Look for high (Seasonal Energy Efficiency Ratio) ratings. A higher rating means lower monthly electricity bills. SEER2 18–20: A solid, cost-effective baseline.

Add 10% for very sunny rooms; subtract 10% for heavily shaded ones.

Excellent for primary-use rooms where the unit runs daily.

Add 4,000 BTUs if the unit is installed in a kitchen due to appliance heat. 2. Choosing the Right Efficiency (SEER2)

The most critical step is matching the unit's cooling and heating capacity, measured in British Thermal Units (BTUs), to your room size. A unit that is too small won't cool effectively, while one that is too large will "short-cycle," turning on and off too frequently, which wastes energy and fails to dehumidify. Room Size (sq. ft.) Recommended BTUs 150 – 300 6,000 – 9,000 300 – 550 9,000 – 12,000 550 – 800 12,000 – 18,000 800 – 1,100 18,000 – 24,000 1,100 – 1,500 24,000 – 36,000