For an 800-square-foot area, start with an 18,000 BTU/hour room air conditioner. ENERGY STAR places 800 square feet in its 700–1,000-square-foot range, based on an 8-foot ceiling. Treat that as a baseline, not a guarantee: sunlight, occupants, kitchen use, ceiling height and room layout can affect the capacity you need.
What size air conditioner do you need for 800 square feet?
ENERGY STAR recommends 18,000 BTU/hour for spaces in the 700–1,000-square-foot range. Its chart assumes an 8-foot ceiling, so measure the area the unit will actually cool rather than using the square footage of an entire home when only part of it is served. For a rectangular space, multiply its length by its width; for an irregular layout, divide it into simple shapes and add their areas. ENERGY STAR’s room air conditioner sizing guidance also suggests considering greater capacity for higher ceilings.
| Area in ENERGY STAR chart | Recommended capacity |
|---|---|
| 550–700 square feet | 14,000 BTU/hour |
| 700–1,000 square feet | 18,000 BTU/hour |
| 1,000–1,200 square feet | 21,000 BTU/hour |
Adjust the baseline for your room
ENERGY STAR gives these adjustments for its sizing guidance. Apply them to the 18,000 BTU/hour baseline as a starting point, then compare the result with the actual unit’s specifications and installation requirements.
- Heavy shade: reduce the recommended capacity by 10%.
- Very sunny conditions: increase it by 10%.
- Regular occupancy above two people: add 600 BTU/hour for each additional occupant.
- A unit serving a kitchen: add 4,000 BTU/hour.
These factors can interact, and the chart is not a room-by-room load calculation. If the area has unusually high ceilings, an open or awkward layout, or several heat-producing areas, a qualified HVAC professional can help determine an appropriate capacity.
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#1 Best Overall
- PERFECT FOR SMALLER ROOMS - Midea's Affordable Window AC unit is perfect to help your room be as comfortable as possible. It can cool 150 sq. ft. with 7 temperature settings, 2 cooling/2 fan-only speeds, and 2-way air direction to give you the perfect amount of cooling every time.
- ENERGY EFFICIENT- Midea's 5,000 BTU window air conditioner has a Combined Energy Efficiency Rate (CEER) of 11.0 which helps reduce the energy costs to save you money throughout the year.
- QUIET & EASY TO USE - This window AC unit is quieter than a household refrigerator. It also features easy-to-use mechanical controls to quickly set the time, temperature, and mode and has a removable & reusable air filter.
- EASY INSTALLATION - Easily install in your home or apartment's existing window frame. Suitable for windows 23''-36'' wide and minimum 13'' high. 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. Please see included instruction manual for further detail.
- WARRANTY: 1 Year Parts & Labor Warranty comes with each Midea product to ensure the quality of our brand to our customers. Our team is happy to help if any questions or issues arise and make sure to register your product on our website for even faster support in the future.
Why a larger air conditioner is not automatically better
An oversized unit can cool the air quickly and shut off before it has removed enough moisture. The result may feel cool but clammy. Choosing capacity based only on the largest number available can therefore undermine comfort, especially in humid conditions. Match capacity to the space and its conditions rather than assuming extra BTUs are harmless.
18,000 BTU window AC models to investigate
These examples match the chart’s baseline capacity and have manufacturer-listed coverage up to 1,000 square feet. Manufacturer coverage figures are guidance, not independent performance guarantees. The available product information does not establish that either model is a tested overall winner.
Rank #2
- BEST FOR SMALL ROOMS: Cools up to 150 sq ft efficiently with 5,000 BTU cooling power. Ideal for bedrooms, home offices, dorm rooms, workshops, and studio apartments. Compact 16.4" W x 13.4" D x 12.6" H design fits tight spaces.
- QUIET OPERATION - Quieter than many older window AC units, with 2 cooling modes (low 52 dBA for nighttime, high 56 dBA for rapid cooling) and 2 fan speeds for personalized comfort. Simple mechanical controls mean no annoying digital beeps.
- SIMPLE, RELIABLE MECHANICAL CONTROLS: Easy-to-use dials for temperature and fan speed—no Wi-Fi, apps or complex setup required. 10 temperature settings let you dial in your perfect comfort level. Auto restart after power outages.
- LOW MAINTENANCE & ENERGY SMART: No manual draining under normal conditions. Washable, reusable filter for easy care. Low 440W power draw helps reduce energy costs compared to older, inefficient units.
- EASY DIY INSTALLATION: Fixed chassis installs easily and fits double-hung windows 27.125"–36" wide and 13.375" high minimum. EZ Mount kit with foam insulation included. Backed by 1-year GE limited warranty for peace of mind.
| Model | Manufacturer-listed capacity and area | Listed features |
|---|---|---|
| LG LW1816ER | 18,000 BTU; up to 1,000 square feet | Remote control, energy saver mode, four-way airflow and auto restart, according to LG. |
| Midea MAW18RV1CWT | 18,000 BTU DOE; up to 1,000 square feet | Cooling, dehumidifying and fan modes; app and voice control; inverter operation, according to Midea. Midea also claims up to 37% energy savings compared with DOE CEER minimum requirements and operation up to 7X quieter than traditional ACs; these are vendor claims, not independent test results. |
Before choosing either model, verify current specifications, energy-label information, window fit, electrical requirements, price, availability, warranty and return terms. The cited listings do not establish comparative test results or confirm ENERGY STAR certification for these models.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check fit, installation and day-to-day comfort
Capacity is only one part of the decision. A window unit needs to fit the opening and be supported and sealed as its manual specifies. Check the unit’s dimensions, electrical needs and included installation parts; an accessory such as a support bracket or replacement insulation is appropriate only if it is compatible with the AC and window.
Rank #3
- Effortless Cooling: Achieve optimal comfort with customizable temperature settings and two fan speeds; Effortless Temperature Control helps to maintain your preset temperatures for consistent comfort
- Easy Maintenance: Keep your air conditioner running efficiently with the easy-to-clean washable filter, designed to capture dust from the air for long-lasting performance
- Undisturbed Comfort: Experience a peaceful home environment with a quiet performance at 52 dBA – ideal for bedrooms or small spaces up to 150 sq. ft.
- Effortless Convenience: Benefit from the Auto Restart feature, which automatically restores the unit's previous settings once power is restored to the window air conditioner
- Hassle-Free Operation: The extra-long three-prong power cord eliminates the need for extension cords, while the adjustable side panels easily extend to best fit your window, ensuring a secure installation with optimal efficiency and airflow
ENERGY STAR advises following the unit manual and using the included insulation materials. It warns that an improperly installed room air conditioner can leak as much air as a 6-square-inch hole, increasing energy costs and reducing comfort. Keep lamps and TVs away from the AC thermostat so their heat does not make the unit run longer. A fan can help distribute cooled air, and ENERGY STAR recommends setting the AC fan speed low on humid days to remove more moisture.
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