Best Energy-Efficient Air Conditioners 2026: Window ACs Compared

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It’s the third night of a July heat wave. The bedroom is still 84°F at 10 p.m., the old window unit rattles like a lawn mower, and last month’s electric bill made you wince. A modern inverter window air conditioner fixes all three: it cools the room you’re actually in, it’s quiet enough to sleep next to, and it uses far less electricity than the box it replaces.

The best energy-efficient air conditioner for most rooms is the Midea U-Shaped 10,000 BTU window AC: ENERGY STAR certified with a CEER of 15.0, rated at 500 kWh a year, and its U-shape lets you close the window through it. For small bedrooms, the Windmill 8,000 BTU matches that CEER and is rated at 400 kWh a year.

Below: five room air conditioners compared on CEER, yearly energy use and running cost, how to size one, and why a window unit beats a portable on efficiency. We researched and compared them from ENERGY STAR’s product data and maker pages; we did not test them.

Prices change often. The prices below are what we saw at the maker or a major retailer in October 2026; check the current price before you buy.

Our top picks

Energy-efficient air conditioners compared

Model	Size	CEER	Energy use (ENERGY STAR)	Est. cost/yr*	Room size (maker)	About (Oct 2026)
Midea U-Shaped MAW10V1QWT	10,000 BTU	15.0	500 kWh/yr (38% below federal standard)	about $87	450 sq ft	$419–$450
Windmill 08W2Wi	8,000 BTU	15.0	400 kWh/yr (38% below)	about $69	350 sq ft	$379–$450
LG LW1222IVSM	12,000 BTU	15	600 kWh/yr (38% below)	about $104	550 sq ft	$519
Midea MAW12HV1CWT-A (with heat)	12,000 BTU	13.3	676.7 kWh/yr (36% below)	about $117	550 sq ft	Not seen
Midea Duo MAP14HS1TBL (portable)	12,000 BTU SACC	Not rated by ENERGY STAR	Not listed	n/a	550 sq ft	Not seen

*Our estimate: ENERGY STAR’s yearly kWh (based on the standard test’s assumed hours of use) × 17.30 cents per kWh, the 2025 U.S. residential average (EIA). How many hours you run it, your climate and your rate will change the real number.

What makes a window AC energy-efficient

CEER (Combined Energy Efficiency Ratio) is the number to compare. It’s the cooling a unit delivers per watt-hour, counting standby power too, measured under the Department of Energy test. Higher is better. Among the window and through-the-wall units in ENERGY STAR’s database, the best in the 8,000 to 14,000 BTU range reach a CEER of 17.6; our picks sit at 13.3 to 15.

Inverter compressors are the big change of the last few years. An old unit runs its compressor flat out, then shuts off, then roars back on. An inverter slows down once the room is cool and keeps running gently, which uses less power and is much quieter. Every pick here has one.

The ENERGY STAR label covers window and through-the-wall room air conditioners. ENERGY STAR lists how much less energy each certified model uses than the federal minimum: 36% to 38% for our window picks. Our estimate of what that’s worth: a 10,000 BTU unit using 500 kWh a year, 38% below the standard, compares with roughly 800 kWh for a unit that just meets the minimum, a difference of about 300 kWh, or about $50 a year at the U.S. average rate.

The best energy-efficient air conditioners

1. Midea U-Shaped 10,000 BTU (MAW10V1QWT): best overall

Midea’s U-shaped design straddles the window sash: the noisy compressor sits outside, the quiet part sits inside, and you can close the window down into the “U,” which keeps the opening tighter than an accordion panel. ENERGY STAR lists it at 10,000 BTU, a CEER of 15.0 and 500 kWh a year, 38% below the federal standard. Midea rates it for up to 450 sq ft, with an inverter compressor, Wi-Fi app control and voice assistant support, a washable filter and R-32 refrigerant. It weighs about 54 lb. Midea’s store page lists a 1-year warranty.

• Good: high CEER for the price; quiet U-shape; window still opens and closes; smart controls for scheduling.
• Watch out: cooling only, no heat; heavy for one person to lift into a window; check the window opening sizes in the manual before you order.
• Best for: bedrooms and living rooms of about 300 to 450 sq ft.

