CEER Rating Explained: Combined EER for Window ACs

CEER (Combined Energy Efficiency Ratio) is the efficiency metric for window and portable air conditioners that accounts for both active cooling efficiency and standby power consumption. It replaced the standard EER for room ACs in 2014 because window units draw measurable electricity even when they're plugged in but not actively cooling. A good CEER for a typical 8,000-12,000 BTU window AC is 12.0 or higher, which meets ENERGY STAR certification.

If you're shopping for a window AC, CEER is the number on the EnergyGuide label. Higher CEER means lower electricity bills over the cooling season.

The CEER Formula

CEER = Cooling Capacity (BTU/h) / (Active Power (W) + Standby Power Adjustment (W))

The standby power adjustment accounts for electricity consumed when the unit is in off mode or standby mode (plugged in but compressor not running). The DOE formula weights active and standby power based on assumed annual hours in each mode.

In practice, CEER is slightly lower than EER for the same unit because standby power adds to the denominator. For a unit with 800W active power and 2W standby, the CEER might be 0.1-0.3 points lower than the EER.

CEER Requirements by Capacity

Federal minimum CEER varies by the unit's cooling capacity. Smaller units must meet higher CEER minimums because their compressors are proportionally less efficient:

What's a Good CEER for a Window AC?

CEER vs EER: What Changed

The difference between EER and CEER is small for most units (0.1-0.3 points) because standby power is typically only 1-10W compared to 500-1,500W of active cooling power. But across millions of installed window ACs, the standby draw adds up to significant national energy consumption.

Top Window ACs by CEER (2026)

Calculating Window AC Operating Costs

Annual Cost = (BTU/h / CEER) x Annual Cooling Hours x ($/kWh / 1,000)

Window AC vs Central AC Efficiency

It's tempting to compare window AC CEER to central AC SEER2, but they measure different things:

After accounting for duct losses, a 12 CEER window unit and a 16 SEER2 central system deliver similar actual efficiency to the rooms they serve. The central system's advantage is whole-home coverage and better comfort control.

Portable AC CEER Considerations

Portable air conditioners also carry CEER ratings, but their real-world efficiency is significantly lower than window units for two reasons:

Single-hose portable ACs create negative pressure that pulls warm outdoor air into the room through gaps around doors and windows. This "infiltration load" isn't captured by CEER testing. Dual-hose models partially solve this problem but are less common.

The exhaust hose itself radiates heat back into the room. A 4-5 inch exhaust hose running at 120-140 degrees F through a room adds a measurable heat load.

A portable AC rated at 10 CEER may deliver effective cooling equivalent to only 6-7 CEER once infiltration and hose losses are factored in.

DOE-Adjusted BTU for Portable ACs (Post-2017 Rule)

The DOE test procedure at 10 CFR 430 Subpart B Appendix CC (effective for portable ACs manufactured on or after January 10, 2017) introduced a second cooling-capacity number that appears on product labels alongside the older ASHRAE 128-based rating. Manufacturers must now publish a DOE-adjusted BTU/h value that subtracts two losses the ASHRAE test ignored: infiltration of hot outdoor air pulled in through gaps to replace the air the exhaust hose sends outside, and heat conduction through the hose wall back into the conditioned space.

The adjustment magnitude depends on hose configuration. For single-hose portables, DOE-adjusted capacity is typically 60-80% of the ASHRAE nameplate; dual-hose designs, which pull combustion-style makeup air from outdoors instead of the room, retain roughly 85-95% of the ASHRAE value. Those ranges are the ballparks commonly cited in manufacturer literature filed under the DOE rule, and they explain why the same physical box can carry two very different BTU numbers.

A practical implication: a portable AC marketed as "14,000 BTU (ASHRAE) / 9,500 BTU (DOE-adjusted)" is not equivalent to a 14,000 BTU window unit. The window unit delivers its full nameplate cooling into the room because the entire condenser and hot-side airflow sit outdoors. When sizing a portable against a Manual J load, always use the DOE-adjusted number — the ASHRAE figure overstates delivered cooling by 20-40%.

Reading the EnergyGuide Label

The yellow EnergyGuide label on every new room and portable AC is required by the FTC under 16 CFR Part 305. It packs four pieces of information into a standardized layout, and knowing where to look shortens shopping considerably.

• Top band: manufacturer, model number, and cooling capacity in BTU/h. For portables, this is where the DOE-adjusted number appears; the ASHRAE figure is often relegated to the spec sheet.
• Center: the CEER value for that model, plotted against a horizontal range showing the lowest and highest CEER among similar-capacity units currently on the market. A tick mark shows where this specific model falls on that range.
• Estimated yearly electricity cost: a dollar figure computed at DOE-assumed annual operating hours and a national-average residential electricity price the FTC updates periodically (recent updates have placed the assumed rate near the mid-teens of cents per kWh).
• Bottom disclaimer: a reminder that actual cost varies with usage, climate, and local electricity price.

The estimated-cost figure is a comparative benchmark, not a household forecast. A unit labeled at a modest annual cost under DOE assumptions can easily run two to four times higher in a hot-humid climate where the AC operates most of the day for six or more months. Treat the label's dollar figure the way you'd treat an EPA fuel-economy sticker: excellent for comparing models, unreliable as a personal budget line.

What CEER Doesn't Capture

CEER is measured in a psychrometric chamber under tightly controlled indoor and outdoor conditions specified in 10 CFR 430 Appendix F (for room ACs). Real installations introduce losses the test cannot see, and those losses often matter more than a one-point CEER difference between two models.

• Sleeve and frame leakage. A window unit rattling in an oversized sash gap leaks conditioned air outward and pulls warm air in around the chassis. Foam side-panels, closed-cell weather strip along the sash contact, and a well-sealed accordion filler are the low-cost fix; without them, sensible cooling delivered to the room can drop noticeably even though the compressor draws its rated wattage.
• Warm cavity exposure. When a window AC's rear condenser section sits inside an unconditioned attic knee wall, garage bump-out, or sun-baked porch enclosure, the "outdoor" air the condenser rejects heat into is hotter than the true ambient the DOE test assumes. Higher condensing temperature raises head pressure and cuts capacity.
• Coil fouling. Dust and pollen on the outdoor condenser fins and lint on the indoor evaporator both raise head pressure and lower airflow. A 5-15% efficiency loss by year three without cleaning is a commonly cited industry ballpark; the exact number depends on environment and filter discipline.

CEER remains the right comparative metric when shopping. Once the unit is in the wall, install quality, seasonal maintenance, and honest sizing determine whether the rated efficiency actually shows up on the electric bill.

Key Takeaways

Frequently Asked Questions

Is CEER the same as EER?

CEER is similar to EER but also includes standby power consumption in the calculation. CEER values are typically 0.1-0.3 points lower than EER for the same unit. CEER is used for window and portable ACs, while EER2 is used for central air conditioners.

How much does CEER affect my electricity bill?

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