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Climate decides this, not price. An evaporative cooler (swamp cooler) cools by evaporating water into the air, so it only works where the air is dry — and it adds humidity to the room. An air conditioner moves heat out with a refrigerant loop, works in any humidity, and takes moisture out. In the desert Southwest the cooler wins decisively on running cost, drawing roughly 100 to 300 watts against 1,000 to 1,400 watts for a portable AC. In the humid Southeast the cooler is simply the wrong machine.
We never buy, test or physically handle the products we rank; recommendations come from aggregated owner reviews and expert consensus, described in how we rank. More at the heating & cooling hub.
How the two machines actually work
They are not two grades of the same thing, which is why the comparison is not a simple better-or-worse.
An evaporative cooler pulls warm dry outside or room air through a wet pad. Some of the water evaporates, and evaporation absorbs heat from the air, so the air comes out cooler and more humid. There is no refrigerant and no compressor — just a fan, a pump and a wet pad. The limit on how cold the air can get is the wet-bulb temperature of the incoming air, which is a function of its temperature and humidity. That is why the machine's performance is set by your climate rather than by its price.
An air conditioner uses a refrigerant loop to move heat from inside to outside. Air passing over a cold evaporator coil both cools and loses moisture, because water condenses out of it. It works regardless of the outside humidity, and it dehumidifies as a side effect — which in a muggy climate is half the reason it makes a room comfortable.
The numbers side by side
| Evaporative cooler | Portable air conditioner | |
|---|---|---|
| Works in humid air | No | Yes |
| Effect on room humidity | Raises it | Lowers it |
| Typical power draw | 100–300 W | 1,000–1,400 W for 10,000 BTU |
| Cost per 8 hours at ~17¢/kWh | ~$0.15–$0.40 | ~$1.40–$1.90 |
| Purchase price | $130–$400 | $350–$700 |
| Temperature drop delivered | 15–40°F in supply air, humidity dependent | Set point independent of outside humidity |
| Needs a window | Yes — as an open relief path | Yes — for the exhaust hose |
| Works in a sealed room | No, by design | Yes (window or split units best) |
| Water | Consumes water; reservoir needs cleaning | Produces condensate to drain |
| Noise | Fan noise, often significant on high | Compressor cycling plus fan |
| Outdoor use | Works well on a covered patio | Pointless outdoors |
The supply-air figures come from the Department of Energy's Building America Solution Center, which puts an evaporative cooler's temperature reduction at "15°F to 40°F" depending on humidity and equipment, with modern pads reaching "cooling effectiveness of 75% to 93%." The electricity cost figures use a national average price of roughly 17 cents per kWh; check your own rate, which may be well above or below that.
How much does humidity change the answer?
Enough that it is the only question that really matters. The same DOE source gives a worked example: at 100°F outdoors with 10% relative humidity, supply air comes out at about 73°F — a 27-degree drop. At 95°F with 50% relative humidity, the same equipment only reaches 84°F — an 11-degree drop. Identical machine, less than half the benefit, and in the second case it is also pushing moisture into a room that already has plenty.
The technical threshold is wet-bulb temperature. DOE guidance is that "areas with wet-bulb temperatures of 70°F or lower are appropriate for evaporative cooling," with function up to about 74°F wet-bulb and reduced performance. At 100% relative humidity, "evaporative cooling cannot occur" at all, because there is no capacity left in the air to absorb water.
| Where you live | Evaporative cooler | Air conditioner |
|---|---|---|
| Phoenix, Las Vegas, Tucson, El Paso | Excellent — the obvious choice for garages and open areas | Better for sealed bedrooms |
| Albuquerque, Denver, Salt Lake City, Boise | Very good | Optional |
| Spokane, Yakima, Bend, inland CA valleys | Good | Optional |
| Denver to Dallas corridor, Oklahoma, Kansas | Works on dry days, poor on muggy ones | The safer buy |
| Chicago, St. Louis, Nashville, Charlotte | Not recommended | Yes |
| Houston, New Orleans, Tampa, Charleston | No — it will add humidity and not cool | The only sensible option |
The airflow requirement people miss
An evaporative cooler is not a closed-loop device. It pushes a continuous stream of humid, cooled air into the space, and that air has to get out — otherwise the room's humidity climbs until evaporation stops and the cooling stops with it. DOE guidance specifies about 2 square feet of unrestricted air relief for every 1,000 CFM of delivery, and 20 to 40 air changes per hour through the conditioned space.