Check the Midea U-Shaped price on Amazon

2. Windmill WhisperTech 8,000 BTU (08W2Wi): best for small rooms

Oversizing wastes energy and leaves a room cold and clammy, so a smaller bedroom wants a smaller AC. The Windmill 8,000 BTU is ENERGY STAR certified with a CEER of 15.0 and 400 kWh a year, the lowest yearly use in this guide. Windmill rates it for about 350 sq ft and 6.8 amps, says it “starts at 42 dB,” and uses an inverter compressor and R-32 refrigerant, with app and voice control. The same line comes in 10,000 BTU (CEER 15.0, 500 kWh a year) and 12,000 BTU (CEER 13.5). Windmill’s warranty is 1 year.

• Good: lowest yearly energy use here; low amp draw; quiet inverter; simple install.
• Watch out: 1-year warranty; standard box shape, so the window is blocked; make sure the size you order is the one you want (it’s sold in several sizes).
• Best for: bedrooms and home offices up to about 350 sq ft.

Check the Windmill AC price on Amazon

3. LG DUAL Inverter 12,000 BTU (LW1222IVSM): best for large rooms

For an open living room or a big main bedroom, LG’s 12,000 BTU DUAL Inverter keeps the efficiency of the smaller picks: ENERGY STAR lists a CEER of 15 and 600 kWh a year, 38% below the federal standard. LG rates it for up to 550 sq ft and quotes operation down to 44 dB, with Wi-Fi control through the LG ThinQ app and voice assistants, and R-32 refrigerant. LG’s price was $519 when we checked, with a 1-year parts warranty. Larger units draw more current, so check whether yours needs its own circuit (see “How to choose” below).

• Good: high CEER at 12,000 BTU; quiet; app scheduling.
• Watch out: big and heavy; 1-year parts warranty; may need a dedicated circuit.
• Best for: rooms of about 450 to 550 sq ft.

See it at LG

4. Midea 12,000 BTU Window AC with Heat (MAW12HV1CWT-A): best with heat for spring and fall

This one is a small heat pump in a window: it cools in summer and, in mild weather, runs in reverse to heat. ENERGY STAR lists a CEER of 13.3 and 676.7 kWh a year of cooling energy, 36% below the federal standard, with heating mode and an inverter compressor. The catch is cold weather: the heat pump stops working below about 41°F outside, so it’s spring-and-fall heat, not a winter heater. For those cool mornings, though, it heats far more efficiently than a space heater. It runs on 115 V, uses R-32 refrigerant and carries a 1-year warranty.

• Good: cooling and mild-weather heat in one unit; inverter; ENERGY STAR.
• Watch out: lower CEER than the cool-only picks; no heat pump heat below about 41°F; Midea’s page doesn’t list a heating BTU figure.
• Best for: mild climates and shoulder seasons. For real winter heat, see our best window heat pumps.

Check the Midea window AC with heat price on Amazon

5. Midea Duo Portable (MAP14HS1TBL): best if a window unit won’t fit

Some windows (casements, sliders, rental rules) just won’t take a window AC. If a portable is your only option, a dual-hose inverter model like the Midea Duo wastes less than a single-hose unit, because it pulls outdoor air through one hose to cool its condenser instead of pushing your cooled room air outside. Midea rates it at 12,000 BTU under the DOE test (14,000 BTU ASHRAE), for up to 550 sq ft, with heat pump heating in mild weather (about 41°F and up), app control and “as low as 42 dBA.” It weighs about 77 lb and has a 1-year warranty.

Be clear about the trade-off: ENERGY STAR’s room air conditioner program covers window and through-the-wall units only, so no portable carries the label. Consumer Reports calls portables “a last resort” and found they cool much more slowly than window units.

• Good: no window installation; dual hose and inverter; cools and heats.
• Watch out: less efficient than any window pick; heavy; takes floor space; hoses still need a window opening.
• Best for: rooms where a window unit truly isn’t possible.

