Understanding Star Ratings & ISEER in Inverter ACs
In 2026, the old EER (Energy Efficiency Ratio) has been replaced by ISEER (Indian Seasonal Energy Efficiency Ratio) for all air conditioners sold in India.
What is ISEER?
Standard ACs run at one speed. Inverter ACs vary their speed, becoming 0.15 Ton to 2.25 Ton machines as needed. ISEER was created to measure this variable efficiency across the changing Indian seasons.
The ISEER Formula
The efficiency is calculated as a ratio of cooling produced to energy consumed over a standard year.
ISEER =
Total Annual Cooling Output (Watts)
Total Annual Electricity Consumption (Watts)
How BEE Calculates Your Rating:
- Usage Assumption: BEE assumes the AC runs for 1,600 hours a year.
- Temperature Profile: It uses weather data from 54 Indian cities, ranging from 24°C to 43°C.
- The "Efficiency Drift": Efficiency standards tighten every few years. A 5-star AC from 2018 might only be a 1-star or 2-star AC under the 2026 standards.
Highest ISEER Rating AC India
The Highest ISEER Rating ACs in India as of 2026 start is
Daikin's FTKF series
with a rating of 6.3. This makes this 5 Star AC the stand out energy efficient AC of 2026.
Another best ISEER rated AC is Blue Star's Q Series 5 star ACs Blue Star's Q Series 5 star ACs achieving ISEER of 6.5
3-Star vs. 5-Star: Which to Choose?
- 5-Star AC: Minimum ISEER of ~5.0+ (as per 2024-2027 labels).
- 3-Star AC: Minimum ISEER of ~3.8 - 4.3.
Engineer's Advice: If you use your AC for more than 6-8 hours a day, especially during the peak of summer, a 5-star AC is an investment that pays for itself in lower monthly bills.
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Further Reading in this Series: