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Reviewed / Tara Jacoby
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Whenever summer approaches and threatens record-breaking temperatures, you likely think about the best ways to cool your home. If you're at all energy-conscious, you also consider the most efficient ways to cool your home.
While some homeowners are transitioning to heat pumps or geothermal exchange systems thanks to tax credits and incentives, many people have no choice but to rely on traditional air conditioners to cool off, which aren’t known for being incredibly environmentally friendly.
Heating and cooling are also among the most significant expenses in the home, and even if you usually use Energy Saver mode on your air conditioners, you may need to learn how to economize while cooling.
Whether you’re looking to buy a new unit that will reduce your environmental impact or want advice on maximizing your air conditioner’s efficiency and lowering your bills, here are a few things to look for and terms to understand to get the most out of your AC.
One of the most important things to know before installing an air conditioner is whether it’s the right size for your room or home. An AC that’s too big or too small for its space won’t cool the room properly and will result in sub-par performance, so the first thing to do is measure the square footage of the space you hope to cool.
British Thermal Units, or BTUs, are used to measure the size of an air conditioner, ranging from 5,000 BTUs, which can cool smaller rooms, to 34,000 BTUs for a 2,500-square-foot home.
It's a common misconception that buying a bigger model will cool off a small space quickly. However, according to the Energy Star website, “a unit that is too big will be less effective and offer reduced air conditioner efficiency.” This is because air conditioners remove both heat and humidity from the air.
If a unit is too big for the room it’s in, it will cool the air before it has a chance to remove humidity, resulting in an uncomfortably damp, clammy space. So, it's best to measure your space before you shop, rather than buying an unnecessarily huge appliance or grabbing whatever is on sale.
BTUs per Room Size
| Area To Be Cooled (square feet) | Capacity Needed (BTUs per hour) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
| 450 up to 550 | 12,000 |
| 550 up to 700 | 14,000 |
| 700 up to 1,000 | 18,000 |
| 1,000 up to 1,200 | 21,000 |
| 1,200 up to 1,400 | 23,000 |
| 1,400 up to 1,500 | 24,000 |
| 1,500 up to 2,000 | 30,000 |
| 2,000 up to 2,500 | 34,000 |
Information provided by Energy Star.
For optimal efficiency, many newer air conditioners feature variable-speed compressors, also called inverter compressors. These allow a room’s temperature to be continuously controlled rather than toggling on and off when it reaches its desired temperature. In our research, most current models clearly indicate whether their compressors are variable-speed or inverter-type.
If greenhouse gases and the environment are top of mind while you shop for a new AC unit, there are two acronyms you can keep an eye out for: GWP and CEER. GWP refers to the global warming potential of the refrigerant used in the machine.
The GWP compares the warming potential of a refrigerant to that of an equivalent amount of CO2. Many air conditioners rely on hydrofluorocarbons (HFCs) as refrigerants, and their GWP is hundreds or even thousands of times higher than that of CO2.
We’ve noticed that many retailers and company websites are transparent about which coolants their air conditioners use, so it’s easy to find those with lower global warming potential.
These coolants are labeled R-410A, R-407C, R-32 or HFC-32, R-454B, or R-290. While those listed above are still HFCs, they’re an improvement over coolants of the past, like Freon and other ozone-depleting chlorofluorocarbons used in older ACs. (If you can’t locate a product’s coolant type online or on its packaging, the Energy Star website lists the specific coolants most major brands use.)
The other acronym to look for is CEER, which stands for Combined Energy Efficiency Ratio (also sometimes listed as EER). This is essentially a grade every air conditioner receives; the higher the CEER, the more efficient the appliance.
Energy Star’s top-rated Most Efficient 2025 air conditioners, which all have a CEER of 15 or higher, are window units that feature variable-speed compressors and use the lower-GWP refrigerant R-32. Midea manufactures the vast majority of these most energy-efficient performers, but there are also models from LG and Friedrich.
As of 2025, this Midea window air conditioning unit is listed at the top of Energy Star's list, with a CEER rating of 17.6. It features 5,000 BTU with heat.
With 6,000 BTUs of cooling power, the LG DUAL Inverter Smart Wi-Fi Enabled Window Air Conditioner can cool smaller rooms, up to 260 sq. ft., can be programmed and controlled by your phone, and has a 15.5 CEER rating.
This 8,000 BTU air conditioner ranks extremely high on the Energy Star scale. It has a CEER rating of 16 and smart capabilities.
Portable air conditioners (PACs) have become a modern convenience for many who don’t have a place to install a window unit. Still, currently, none are recommended or rated by Energy Star.
One more portable cooling option that’s significantly more energy-efficient than an AC is an evaporative cooler. These fans are not true air conditioners; they contain no refrigerant. They blow cool, evaporated water through the air to cool off hot, dry rooms.
It can take some time to understand what to look for when buying an efficient air conditioner, but a little bit of research in advance can save you loads of money over time and can be its own reward when the dog days of summer arrive.
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