Check the Midea Duo price on Amazon

Also worth a look: the GE Profile ClearView 10,300 BTU (PHNT10CC) is an ENERGY STAR saddle unit (CEER 14.7, 525.5 kWh a year) that leaves most of the window clear. GE lists it as no longer manufactured, so buy it only if you find one on clearance.

How to choose an energy-efficient air conditioner

• Size it to the room. DOE’s rule of thumb is about 20 BTU per square foot. ENERGY STAR’s chart: 150–250 sq ft, 6,000 BTU; 300–350 sq ft, 8,000 BTU; 400–450 sq ft, 10,000 BTU; 450–550 sq ft, 12,000 BTU. Add capacity for a sunny room or a kitchen. DOE warns that an oversized unit cools too fast without removing humidity.
• Compare CEER and yearly kWh, not marketing percentages. Look for the ENERGY STAR label and an inverter compressor.
• Check the circuit. DOE says units under 7.5 amps can plug into any 15- or 20-amp, 120-volt circuit not shared with major appliances; larger units need a dedicated 115-volt circuit, and the biggest need 240 volts. Any new circuit is a job for a licensed electrician, with a permit where required. Don’t use an extension cord unless the AC’s manual allows it.
• Seal it well. ENERGY STAR says a badly installed room AC leaks as much air as a 6-square-inch hole. Use the included insulation panels, keep it level so it drains, and seal gaps around it. Window film and weatherstripping help the rest of the room too.
• Set it and leave it. DOE advises setting the thermostat as high as is comfortable and not setting it colder than needed, which doesn’t cool faster. A ceiling or box fan helps spread the cool air for little extra power.
• Check rebates. Some utilities offer rebates on ENERGY STAR room ACs; use the ENERGY STAR Rebate Finder and your utility’s site. We can’t promise money in any area.

Keep exploring

Start with our guide on how to lower your electric bill, then read how to lower your electric bill in summer and time-of-use rates (running AC before the peak hours can cut costs). In humid climates, pair your AC with one of the best energy-efficient dehumidifiers. If you’re thinking bigger, compare a heat pump for the whole house. Learn the basics in electrical energy and thermal energy, and browse every energy-saving tip.

Energy-efficient air conditioner questions

What is the most energy-efficient window air conditioner?

Compare CEER on the ENERGY STAR product finder; the highest-rated 8,000–14,000 BTU units reach 17.6. Among the models we compared, the Midea U-Shaped 10,000 BTU, Windmill 8,000 BTU and LG 12,000 BTU all have a CEER of 15, and the Windmill uses the least energy a year, 400 kWh.

What is a good CEER rating?

For a window AC in 2026, a CEER of about 15 is excellent for the money, and ENERGY STAR’s best in the common sizes reach 17.6. The higher the number, the more cooling you get per kilowatt-hour. Compare models of the same size, since requirements differ by capacity.

How much does it cost to run a window air conditioner?

Our estimate from ENERGY STAR’s yearly figures at 17.30 cents per kWh: about $69 a year for the Windmill 8,000 BTU, about $87 for the Midea 10,000 BTU and about $104 for the LG 12,000 BTU. Run it more hours, live somewhere hot or pay more per kWh and it costs more.

Are portable air conditioners less efficient than window units?

Yes. A portable sits inside the room, so heat from the unit and its hose stays indoors, and single-hose models also pull warm air in through gaps. ENERGY STAR doesn’t certify portables, and Consumer Reports calls them a last resort. If you must use one, choose a dual-hose inverter model.

Is it cheaper to run a window AC or central air?

DOE says room air conditioners are less expensive to operate than central units because they cool one room, though their efficiency is generally lower. Cooling one or two rooms with efficient window units and letting the rest of the house stay warmer usually costs less than cooling the whole house.

What size air conditioner do I need?

About 20 BTU per square foot (DOE). ENERGY STAR’s chart suggests 8,000 BTU for 300–350 sq ft, 10,000 BTU for 400–450 sq ft and 12,000 BTU for 450–550 sq ft. Go a bit larger for sunny rooms or kitchens; don’t oversize, or the room will feel clammy.