Window Air Conditioner Comparison Chart | How To Pick The Right BTU

Comparing window ACs by BTU and CEER efficiency ensures the coolest, lowest-cost fit for your room size.

Choosing the right window air conditioner comes down to matching cooling capacity to your room’s square footage, then checking efficiency ratings to keep electric bills low. The comparison chart below lays out the numbers that matter.

What To Look For

Window ACs are rated by cooling capacity in Btu/h and efficiency in CEER (Combined Energy Efficiency Ratio). BTU measures cooling power; CEER measures how efficiently electricity is converted into cooling. A higher CEER means lower running costs.

Before shopping, measure your window opening and room’s square footage, and check voltage: most small units run on 115 volts, while larger or through-the-wall units often need 230 volts.

Comparison Chart By Room Size

This chart groups popular models by room size, matching units to space. Prices and specs reflect 2026 listings.

A larger unit will cool a smaller room, but cycles on and off more often, wasting energy and causing temperature swings.

What The ENERGY STAR Label Really Tells You

ENERGY STAR certification means a unit meets U.S. EPA efficiency standards. The bar is rising: the new ENERGY STAR Room Air Conditioner specification takes effect May 26, 2026, and models manufactured on or after that date must meet new rules to earn the label.

New thresholds vary by product class (cooling capacity, louvered sides, window vs. through-the-wall). Through-the-wall units have separate, lower thresholds. For large-room options, see our roundup of the best ACs for large windows.

Both ENERGY STAR status and exact CEER matter. A labeled model is efficient for its class, but comparing CEER directly between two units is the better way to find the least expensive one to run.

Window AC vs Through-The-Wall

These are not interchangeable. Product type is listed separately in ENERGY STAR listings because mounting hardware, sizing sleeve, and airflow design differ significantly.

A window unit sits in the frame; a through-the-wall unit slides into a wall sleeve. Putting a window model into a wall cutout leaks hot air and moisture, and lacks the window’s support. Measure the sleeve if replacing a through-the-wall unit, and note voltage—many run on 230 volts.

ENERGY STAR lists it under “Through-the-Wall,” not “Window.”

Using The ENERGY STAR Product Finder

The official ENERGY STAR product finder lets you compare certified models, filtering by Btu/h, voltage, and product class, and shows CEER and estimated annual kWh use.

When you spot a model, verify its manufacture date against May 26, 2026 if using ENERGY STAR as a criterion. Units built before that date may carry the old label, but newer production models will be most efficient. For example,

To maintain efficiency, clean the filter every couple of weeks during heavy use, keep the front grille clear, and ensure the unit is level so condensation drains properly. A poorly installed unit leaks cool air and runs longer.

For bigger spaces, see our air conditioner for large window recommendations.

FAQs

How many BTU do I need per square foot?

Roughly 20 Btu/h per square foot. A 250-sq-ft room needs about 5,000–6,000 Btu/h, a 400-sq-ft room needs 8,000–10,000 Btu/h, and a 600-sq-ft space needs 12,000–14,000 Btu/h. Heavy sun, high ceilings, or kitchens push you a size up.

Is a higher CEER worth paying for?

Yes, if you run the unit a lot. CEER measures how efficiently the AC converts electricity into cooling, so higher means lower running costs. The price premium often pays for itself in a season or two, especially in hot climates.

What’s the difference between window and through-the-wall ACs?

Installation. A window unit sits in the frame; a through-the-wall unit slides into a permanent sleeve. They aren’t interchangeable without major retrofitting. Through-the-wall units are typically lower-profile and run on 230-volt circuits, while many window units plug into 115-volt outlets.