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For a typical 300-square-foot room with an 8-foot ceiling, start with an 8,000-BTU/h room air conditioner. That is the lower end of ENERGY STAR’s 300-to-350-square-foot sizing band, not a guarantee that every 8,000-BTU unit will suit your room. Sun exposure, ceiling height, occupants, kitchen heat, window fit, and the unit’s efficiency all matter.
How many BTUs do you need for 300 square feet?
ENERGY STAR recommends 8,000 BTU/h for a room from 300 up to 350 square feet, assuming an 8-foot ceiling. Its guidance is for room air conditioners and is U.S.-oriented. Measure the room’s length and width and multiply them to find the area. For an irregular floor plan, divide it into simple shapes, calculate each area, and add them together. ENERGY STAR’s room air conditioner guidance provides the sizing chart.
| Room area | ENERGY STAR capacity guidance |
|---|---|
| 250 up to 300 sq. ft. | 7,000 BTU/h |
| 300 up to 350 sq. ft. | 8,000 BTU/h |
| 350 up to 400 sq. ft. | 9,000 BTU/h |
| 400 up to 450 sq. ft. | 10,000 BTU/h |
| 450 up to 550 sq. ft. | 12,000 BTU/h |
The chart is a starting point: ENERGY STAR says higher ceilings may require greater capacity. Its guidance also calls for adjusting the sizing estimate based on the room’s conditions:
- Reduce capacity by 10% for a heavily shaded room.
- Increase capacity by 10% for a very sunny room.
- Add 600 BTU for each regular occupant above two.
- Add 4,000 BTU if the air conditioner serves a kitchen.
For example, a very sunny 300-square-foot room may need more capacity than the baseline estimate, while heavy shade points in the opposite direction. Use the adjustments as sizing guidance rather than assuming that the largest available unit is best.
#1 Best Overall
- 3 IN 1 COMFORT - The Midea EasyCool Window Air Conditioner unit has three modes to help your house, apartment, office, or room be as comfortable as possible. It can cool a space up to 250 sq. ft. quickly, circulate air with its 3-speed fan, or reduce humidity utilizing the dehumidifier mode.
- QUIET & EASY TO USE - This window AC unit is low as 52dB(low mode). The intuitive LED display and remote control (batteries included) allow easy setting of time, temperature, and mode from across the room. The removable and reusable air filter protects your family and living space from dust and pet hairs.
- EASY INSTALLATION - Install easily in your home or apartment's existing window frame (23"-36"x14"). All mounting accessories are included. A screwdriver is required (but not included) for installation. For some window frames, pilot holes are recommended before installing screws. Installation instructions are simple and setting it up is a breeze.
- WORLDWIDE LEADER - Midea is the air treatment brand with a motto to help make customers feel at home with each of their products. As a testament to our dedication to quality and our customers, we offer one-year parts and labor warranty on this product.
- ENERGY EFFICIENT - The EasyCool window air conditioner helps save you money throughout the year. There are also multiple custom settings to help you be even more energy-efficient like Eco mode and an EasyTimer feature to program a schedule that fits your needs.
Why an oversized air conditioner can feel worse
A higher BTU rating is not automatically an upgrade. ENERGY STAR warns that an oversized unit can cool the air before it removes enough humidity, leaving the room cool but clammy. It can also cost more and waste energy. As ENERGY STAR puts it, “Remember that bigger is not always better!”
Choose capacity to suit the room and its conditions, then compare operating style and efficiency. ENERGY STAR recommends considering variable-speed compressors, which can modulate output to regulate temperature quietly. It also identifies ENERGY STAR certification and lower-global-warming-potential refrigerants as relevant selection considerations. Check the exact model’s current certification and refrigerant rather than inferring either from the brand or product family; ENERGY STAR lists R-32, R-454B, and R-290 among lower-GWP room-AC refrigerants.
Rank #2
- Multi-Season Comfort - Midea 8000 BTU window air conditioner with heat is better than standard ac units. It will beat the heat in summer with powerful cooling and dehumidification and keep you warm through the fall with supplemental heat. Best for large rooms up to 350 square feet. NOTE: heat pump function works when outside temp> 41°F.
- Easy To Use – This air conditioner and heat unit comes with an LED display, 5 Modes (Heat, Auto, Cool, Dry, Fan), 3 speed settings (Auto/H/M/L), 24-hr Timer, and ECO energy saver. The Swing button adjusts the louvers up/down to direct the airflow. Wireless control enabled window ac with heat unit from anywhere with the SmartHome App, or with your voice via Alexa and Google Assistant. All functions can be set via the control panel, remote control, and app or voice assistant.
- Save Energy Being Cool – Save on energy costs and enjoy ultimate comfort with this energy star certified unit. This energy efficient air conditioner unit is engineered with variable-speed inverter technology that will quickly cool your bedroom or apartment space while using considerably less electricity; up to 35% energy savings compared to the Energy Conservation Standard. Washable filter is easily accessed from front panel for regular cleaning to maintain peak performance.
- Ultra Low Noise Performance – This ac window unit operates at a noise level as low as 45 dBA. It’s such a quiet air conditioner that you will barely notice it, even when it’s on high. Enjoy your Zoom call, watch your favorite TV show, have a conversation. This ac unit for bedroom also creates just the right amount of white noise so you can get some rest.
- Install Specs – This window air conditioner is designed to fit double hung windows with opening widths of 24 to 38.5 inches. Lower sash must open sufficiently to allow a clear vertical opening of 14.5 inches. AC window unit measures 19.41"W x 22.17"D x 13.9"H. Included components: 8000 btu window air conditioner, remote control, installation kit. This ac heater combo window unit is as a close as you can get to a mini split a/c. You may like it so much you just might buy two!
Which 8,000-BTU window air conditioners are worth comparing?
