What cooling actually costs
Central air conditioning, US average
$421a season
2,295 kWh · 2125 W average draw while running
Calibrated against the EIA survey mean of 2,318 kWh for households that run air conditioning. Your own figure depends more on climate than on equipment.
EIA RECS 2020, among households that run air conditioning, at 18.34¢/kWh.
| Census division | Cooling a year | Cost |
|---|---|---|
| West South Central | 3,873 kWh | $710 |
| South Atlantic | 3,112 kWh | $571 |
| Mountain | 2,918 kWh | $535 |
| East South Central | 2,812 kWh | $516 |
| West North Central | 1,728 kWh | $317 |
| Pacific | 1,514 kWh | $278 |
| Middle Atlantic | 1,483 kWh | $272 |
| East North Central | 1,425 kWh | $261 |
| New England | 1,136 kWh | $208 |
The setpoint is most of the lever
Cooling energy scales with the difference between indoors and outdoors, so each degree you let the house rise is worth roughly 3–5% of the whole end use. Nothing else you can do without spending money comes close.
Applied to $421 a season, using the midpoint of the 3–5% rule.
| Raise the setpoint by | Energy saved | Saved a season | New cost |
|---|---|---|---|
| 1°F | 4% | $17 | $404 |
| 2°F | 8% | $34 | $387 |
| 3°F | 12% | $51 | $370 |
| 4°F | 16% | $67 | $354 |
| 5°F | 20% | $84 | $337 |
Which of the standard advice survives
| The advice | Verdict |
|---|---|
| Raise the thermostat a few degrees | Works. The largest free saving available, by a wide margin. |
| Use ceiling fans in occupied rooms | Works. Cheap, and it buys real setpoint. |
| Close blinds on sun-facing windows | Works. Solar gain through glass is a large share of the cooling load in summer. |
| Service the system, clean the filter | Works. A restricted filter lowers airflow across the coil and raises run time. |
| Close vents in unused rooms | Backfires on ducted systems. It raises static pressure, cuts airflow across the coil, and can cost more than it saves. |
| Set it much lower to cool faster | Does nothing. A thermostat is a switch, not a throttle. The system runs at one speed either way; you just overshoot. |
| Turn it off entirely when out all day | Usually works, in dry climates. In humid ones the recovery has to remove the moisture the house absorbed, which can cost more than coasting — a setback rather than off is safer. |
Humidity is half the load, and it is invisible
An air conditioner does two jobs: it lowers the air temperature, and it condenses water out of the air. In a humid climate the second job can be a third to a half of the total energy, and none of it shows on a thermometer. This is why the same setpoint feels different in Arizona and Florida, and why the same equipment costs so much more to run in one than the other.
Two practical consequences follow. An oversized system is worse than a correctly sized one, because it satisfies the thermostat quickly and shuts off before it has run long enough to remove much moisture — leaving a house that is cold and clammy. And switching cooling off entirely while out, in a humid climate, lets the building materials absorb moisture that the system must then remove on recovery, which can cost more than simply coasting at a higher setpoint.
What SEER actually buys you
SEER is cooling output divided by electrical input over a season, so it is a straightforward efficiency ratio: a SEER 20 unit uses about two thirds the electricity of a SEER 13 one for identical cooling. The saving is real and it is easy to compute.
Applied to $421 a season at 18.34¢/kWh. Divide the price difference by the annual saving for a payback in years.
| Replacing a SEER 13 system with | Energy used | Cost a season | Saved a season |
|---|---|---|---|
| SEER 14 | 93% | $391 | $30 |
| SEER 16 | 81% | $342 | $79 |
| SEER 18 | 72% | $304 | $117 |
| SEER 20 | 65% | $274 | $147 |
| SEER 22 | 59% | $249 | $172 |
The other summer loads people forget
At 18.34¢/kWh.
| Appliance | A season | Why summer |
|---|---|---|
| Pool pump | $396 | Single-speed pumps on a default eight-hour timer. A variable-speed replacement cuts this by around 70%. |
| Pool heater | $576 | Almost all of it is replacing evaporative loss from the surface. A cover is worth more than any efficiency setting. |
| Dehumidifier | $228 | Its waste heat stays in the room, so the air conditioning then removes it again. You pay twice. |
| Portable air conditioner | $141 | Single-hose designs exhaust conditioned air outdoors and pull hot air in through every gap to replace it. |
| Garage refrigerator | $130 | Works far harder in a hot garage than the same unit would indoors. |
Sizing, and why bigger is not better
An oversized air conditioner is a common and expensive mistake, and it is counter-intuitive enough to be worth stating plainly: a system with more capacity than the house needs will cool it worse and cost more. It reaches the setpoint quickly, shuts off, and never runs long enough to dehumidify properly — so the house feels cold and damp rather than comfortable. It also short-cycles, and starting a compressor is the hardest thing it does, so frequent starts shorten its life as well as wasting energy.
The symptom to look for is run time. A correctly sized system on a design-temperature day should run most of the time — 50 to 70% is normal and healthy. If yours runs for ten minutes and stops for twenty on the hottest afternoon of the year, it is too big for the house.
Questions
What temperature should I set my air conditioning to?
Is it cheaper to leave the AC on all day or turn it off?
Do ceiling fans actually save money?
Why is my portable air conditioner so expensive to run?
All guides · How the figures are computed · Break down your own bill