What Is a Swamp Cooler? How It Cools Dry Air

Check the air before choosing the cooler

If you're weighing one for your home, we'd look at your climate before comparing units, because humidity limits how much water can evaporate. A hot afternoon supplies only part of what the cooler needs. Dry air is the other part, and it makes the difference between useful cooling and adding moisture to an already humid space.

You might also see these appliances called desert coolers or wet air coolers. Those names describe the same basic cooling approach, so focus on the way the appliance works and the conditions it needs when you're comparing descriptions.

Where the heat goes

Turning liquid water into vapor takes energy. In an evaporative cooler, that energy comes from heat in the passing air. As water evaporates, the air loses heat and its temperature drops, which is why the appliance can deliver air that's cooler than the air entering it.

You've experienced the same principle when sweat evaporates from your skin. Evaporation takes heat from your body and helps you cool down. Inside the appliance, the wet cooling surface supplies the water, and the moving air supplies the heat needed for evaporation.

The result has two parts you need to consider together: a lower air temperature and more moisture in that air. The water becomes vapor as the air crosses the wet material. For Honeywell evaporative air coolers, that added moisture raises the surrounding humidity rather than being sprayed into the room as a mist.

What the fan, pump and pads each do

Follow the air through the appliance and the components make more sense. A fan draws warm, dry air through a wet pad, also called the cooling medium. A water tank or reservoir holds the water, and a pump supplies the wet medium so it can absorb and retain that water.

The pad gives water more surface area in contact with the passing air. That contact encourages evaporation and improves the cooling effect. The fan then sends the cooled air out the other side, carrying the water vapor with it.

Honeywell evaporative air coolers use honeycomb cooling media. Its increased surface area helps moisture transfer into the air moving through it. That detail explains why the material inside the cooler matters: the fan moves the air, while the wet medium provides the contact between air and water that makes evaporative cooling possible.

Why humid weather changes the result

Air that already contains plenty of moisture allows less water to evaporate. With less evaporation, there's less cooling. Hotter, drier incoming air gives a greater temperature drop than cooler, more humid incoming air, so the weather affects the temperature you feel at the outlet.

Very dry climates are the strongest fit. Evaporative cooling is unsuitable for much of the East Coast, Midwest and coastal United States. If you're considering it for your home, look at the humidity during the weather when you actually need cooling, alongside the temperature.

Comfort also depends on what happens to the moisture indoors. Outside very dry climates, an evaporative cooler can raise humidity enough to make people uncomfortable. For your buying decision, consider both the cooling available from the incoming air and how comfortable you'll be with added humidity in the room.

How to read cooling claims

A temperature-drop claim needs its temperature and humidity conditions attached. The air entering the cooler sets the opportunity for evaporation, while the cooling medium and the amount of air the appliance moves affect how much of that opportunity it can use.

A theoretical maximum is not a promise of the temperature you'll get at home; compare expected performance under your conditions and consider the unit's media and airflow. More efficient media helps a cooler get closer to its potential by exposing water to the passing air.

The amount of space the appliance can cool is another question. That depends on how much air it can move, with greater airflow supporting a larger cooled area. When you're comparing coolers, keep outlet temperature and coverage separate: one describes how cool the delivered air is, while the other concerns how much space the airflow can serve.

What changes with two-stage cooling

Evaporative cooling uses only a fraction of the energy used by traditional air conditioning systems. That makes it worth considering where the climate suits it, but the humidity effect remains part of the choice. Lower energy use and comfortable indoor conditions both matter.

A two-stage evaporative cooler changes how the air reaches the wet pad. First, air passes inside a heat exchanger that's cooled by evaporation on the outside. This first stage cools the incoming air indirectly, without adding moisture to it.

Next, the precooled air crosses a water-soaked pad and gains moisture as it cools further. Because the air is already cooler when it reaches that pad, less humidity is added than in a traditional single-stage system. Two-stage cooling changes the moisture tradeoff, while the overall suitability of evaporative cooling still depends on location and application.

Give indoor air a way out

For indoor use, open a window or door to let warm room air escape as cooled air arrives. Keep that exhaust path available while the cooler is in use. Without adequate exhaust, pressure and humidity build up, and oversaturation can leave the room feeling clammy.

Think about the route through the space, too. The opening's location helps guide air through the area you want cooled. An exhaust opening far from the cooled-air inlet lets air travel through that area before leaving the building.

This is why the room's exit for air belongs in your cooling plan alongside the appliance itself. The cooler needs a continuing path through the space, with incoming cooled air replacing air that leaves. Look from the cooled-air inlet toward your chosen open window or door and check that you've provided that exit.