The SEER formula is: SEER = Total Cooling Output (BTU) divided by Total Electrical Energy Input (Wh) over a full cooling season. For practical purposes, you can estimate your annual cooling cost using: Annual Cost = (Cooling Capacity x Cooling Hours) / (SEER x 1,000) x Electricity Rate. A 3-ton, 16 SEER AC running 1,500 hours at $0.16/kWh costs approximately $540 per year to operate.
This guide walks through the SEER formula step by step, shows you how to calculate cooling costs, and provides worked examples so you can compare any two AC units on an equal basis.
The Basic SEER Formula
SEER = Total Cooling Output (BTU) / Total Electrical Input (Wh)
Both values are measured over an entire standardized cooling season. In lab testing, this involves running the system across eight temperature bins from 65 to 104 degrees F, weighted by the typical hours at each temperature.
You won't do this lab test yourself. Instead, you'll use the published SEER or SEER2 rating to calculate practical things like energy costs and savings.
Formula 1: Estimate Annual Cooling kWh
Annual kWh = (Cooling Capacity BTU/h x Annual Cooling Hours) / (SEER x 1,000)
This formula tells you how many kilowatt-hours your AC uses per year for cooling.
Example: A 3-ton AC (36,000 BTU/h) rated at 16 SEER runs for 1,500 hours per year.
Annual kWh = (36,000 x 1,500) / (16 x 1,000) = 54,000,000 / 16,000 = 3,375 kWh
Tonnage to BTU/h Conversion
Formula 2: Estimate Annual Cooling Cost
Annual Cost = Annual kWh x Electricity Rate ($/kWh)
Or combined into one formula:
Annual Cost = (BTU/h x Hours) / (SEER x 1,000) x $/kWh
Example: Same 3-ton, 16 SEER unit, 1,500 hours, at $0.16/kWh.
Annual Cost = 3,375 kWh x $0.16 = $540
Formula 3: Calculate Savings Between Two Units
Annual Savings = Annual Cost (Old Unit) - Annual Cost (New Unit)
Or directly:
Annual Savings = (BTU/h x Hours x $/kWh) x (1/SEER_old - 1/SEER_new) / 1,000
Example: Upgrading from 12 SEER to 18 SEER. 3-ton, 1,500 hours, $0.16/kWh.
Old cost: (36,000 x 1,500) / (12 x 1,000) x $0.16 = $720/year
New cost: (36,000 x 1,500) / (18 x 1,000) x $0.16 = $480/year
Annual savings: $720 - $480 = $240/year
Or using the direct formula: Savings = (36,000 x 1,500 x 0.16) x (1/12 - 1/18) / 1,000 = 8,640 x (0.0833 - 0.0556) = 8,640 x 0.0278 = $240/year
Formula 4: Simple Payback Period
Payback (years) = Additional Cost of Higher-SEER Unit / Annual Savings
Example: The 18 SEER unit costs $2,000 more than the 12 SEER unit.
Payback = $2,000 / $240 = 8.3 years
If you factor in a $600 tax credit: Payback = ($2,000 - $600) / $240 = 5.8 years
Formula 5: Convert Between SEER and SEER2
SEER2 = SEER / 1.047
SEER = SEER2 x 1.047
Example: Your old AC is rated 16 SEER. What's the SEER2 equivalent?
SEER2 = 16 / 1.047 = 15.3 SEER2
A new 15.3 SEER2 unit is approximately equivalent in efficiency to your old 16 SEER unit.
Formula 6: Convert SEER to COP
COP = SEER / 3.412
This gives you the seasonal average COP for cooling.
Example: An 18 SEER unit.
COP = 18 / 3.412 = 5.27
This means the unit delivers 5.27 BTU of cooling per BTU of electrical input on average over the season. (This sounds incredibly efficient because SEER heavily weights mild-weather performance.)
Complete Worked Examples
Example A: Florida Homeowner
You live in Tampa, FL. 4-ton system, 2,500 cooling hours, $0.15/kWh. Comparing 14.3 SEER2 vs 20 SEER2.
14.3 SEER2 cost: (48,000 x 2,500) / (14.3 x 1,000) x $0.15 = 8,392 kWh x $0.15 = $1,259/year
20 SEER2 cost: (48,000 x 2,500) / (20 x 1,000) x $0.15 = 6,000 kWh x $0.15 = $900/year
Annual savings: $359. 15-year savings: $5,385.
Example B: Minnesota Homeowner
You live in Minneapolis. 3-ton system, 800 cooling hours, $0.14/kWh. Comparing 13.4 SEER2 vs 16 SEER2.
13.4 SEER2 cost: (36,000 x 800) / (13.4 x 1,000) x $0.14 = 2,149 kWh x $0.14 = $301/year
16 SEER2 cost: (36,000 x 800) / (16 x 1,000) x $0.14 = 1,800 kWh x $0.14 = $252/year
Annual savings: $49. 15-year savings: $735.
Example C: Comparing Old System to New
Your 15-year-old system is rated 10 SEER. You're considering a new 18 SEER2 unit. 3-ton, 1,500 hours, $0.16/kWh.
First convert old SEER to SEER2 for apples-to-apples: 10 / 1.047 = 9.6 SEER2 equivalent.
Old system cost (9.6 SEER2 equivalent): (36,000 x 1,500) / (9.6 x 1,000) x $0.16 = $900/year
New 18 SEER2 cost: (36,000 x 1,500) / (18 x 1,000) x $0.16 = $480/year
Annual savings: $420. 15-year savings: $6,300.
Your old system may perform below its rated SEER. After 15 years, dirty coils, low refrigerant, and worn components can reduce actual efficiency by 10-20%. Your real savings from replacing an old unit may be even higher than these calculations suggest.
SEER2 Savings Calculator
Use this interactive calculator for instant comparisons:
Key Takeaways
- Core formula: SEER = Total BTU Output / Total Wh Input over a full cooling season
- Annual cost = (BTU/h x Hours) / (SEER x 1,000) x $/kWh
- Savings = Old Cost - New Cost using the formula for each SEER rating
- Payback = Extra Cost / Annual Savings (subtract tax credits from extra cost)
- SEER to SEER2: divide by 1.047. SEER2 to SEER: multiply by 1.047.
- SEER to COP: divide by 3.412 for the seasonal cooling efficiency ratio
- Key variables: system size (tons), cooling hours, electricity rate, and SEER rating. Change any of these and the economics shift.
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