In practice, a 3,100 CFM unit needs more than 6 square feet of open window — roughly a 2.5-foot square — and that window should be on the far side of the room so the air crosses the space. If you cannot do that, the machine will humidify rather than cool, and every review saying "it just made my room muggy" is describing exactly this.
A portable air conditioner has its own airflow catch. Single-hose units exhaust hot air out of the window but must draw replacement air from somewhere, and that somewhere is the rest of your house — including any warm outdoor air leaking in to replace it. Dual-hose units avoid this and are meaningfully more effective, which we cover in single vs dual hose portable air conditioners.
Running cost over a real summer
Take a garage cooled eight hours a day for 100 days of a desert summer. An evaporative cooler at 200 watts uses about 160 kWh over that period, which is around $27 at 17 cents per kWh. A 10,000 BTU portable air conditioner at 1,200 watts uses about 960 kWh, around $163. That gap — well over $100 in a single season, in one room — is the honest reason evaporative cooling became standard equipment across the dry states rather than a niche curiosity.
Two costs on the other side of the ledger. The cooler consumes water: DOE figures for a 1,500 square foot home in New Mexico range from 2,980 gallons a year in Santa Fe to 12,457 in Las Cruces, and 50% more if the unit has a bleed-off valve. And the cooler needs seasonal cleaning and pad replacement, which an air conditioner does not, beyond a filter. Neither changes the conclusion in a dry climate, but they should be in the calculation. Our water use page works through the gallons in detail, and the appliance running cost calculator lets you run your own electricity rate.
Health and comfort differences
These are different in kind, not just degree, and they cut both ways.
The cooler adds humidity, which in genuinely dry air is a comfort benefit — dry sinuses, static and cracking wood trim are real complaints in the desert. In air that is already humid, added moisture makes conditions feel worse at the same temperature, and sustained high indoor humidity encourages mold growth.
The cooler holds standing water. DOE guidance notes that "standing water left in the pan can become a breeding ground for mosquitos and bacteria, including Legionella (the cause of Legionnaires' Disease)," and recommends maintenance at least twice a year. The habit that prevents it is draining the pan whenever the unit sits idle. An air conditioner produces condensate rather than storing it, so the equivalent risk is much lower — though a portable AC's condensate tray still needs emptying and its filter still needs cleaning.
The cooler continually brings in outside air, which is good for indoor air quality and bad on a wildfire smoke day or during a high pollen count. An air conditioner recirculates through a filter, which is the better setup when outdoor air quality is poor.
So which should you buy?
- Dry climate, garage or shop or covered patio: evaporative cooler, comfortably. Cheap to run, no window kit, and opening the space up is easy. See our swamp cooler picks, where the Hessaire MC37M (paid link) is the unit with the deepest ownership record.
- Dry climate, bedroom you want closed at night: air conditioner, because the cooler's open-window requirement defeats the purpose.
- Humid climate, anything: air conditioner. See our portable AC picks and bedroom portable AC picks.
- Mixed climate: air conditioner if you are only buying one, since it works on the humid days too. A cooler with a fan-only mode is a reasonable second unit for a garage.
- Tight budget, dry climate: the smaller Hessaire MC18M (paid link) is the cheapest route to a genuinely cooler room, and it is the quietest unit in that category.
- Neither, yet: in many houses the biggest available gain is shading the windows and flushing hot air at night. Our cooling without AC guide covers it, and it costs nothing.
The honest bottom line
In dry air, an evaporative cooler is one of the best value propositions in home cooling: a 20-degree-plus drop in supply air for a tenth of the electricity, in a machine that costs half as much. In humid air it is the wrong tool, and no feature list changes that — it will add moisture to a room it cannot cool. Check whether your summer wet-bulb temperature sits at or below about 70°F, decide whether you can leave a window genuinely open, and let those two answers pick the machine.
More from this hub: heating & cooling · best evaporative coolers · do evaporative coolers work in humidity · portable AC vs window AC · how we rank.