Traditional air conditioners—window units, central air, even those clunky portable units with the big unsightly hoses—are great tools for removing the heat from a room. Although using AC does effectively leave you feeling cooler than before, it’s also an energy-intensive process. Air conditioning costs money, and it also leads to a sort of self-fulfilling prophecy: All that energy use contributes to global warming, which means we need to use more air conditioning, which uses more energy, which costs more money, and so on forever. And that’s before we even get into the complicated contributions of chemical refrigerants.
Evaporative cooling (PDF) is a refrigerant-free alternative that uses much less energy. There are a lot of different ways to take advantage of natural evaporative processes, but one common solution is to build or buy an evaporative cooler. Also known as a swamp cooler, this device uses a fan to recirculate the room’s air across a cool, wet pad (aka a wick) and then expel that freshly dampened air into the room. You know those little spray bottles with the fan mounted on top that people use to spritz water in their faces while they’re waiting in line for a roller coaster in the dead of the summer? It’s basically that, on a larger scale.
But do these swamp coolers actually work? And if so, why isn’t everyone using them?
Evaporative cooling is loosely based on an ancient, time-honored process known as sweating. You may have heard of it. Our bodies automatically cool themselves down by releasing moisture through the skin; the moisture gets picked up by a pleasant breeze and brings us back down to a more comfortable temperature. A quick run through a sprinkler has the same effect. That’s essentially what a swamp cooler does to the air in a room. But, as we found in testing, your starting ambient environmental conditions play a huge part in how well this works to make you feel cooler.
We tested two portable commercial swamp coolers, the Frigidaire EC200WF and the Frigidaire EC300W-FA, against our portable air conditioner picks to see how they stacked up. Slowly but surely, the swamps did cool the room, though not nearly as well as the (famously inefficient) portable ACs. But for every 1 degree swamp coolers dropped the temperature in the room, they also added about 2% to 3% to the humidity. On a very technical level, this makes sense; after all, it is what they’re designed to do. By contrast, portable and window air conditioners actually de-humidify a space as part of their cooling process, and we saw that in our tests as well (that’s also why that second-floor window AC is always dripping on you). Both methods can help keep you cool; they just use different approaches to achieve that.
But in a testing environment like the one we were using—in the coastal Northeast, on a day when the humidity outside was already above 50%—we were essentially setting these swamp coolers up to fail. With the air as saturated as it was, the machines couldn’t do much except over-humidify the room, making it danker without any significant cooling or comfort. It was the same unpleasant feeling you get when your sweat won’t evaporate on a muggy day. In a drier environment, however, humidifying the air as it passed through a fan could have made a serious difference. According to the US Department of Energy (DOE), an evaporative cooler can successfully reduce the ambient temperature by 5 to 15 degrees—but even the DOE is quick to clarify that this process works only in areas with low humidity.
In other words, a swamp cooler isn’t a great choice for a place like Boston (where we ran our initial tests). But if you live in a warm, arid climate, particularly in the western US, it can be a reliable and cost-effective way to bring some chill into your summer. One Amazon reviewer based in Arizona gave five stars to the Frigidaire EC300W-FA we tested, saying that “an extra bonus for me is that I can take it into my workshop or put it next to me on my porch—places where an air conditioner wouldn’t work.” Another reviewer said that although the Frigidaire EC300W-FA dropped the temperature by a few degrees, “it also increased the relative humidity in the room from 13% to 40%.” There are plenty of other reviewers, in places like Las Vegas and Boise, Idaho, who also talked up the cooling sensation they got from their swamp coolers, while also acknowledging that a cool feeling is not always the same as actual air conditioning.
If you want to save even more money—and you’re feeling crafty—you can also fashion your own swamp cooler using a 5-gallon bucket (video), a Styrofoam cooler (video), or even an old computer fan in an empty milk carton (video). These DIY evaporative cooler projects all rely on the same basic parts: an electric fan, a container or pump to provide the water, and a wick or aquarium tube to carry the water to the fan. You may need some basic tools for cutting, and some of these MacGyvered swamp coolers recommend using additional piping to keep the airflow going strong. But in the right climate, an hour of work and a hundred bucks could get you a decent alternative to buying a whole new air conditioner. One DIYer even said his homemade swamp cooler “takes a while to cool a whole room, but it lowers my room average from 25 °C [77 °F] to 16 °C [60.8 °F] through the day.”
But, of course, time is money, and it might be easier to buy a premade swamp cooler. The Frigidaire EC200WF we tested will cost you only about $80 more than a homemade model. And for about $70 on top of that, the larger Frigidaire EC300W-FA will give you nearly three times the tank size and nearly twice the fan power. The EC300W-FA can also be used outdoors to add a gentle misting breeze to your patio. Even in the worst-case scenario, you can still use any swamp cooler as a giant fan. And on a hot summer day, that’s better than nothing.
It’s Chill Week at Wirecutter! Read more about ways to cool down and get the most out of summer.