What SEER2 tells you
SEER2 is a standardized seasonal cooling-efficiency rating. It relates cooling delivered in Btu to electrical energy in watt-hours over the prescribed cooling season. Higher values indicate more cooling per unit of electricity under that procedure. ENERGY STAR provides the formal SEER2 definition.
The rating is useful for comparing suitable matched systems. It does not tell you how many hours your equipment will run, the electricity rate you pay, or whether the ducts distribute air well. It also does not measure heating efficiency; that is a different comparison for heat pumps.
Estimate the relative reduction
For a simplified comparison with the same delivered cooling and otherwise equivalent conditions:
Estimated cooling-energy reduction = 1 − old efficiency ÷ new efficiency.
Moving from 14 SEER2 to 18 SEER2 gives 1 − 14/18 = 22.2%. This does not mean the higher number is “four percent better,” and it does not promise a 22.2% reduction in the entire electric bill.
| Illustrative comparison | Simplified reduction in cooling electricity |
|---|---|
| 14 to 16 SEER2 | 12.5% |
| 14 to 18 SEER2 | 22.2% |
| 16 to 20 SEER2 | 20.0% |
| 18 to 20 SEER2 | 10.0% |
These calculations use hypothetical like-for-like ratings. They are not verified field savings for a particular pair of products. The actual system combination, climate, control behavior, and installation can change results.
Apply savings to the right baseline
Suppose cooling accounts for an estimated 2,000 kWh annually, and electricity costs an assumed $0.18/kWh. Cooling expense is $360. A 22.2% reduction would save about 444 kWh or $80 per year. If the entire household bill is $2,000, applying 22.2% to all of it would incorrectly claim $444 of savings.
In a different illustrative home using 5,000 kWh for cooling at $0.30/kWh, the same relative reduction is worth about $333 annually. The equipment-rating comparison has not changed; cooling use and electricity price have. This is why climate and tariff matter to the value of an efficiency upgrade.
If you do not know the cooling baseline, build a range. Separate other summer loads where possible and compare weather and billing days. The AC running-cost guide explains an input-power and runtime method.
Test the added purchase price
Divide the incremental installed cost by estimated annual savings for a simple payback. A hypothetical $1,200 premium divided by $80 is 15 years. The same premium divided by $333 is about 3.6 years. Neither calculation includes financing, maintenance differences, future rates, or the time value of money.
DOE’s purchasing guidance treats efficiency premiums through life-cycle cost comparisons and regional assumptions. Its example results should not be copied into a household estimate without checking those assumptions. Use your actual quotes, and compare equipment with similar installation scope and comfort features.
Do not mix old and new rating systems casually
SEER and SEER2 come from different test procedures. A lower SEER2 number than an older SEER number does not necessarily mean a product became less efficient. Compare ratings on the same basis and request certified matched-system information for the exact indoor and outdoor models.
Avoid a universal conversion factor used as if it were a precise product rating. If a bid provides only an old SEER figure, ask for the relevant current certification or supporting documentation instead of guessing.
Look beyond the headline rating
A proposal should address load-based sizing, room airflow, humidity control, and commissioning. An efficiency upgrade that leaves a comfort problem unresolved may disappoint even if the equipment itself is good. Variable-output operation and other features can add comfort value, but evaluate those benefits separately from fuel-savings arithmetic.
Ask each bidder to state the rated combination, the efficiency premium, and the assumptions behind any savings claim. Read AC sizing limits and HSPF2 for heating before treating one efficiency number as a complete system assessment.