An evaporative cooler is a device that cools air by pulling it through water-soaked pads, dropping the temperature through evaporation.
If you’ve ever stood in front of a fan while spraying yourself with water, you already understand the principle behind an evaporative cooler. Unlike standard air conditioners that use refrigerants and compressors, these units use plain water and moving air. The warm air passes through saturated pads, water evaporates, and the air temperature drops noticeably — but only under the right conditions. The U.S. Environmental Protection Agency notes these systems are sometimes called “swamp coolers” or “whole-house evaporative coolers.”
How Does an Evaporative Cooler Work?
An evaporative cooler draws warm outdoor air through water-saturated evaporative media — usually cellulose or synthetic pads — and a fan pushes the cooled air into your living space. As the water evaporates from the pads, it absorbs heat from the air, lowering the temperature. The cooled air then needs somewhere to go, which is why proper ventilation and relief air are essential.
The effectiveness depends on a simple environmental factor: humidity. Dry air absorbs water vapor readily, so cooling is dramatic in arid climates. As outdoor humidity rises, evaporation slows and performance drops. This is why the Department of Energy’s guidance frames evaporative cooling as appropriate primarily for dry climates, with suitability based on local wet-bulb temperatures.
Official federal specifications for packaged evaporative air coolers describe a weatherproof metal cabinet containing three core components: a fan, evaporative media, and a water distribution system. That’s the entire machine — no compressor, no chemical refrigerant, just airflow and water.
What Size Evaporative Cooler Do You Need?
You need enough airflow — measured in cubic feet per minute (CFM) — to exchange the room’s air roughly 30 times per hour.
Beyond raw airflow, the sizing process includes checking local climate suitability, considering maintenance access, plumbing and electrical hookups, and ducting requirements.
Commercial units span a wide range. One manufacturer sheet lists models from 2,000 CFM to 16,000 CFM, with 304 stainless steel housings and 12-inch rigid cooling media. Seeley’s Breezair line offers residential models like the TBQI and EXVQ with 5,500–7,500 CFM and variable-speed inverter motors for quieter operation.
When Should You Not Use a Swamp Cooler?
Evaporative coolers are the wrong tool in humid climates and the wrong tool in sealed spaces. The EPA advises against using one when outdoor pollution is high unless the unit has a high-efficiency filter. Since the cooler pulls air from outside and pushes it into your home, that air brings outdoor particles with it.
Indoor use carries one absolute rule: never operate the unit in an enclosed or sealed room. Evaporative coolers add significant moisture to the air and require a continuous supply of fresh air and a path for exhaust. Without relief air, humidity climbs, cooling efficiency collapses, and indoor air quality degrades. That same moisture is why maintenance access matters — PNNL guidance highlights regular pad replacement, water distribution checks, and off-season protection with a cover.
Energy Use and Cost Considerations
The honest comparison: evaporative coolers typically use far less electricity than refrigerant-based AC because the only significant load is the fan and a small water pump. For homes in dry western states, the savings can be substantial. But the trade-off is real — performance varies with weather, and on humid days the unit simply cannot deliver the same temperature drop.
If you’re weighing an evaporative cooler against a traditional AC, your local climate is the deciding factor. The EPA and PNNL both anchor their guidance on wet-bulb temperature, which measures how much moisture the air can still absorb. The drier your climate, the better an evaporative cooler will perform.
When you’re ready to compare specific models, our tested roundup of the best AC evaporative coolers covers performance, coverage, and value across top options.
References & Sources
- U.S. Environmental Protection Agency. “Will Running an Evaporative Cooler, Sometimes Known as a Swamp Cooler or Whole-House Cooler, Help Cool the House?” Explains operating principles, dry-climate suitability, and air quality caveats.
- Pacific Northwest National Laboratory. “Evaporative Cooling Systems Resource Guide.” Provides sizing calculations, installation guidance, and maintenance requirements.
FAQs
Are evaporative coolers effective in humid climates?
No. Evaporative cooling works by evaporating water into the air, and humid air already holds significant moisture. As humidity rises, evaporation slows and cooling performance drops sharply. These units are designed for dry climates where wet-bulb temperatures are low, typically the western United States and other arid regions.
Do evaporative coolers use less electricity than air conditioners?
Yes, in most cases. An evaporative cooler runs only a fan and a water pump, avoiding the compressor found in refrigerant-based AC systems. That means noticeably lower energy consumption and lower utility bills, though the savings depend on how often the unit runs and local electricity rates.
Can you run an evaporative cooler with the windows closed?
No. Evaporative coolers need a path for relief air to escape. Sealed spaces trap humidity, which stops evaporation and makes the cooler ineffective. Always provide adequate ventilation, typically an open window, so moist air can leave and dry outdoor air can enter.