Choose a window AC by measuring the floor area it will cool, then use ENERGY STAR’s capacity chart as a baseline for a room with an 8-foot ceiling. Adjust for strong sun or heavy shade, regular occupants beyond two, and kitchen heat. A unit that is too large can cool the air quickly without removing enough humidity, leaving the room clammy.
Measure the area you want to cool
Size the unit for the room or connected area it is meant to serve—not automatically for the whole home. For a rectangular room, multiply its length by its width. Convert inches to feet first: 12 feet 6 inches is 12.5 feet. For a triangular area, multiply length by width and divide by two. For an irregular layout, split the space into rectangles, squares, and triangles, calculate each section, and add the areas.
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The ENERGY STAR chart below assumes an 8-foot ceiling. Its recommendations are starting points, not guarantees that every room with the same floor area will cool equally well. ENERGY STAR advises considering greater capacity for higher ceilings but does not specify a ceiling-height multiplier. Areas under 100 square feet and over 2,500 square feet are outside the chart; do not extrapolate a precise capacity from it.
Use the room-size BTU chart
BTU/h means British thermal units per hour, the measure of an air conditioner’s cooling capacity. Match your measured area to the corresponding ENERGY STAR range:
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| Area to be cooled | Baseline 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 |
| 2,000–2,500 sq ft | 34,000 BTU/h |
For example, ENERGY STAR’s baseline is 5,000 BTU/h for 100–150 square feet and 8,000 BTU/h for 300–350 square feet. A 700–1,000-square-foot area maps to 18,000 BTU/h. Use the range containing your measured area, then apply the relevant adjustments below. See ENERGY STAR’s room AC sizing guidance.
Adjust the baseline for the room
Apply the adjustments ENERGY STAR specifies to the chart capacity:
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- 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.
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- 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.
- Heavy shade: reduce capacity by 10%.
- Very sunny room: increase capacity by 10%.
- More than two regular occupants: add 600 BTU/h for each additional person.
- Kitchen: add 4,000 BTU/h.
For example, a very sunny 300–350-square-foot room starts at 8,000 BTU/h; the 10% sun adjustment adds 800 BTU/h, for a 8,800 BTU/h target before any applicable occupant or kitchen adjustment. If the unit will sit near a corner, check that its airflow can be directed into the room. The guidance mentions higher ceilings but gives no numeric adjustment, so it does not support a precise ceiling-based calculation.
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Why a bigger unit is not automatically better
An oversized room AC can lower the room temperature before it has removed enough moisture from the air. The result may feel damp or clammy even though the room is cooler. Use the adjusted capacity as a target rather than buying extra capacity “just in case.” The ENERGY STAR chart is a general sizing guide; it does not provide a quantified formula for insulation, climate, or complex open-plan layouts.
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- 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
Check efficiency and window fit
Once you have an adjusted capacity target, compare models on cooling capacity, efficiency, and whether they can be installed and positioned correctly in your window and room.
- Match capacity: compare the unit’s rated cooling capacity with your adjusted target.
- Check certification and efficiency: look for ENERGY STAR certification and compare the applicable CEER criteria. ENERGY STAR says certified room ACs are 19–36% more energy efficient than federal minimum standards, depending on product criteria; the range is not a single threshold that applies to every model. Review the room AC product criteria.
- Confirm installation compatibility: check the manufacturer’s installation instructions and the window’s dimensions and configuration. Some ENERGY STAR-certified models use a U-shaped or saddle design around the windowsill.
- Consider airflow: make sure the installed unit can direct cool air through the area you intend it to serve, especially in a corner or irregular layout.
For installation materials or insulation, follow the unit manufacturer’s instructions rather than assuming one accessory or method fits every model. ENERGY STAR’s 2025 room air conditioner factsheet provides additional program context.
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