for selecting equipment using calculated loads, manufacturer performance data and local design conditions. The ACCA pages identify Manual J 8th Edition (2016) and Manual S 3rd Edition, Version 1.02, with 2024 addenda listed; check those pages for updates.
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- 𝗢𝗻𝗲 𝗙𝗮𝗻 𝗳𝗼𝗿 𝗔𝗹𝗹 𝗬𝗼𝘂𝗿 𝗡𝗲𝗲𝗱𝘀: From a gentle breeze to a powerful wind, it adapts to your everyday needs with up to 28 ft/s airflow and a wide oscillation angle to deliver fast, whole-room cooling
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- 𝗥𝗲𝗺𝗼𝘁𝗲 𝗜𝗻𝗰𝗹𝘂𝗱𝗲𝗱 & 𝗘𝗮𝘀𝘆 𝘁𝗼 𝗖𝗹𝗲𝗮𝗻: Adjust settings from bed or the couch with the remote, and when needed, simply remove the back grille for a quick cleaning. The slim design fits perfectly in any bedroom, living room, or office
Ask an HVAC contractor to explain the home-specific load calculation and how the proposed equipment was selected from it. A generic Btu-per-square-foot rule is not equivalent to Manual J and does not account for the conditions of a particular house. The U.S. Department of Energy notes that proper sizing requires accurate heating and cooling loads; improper sizing can increase cost, waste energy and cause excessive on/off cycling that harms comfort and efficiency. DOE Building Science Education’s sizing guidance describes these risks.
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