Evaporative Cooler vs Air Conditioner
Updated 2026-08-15 · 6 min read
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These are fundamentally different machines that both make a room cooler, and the deciding factor is your climate — not preference, budget, or unit quality.
How does an evaporative cooler differ from an air conditioner?
Air conditioner. A refrigeration cycle. A compressor circulates refrigerant that absorbs heat indoors and rejects it outdoors. It removes both heat and moisture, and works in any humidity.
Evaporative cooler (swamp cooler). A fan pulls outdoor air through water-saturated pads. Water evaporates, which absorbs heat from the air, and the cooled air is blown into the house. No compressor, no refrigerant.
The energy for that evaporation comes from the air itself, which is why the air comes out cooler — and more humid.
Why humidity decides everything
Evaporation requires air that can accept more moisture. Air that's already near saturation can't.
The physical limit is the wet-bulb temperature — the lowest temperature achievable by evaporation, determined by air temperature and humidity together. Real coolers reach part of the way toward it, typically a substantial fraction.
The consequence:
| Conditions | Evaporative cooling |
|---|---|
| 100°F, 15% humidity | Large temperature drop — genuinely effective |
| 95°F, 30% humidity | Useful drop |
| 90°F, 50% humidity | Small drop, and the added moisture offsets it |
| 90°F, 70% humidity | Essentially nothing, and it feels worse |
In dry air the effect is dramatic. In humid air you have an expensive fan that makes the room damp.
This is why swamp coolers are common in Phoenix, Albuquerque, and Denver, and absent in Houston, Atlanta, and Miami. It's geography, not marketing.
Side by side
| Evaporative cooler | Air conditioner | |
|---|---|---|
| Works in humid climates | No | Yes |
| Effect on indoor humidity | Increases it | Decreases it |
| Running cost | Much lower | Higher |
| Windows | Must be open | Must be closed |
| Water use | Continuous | None |
| Maintenance | Pads, water system, mineral scale | Filters, coils, refrigerant |
| Refrigerant | None | Yes |
| Filtration | Introduces outdoor air | Filters recirculated air |
The open-window requirement
This surprises people and it's not optional.
A swamp cooler continuously pushes outdoor air into the house. That air has to leave, or the house pressurizes and humidity climbs until cooling stops.
So you run a swamp cooler with windows cracked, typically on the side away from the unit, to establish a through-flow. Closing everything up — the correct move with an air conditioner — makes a swamp cooler stop working.
Practically, this means you can't use both systems in the same house at the same time, and it means the house isn't sealed against outdoor dust, pollen, or smoke.
Maintenance differences
Evaporative coolers need more frequent attention, of a different kind:
- Pads replaced periodically — they clog with mineral deposits and degrade
- Mineral scale management, worse with hard water; some units have a bleed-off to control it
- Water system cleaning to prevent biological growth in standing water
- Winterization — draining and covering the unit, since water in the system will freeze
That last item matters: an evaporative cooler is a seasonal appliance requiring shutdown and startup each year.
Running cost
The compressor is the large electrical load in an air conditioner. An evaporative cooler has a fan and a small water pump, and nothing else.
The energy difference is dramatic — but so is the applicability. A swamp cooler that doesn't work in your climate isn't cheap, it's useless.
There's also water use, which is continuous while running. In the arid regions where these work best, that's a real consideration and in some places a regulated one.
Estimate either with the electricity cost calculator.
"Ventless air conditioners"
Products sold as ventless air conditioners or personal air coolers are evaporative coolers, marketed misleadingly.
The physics is unavoidable: any real air conditioner must reject heat outdoors. A device with no exhaust to outdoors cannot be one. Small personal coolers work on the same evaporative principle, at small scale, with the same humidity dependence.
If a product claims to air-condition a room with no window venting and no outdoor unit, it's an evaporative cooler. See portable air conditioners explained.
Two-stage and hybrid
Two-stage evaporative coolers pre-cool the air before it reaches the wet pads, achieving lower temperatures with less added humidity. More effective, more expensive, still climate-dependent.
Hybrid setups run evaporative cooling during dry periods and switch to refrigerated air during monsoon season — common in the Southwest, where the climate does both.
The short answer
Dry climate: an evaporative cooler is genuinely excellent and costs far less to run.
Humid climate: it will disappoint you, and no amount of capacity fixes that.
Mixed climate with a wet season: consider both, or accept a compromise for part of the year.
Where to go next
More in our heating and cooling guides.
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