For a room near 300 square feet, “8,000 BTU window air conditioner” is a useful starting category for shopping. The examples below come from Tom’s Guide’s June 25, 2026 buying guide; they are editorial listings, not a claim that every size is currently available or ENERGY STAR certified. Tom’s Guide’s smart air conditioner guide lists these options:
| Example | Listed capacity and room estimate | What to know |
|---|---|---|
| LG Dual Inverter window AC | 8,000 BTU; 340 sq. ft. | Tom’s Guide describes variable-speed dual-inverter operation. Its reviewer’s personal-use comments concern a 10,000-BTU model, not the 8,000-BTU version. |
| Windmill window AC | 8,300 BTU; 350 sq. ft. | Tom’s Guide describes this size as smart-enabled. |
| Hisense smart window AC | 8,000 BTU; about 350 sq. ft. | Tom’s Guide reports 43 dB in its own test of the 8,000-BTU model’s quiet mode. That is the publication’s test result, not independent lab verification or a guarantee for every installation. |
These room-size estimates are product-guide figures, not substitutes for measuring your space or checking the manufacturer’s specifications. Before choosing a model, verify its exact model number, rated capacity, dimensions, window requirements, current ENERGY STAR status, warranty, and price. Compare CEER or another stated efficiency measure, compressor type, noise claims, controls, airflow direction, and refrigerant as well as BTUs.
Rank #3
- POWERFUL COOLING: Featured with latest compressor and copper motor, efficiently cools down your room or office with this window air conditioner, covering a generous area. Moreover, we can operate it in the form of a dehumidifier or fan-only function. Perfect choice for your room like home, office, or apartment
- ENERGY SAVING: With the advanced Inverter technology, this window ac unit gives you 35% more energy-savings compared to other traditional units. A 15.0 CEER rating & ECO-friendly design which leads you for low electricity & money saving
- ULTRA QUIET: Ultra Silent at only 42dBA in sleep mode instead of others 55dBA and its beautifully built adds a touch of elegant charm to your room. Featured with 4-way swing function, unit provides scientic airflow in your room to suit your comforts in just a few minutes. Best choice to decorate your home
- WIFI-ENABLED & VOICE CONTROL: Beside of the panel & remote control, seamlessly integrate with phone APP or voice control (works with Alexa/Google Assistant); Set routines for optimal temperature changes allows you to adjust your window air conditioner from anywhere so that you can enjoy endless comfort immediately once arriving home
- SIMPLE INSTALLATION: Thanks to its pre-assembled design of side panels, this AC unit saves you at least 30% time on installation compared to traditional window AC units. Easy steps of sliding it in and securing with screws included (windows width: 24" - 36"; window height: 14.5")
Check window fit and installation before you buy
A unit that suits the room still needs to fit the opening and be installed as directed. Measure the window and compare it with the AC’s installation requirements, including window style and dimensions. ENERGY STAR notes that U-shaped or saddle-style designs can leave the window operable and position the compressor outside the room. Follow the exact unit manual and use the included insulation materials to seal the installation. ENERGY STAR’s Most Efficient 2025 room air conditioner guidance provides additional installation context.
Consider where the unit will sit and how air will move through the room; ENERGY STAR advises considering airflow direction when an AC is near a corner. A suitable installation or sealing kit may help, but compatibility depends on the specific unit and window.
Rank #4
- POWERFUL COOLING: The Shiny Series portable AC offers 10,200 BTU ASHRAE (6200 BTU SACC) of cool air, making it flawless for cooling spaces up to 400 square feet, such as your home office, bedroom, or living room. With a CFM of 206, all areas of the room can be cooled in as little as 20 minutes.
- SMART-HOME CONTROL: The free Gree+ App, allows for easy and convenient control of your AC unit from anywhere. With WiFi smart control and the included remote, you can customize your cooling preferences so you always come home to a cool and comfortable space.
- EASY INSTALLATION: The included window-installation kit is easy to install and allows for venting of the heat from the back side of the AC unit. The exhaust hose can be extended from 11.8 inches to 58.8 inches, and the flexible connection panel fits into most window openings between 9.1 and 62 inches.
- ADDITIONAL FEATURES: With additional dehumidifier and fan functions, this AC unit helps you stay comfortable on muggy and humid days. The unit will start removing 2.5 pints (1.2L/hour) of water from the air in dehumidify mode, ensuring fresh and clean air in your home.
- HIGHER STANDARD: The copper core compressors ensure stable cooling performance and a longer unit lifespan, keeping you comfortable even in the hottest weather for years to come.
How to compare efficiency claims fairly
DOE FEMP’s room-air-conditioner purchasing guidance, updated in December 2024, covers casement-only and casement-slider window ACs, through-the-wall units, and reverse-cycle room ACs. It excludes portable air conditioners, so its comparisons should not be applied to portable models. DOE FEMP’s purchasing guidance also illustrates why efficiency figures need their assumptions attached.
For a non-reverse-cycle example, FEMP lists best-available, ENERGY STAR, and less-efficient models at CEER 15.4, 14.7, and 10.9, with annual energy use of 584, 612, and 826 kWh, respectively. Under its stated assumptions, nine-year lifetime energy-cost savings versus the less-efficient baseline are $189 for the best-available model and $167 for the ENERGY STAR model. These are not savings forecasts for a 300-square-foot room: the example assumes a 12,000-BTU unit used 750 hours per year, electricity at 11.1 cents/kWh (the stated federal-facility average as of July 2024), a nine-year life, and product-efficiency data as of December 2024.
Best Value
- 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
For an individual room, electricity costs depend on the chosen unit’s efficiency and how often it runs, as well as local electricity rates and room conditions. Compare models using the same kind of efficiency measure where possible and keep the rating attached to the exact model you are considering.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
