Air Conditioner Running Cost Calculator
Enter your unit's size and efficiency. The calculator handles duty cycle, which is why a 3-ton unit doesn't cost anywhere near what its nameplate wattage suggests.
How this is calculated
SEER is cooling output per unit of electricity, so power draw follows directly:
watts = BTU/h capacity ÷ SEER
kWh = (watts ÷ 1000) × hours × days × duty cycle
A 36,000 BTU unit at SEER 14 draws about 2,571W while the compressor runs — but it does not run continuously, which is what duty cycle captures.
Duty cycle: why nameplate wattage misleads
Air conditioners cycle. On a mild day a correctly sized unit might run 40% of the time; in a heatwave, 85%. That range more than doubles the cost for the same equipment and thermostat setting.
| Conditions | Duty cycle | Season cost |
|---|---|---|
| Mild summer, well insulated | 40% | $216 |
| Typical summer | 60% | $323 |
| Hot climate | 75% | $404 |
| Extreme heat / undersized unit | 90% | $485 |
36,000 BTU, SEER 14, 8 h/day, 120 days, $0.1745/kWh.
Does a SEER upgrade pay for itself?
Only if you cool enough hours. The saving is proportional to runtime, so the same upgrade can be excellent in Phoenix and pointless in Portland.
| Upgrade | Season saving | Cost | Payback |
|---|---|---|---|
| SEER 10 → 14 | $129 | ~$1,500 | 12 yrs |
| SEER 14 → 18 | $72 | ~$2,000 | 28 yrs |
| SEER 14 → 18, hot climate | $215 | ~$2,000 | 9 yrs |
Practical read: upgrade SEER when you are replacing a unit anyway, not as a standalone project. Replacing a working SEER 14 unit with a SEER 20 rarely repays before the new unit needs replacing itself.
What actually cuts cooling bills
- Raise the thermostat. Each degree saves 3–5%. Free.
- Seal duct leaks. Typical homes lose 20–30% of conditioned air through ducts. Often the highest-return fix available.
- Change the filter. A clogged filter makes the unit run longer for the same cooling.
- Shade windows. Solar gain through glass is a large share of cooling load.
- Use fans. Moving air makes a room feel 4°F cooler for a fraction of the electricity.
Related
- Appliance running cost
- Heat pump vs furnace — a heat pump cools too
Common questions
What is SEER and does a higher number pay for itself?
SEER is cooling output in BTU divided by electricity input in watt-hours across a season. Higher is more efficient. Going from SEER 13 to SEER 20 cuts running cost by about 35%, but the upgrade often costs $2,000–4,000. In a hot climate running 1,500 hours a year that can repay in 5–8 years; in a mild climate running 300 hours it may never repay. Cooling hours decide it.
Is it cheaper to leave the AC on all day or turn it off?
Turning it off is cheaper, contrary to a persistent myth. An air conditioner does not work harder to cool a hot house than it does maintaining a cool one — it simply runs longer. Heat flows into your home in proportion to the indoor-outdoor temperature difference, so letting the house warm while you are out reduces total heat gain. A programmable thermostat that cools before you return captures the saving without the discomfort.
How much does each degree cost me?
Roughly 3–5% of cooling cost per degree Fahrenheit. Moving from 72°F to 76°F typically cuts cooling costs 12–20% — often $80–150 across a summer. It is the cheapest efficiency measure available, requiring no purchase at all.
Why is my bill higher than this estimate?
Usually duty cycle. In a serious heatwave a unit can run 80–90% of the time rather than the 50–60% typical of an average day. Undersized units, poor insulation, leaky ducts and dirty filters all push runtime up. Try raising the duty cycle to see the heatwave scenario.