How to Choose an Evaporative (Swamp) Cooler

In a dry climate, an evaporative cooler can drop the air 15–30°F for a fraction of what an air conditioner costs to run. But that same machine is nearly useless in humid air — so the first question isn’t which model, it’s whether a swamp cooler fits your weather at all.

First, does your climate even qualify?

An evaporative cooler works by pulling warm, dry air through a wet pad. Water evaporates, the air gives up heat to do it, and what comes out the other side is cooler and more humid. That physics only pays off when the air is thirsty. As a rule of thumb, evaporative cooling shines below about 50% relative humidity and struggles above 60%. In Phoenix or Albuquerque in July it’s magic; in Houston or Atlanta it just makes a muggy room muggier.

Check your local afternoon humidity for the hottest months before you spend a dime. If the numbers are borderline or clearly humid, stop here — a good box, tower, or pedestal fan or a compressor-based unit from our portable AC and dehumidifier selection is the right tool. Swamp coolers reward the right climate and punish the wrong one.

Size it by CFM, not by guesswork

Coolers are rated in CFM — cubic feet per minute of air they move. The goal is to change the air in your space every couple of minutes. The standard formula: multiply the square footage by the ceiling height, then divide by two. A 400 sq ft room with 8’ ceilings needs about 1,600 CFM. In extreme dry heat, size up one bracket so the unit doesn’t run flat-out all day.

Tip: bigger isn’t automatically better. An oversized portable in a small closed room just raises humidity and dampens everything. Match the CFM to the space and keep a window cracked so moist air has somewhere to go.

Portable, window, or whole-house?

Portable coolers — the wheeled units from names like Hessaire, Honeywell, and NewAir — are the easy entry point. You fill a tank (or run a garden hose for continuous operation), plug into a standard outlet, and roll them where you need them. They’re ideal for a single room, a workshop, or a covered patio. Industrial “spot coolers” from Portacool are the same idea scaled up for garages and open worksites.

Window and whole-house units (Champion, Mastercool, and Frigidaire among them) mount permanently and cool the entire home through the duct network or an open floor plan. They cost more, need a plumbed water line and often roof or wall installation, but deliver dramatically lower running costs than central AC in dry climates. If a hose is your water source, a good-quality garden hose and a float-valve kit keep the reservoir topped without babysitting.

• Airflow (CFM): the single most important spec — size it to the room.
• Water capacity & hose hookup: a bigger tank means fewer refills; a hose inlet means none.
• Pad type: thick rigid-media (CELdek-style) pads cool better and last longer than thin aspen pads.
• Speed settings & oscillation: variable speed plus louvers spread the cool air.
• Pump-only / fan-only mode: lets you circulate air on already-humid evenings without wetting the pads.

Running costs and the maintenance reality

The headline is real: evaporative coolers use roughly a quarter of the electricity of a comparable air conditioner because there’s no compressor — just a fan and a small water pump. The trade-off is water use and upkeep. A whole-house unit can use 3–15 gallons an hour on the hottest days, and the pads, pump, and reservoir need attention.

Every season you’ll drain and clean the reservoir to prevent mineral scale and mold, replace or wash the pads, and check the pump and float valve. In hard-water regions, a bleed-off line or periodic descaling keeps mineral buildup from clogging the pads. This is genuinely lighter maintenance than it sounds — an afternoon in spring and a drain-down at season’s end — but it’s not zero. If you also fight dust and allergens, pairing the cooler with an air purifier handles the particulates the cooler’s pad won’t.

Get the most out of it

The counterintuitive rule with evaporative cooling: keep windows open. Unlike an AC, a swamp cooler needs a constant path for air to exit — crack windows on the far side of the space so cool air pushes through and moist air escapes. Two to four inches of total window opening per 1,000 CFM is a good starting point. Run it in the morning to get ahead of the heat, and use a thermometer or hygrometer to confirm the humidity indoors stays comfortable. Circulating the cooled air with ceiling fans lets you run the cooler on a lower speed and still feel the effect.

Pick by situation

Frequently asked questions

The right cooler comes down to your climate first and your square footage second — get those two right and the rest is easy. Want to see a unit run before you buy, or talk pads and hookups with someone who knows your local summers? Visit your local independent hardware store, or ask us here.