The Best Climates for Swamp Coolers, Region by Region

The best climates for swamp coolers are hot enough to need cooling and dry enough that evaporation does the job. In the US that is a well-defined belt: the Mountain West and Great Basin, the Colorado Plateau and Front Range, the deserts of Nevada, Arizona, New Mexico and far West Texas, and the inland valleys of California. The single best predictor is the summer wet bulb temperature. Below about 68 F on hot afternoons, a cooler can be your only cooling system. Above about 75 F, it becomes a fan that adds moisture.

How to rate a climate for evaporative cooling

Engineers use ASHRAE climatic design data, which lists for each weather station a design dry bulb (exceeded only about 1% of summer hours) and the mean coincident wet bulb at that temperature. From those two numbers you can predict what a cooler will deliver on a typical hot afternoon:

We use 88% efficiency (8 in rigid media) below, with the same rating rules as our climate index: a supply temperature of 70 F or less is excellent, 70 to 74 F good, 74 to 78 F marginal and above 78 F poor. Cities with a design wet bulb of 72 F or more rate no better than marginal, and 75 F or more rate poor, because indoor humidity runs high.

A second number matters for monsoon-affected places: the separate design wet bulb (the wet bulb exceeded 1% of hours). In dry climates it is only a few degrees above the coincident wet bulb. In monsoon climates it can be 5 F or more higher, which tells you there are humid stretches when cooling falls off.

Predicted cooler performance in 15 US cities

Design values are rounded approximations of published ASHRAE data and vary by station and edition. Dallas and Atlanta show how a high wet bulb caps the rating: humid hours are long and frequent, so indoor humidity would run high even when the supply temperature looks tolerable. Our climate index covers 50 cities with achievable supply temperatures.

The regional tiers

Tier 1: excellent, a cooler can be your only system

The Front Range and Western Slope of Colorado, the Wasatch Front and most of Utah, the Reno and Carson City area, southern and western Idaho, high-desert New Mexico (Albuquerque, Santa Fe), northern Arizona below the mountains, eastern Oregon and Washington, and much of Wyoming and Montana's lower valleys. Elevations of 4,000 to 6,000 ft, cool nights and dew points that seldom rise above the 50s F make these ideal. Many homes here never install AC.

Tier 2: very good, with occasional humid spells

Las Vegas, St. George, the high desert of Southern California (Victorville, Lancaster), Bakersfield and the southern Central Valley, Grand Junction, El Paso. Hot and dry for most of summer. Some years bring humid surges that make a few weeks marginal.

Tier 3: strong but seasonal

Phoenix, Tucson, Yuma, the Coachella Valley, the Inland Empire, Sacramento and Fresno. Excellent from April through June. The Arizona monsoon (typically July to mid September) or occasional tropical moisture reduces performance for weeks at a time. Dual systems (cooler plus AC) are common and sensible here; see swamp coolers during monsoon season.

Tier 4: limited or spot use only

West Texas Panhandle, western Kansas and Oklahoma, eastern Colorado plains, and much of the Dakotas and Nebraska west of about the 100th meridian. Dry on many days, but Gulf moisture moves in frequently. Coolers work for shops, garages and barns where airflow matters most; see swamp cooler for garage.

Tier 5: not suitable for home cooling

The Gulf Coast, Florida, the Southeast, the Midwest and Northeast, and coastal areas generally. Summer wet bulbs in the mid to upper 70s F leave no useful margin. Portable coolers sold in these regions mainly act as fans with a humidity penalty.

Why elevation helps

High-elevation towns have three advantages beyond dryness:

• Lower pressure. At the same temperature and RH, the wet bulb is roughly 1 to 2 F lower at 5,000 ft than at sea level.
• Cool nights. Desert nights often drop 30 F or more. A cooler run hard overnight can flush the house with 60 F air and store that cooling in walls and floors.
• Shorter peaks. Afternoon highs above 95 F are less frequent, so a correctly sized cooler rarely runs out of capacity.

Note that thinner air also carries less heat per cubic foot. Above roughly 5,000 ft, sizing guides commonly add some airflow; see how to size a swamp cooler and the cooler size calculator.

Rate your own location in five steps

1. Find your nearest weather station. Use the National Weather Service or NOAA NCEI climate normals, or find your city in our climate index.
2. Get typical July afternoon conditions. Average daily high temperature and the afternoon dew point or RH.
3. Convert to wet bulb. Use the cooling temperature calculator.
4. Predict supply air. Apply the formula with 70% for aspen or 88% for rigid media.
5. Repeat for your most humid month. If the humid-month result stays below about 75 F, a cooler can be your main system. If it rises above about 78 F for weeks, plan for AC or a heat pump as a backup.

Microclimates within a good region

City-level data hides local differences that can shift performance by a few degrees:

• Irrigated neighborhoods and golf courses. Heavy lawn and tree irrigation raises the local dew point slightly, especially in the evening. Older irrigated neighborhoods in Phoenix and Las Vegas can run a little more humid than new desert-landscaped subdivisions.
• Lakes, reservoirs and rivers. Homes right beside large water bodies see somewhat higher humidity on calm days.
• Valley floors and foothills. Cold air drains downhill at night, so valley-floor homes cool off more overnight, which is good for night pre-cooling. Foothill homes are often a few degrees cooler in the afternoon.
• Urban heat islands. Dense pavement keeps nights warmer, reducing the night flush that makes coolers so effective in rural high-desert areas.

None of these change a region's tier, but they explain why two neighbors with identical coolers can report different results. If yours seems weak compared with others nearby, check equipment first; the swamp cooler not cooling guide lists what technicians check before blaming the weather.

Water availability and local rules

The driest climates are often the most water-stressed. A whole-house cooler commonly evaporates 3 to 15 gallons per hour on hot days, plus bleed-off. Some utilities in the Southwest have offered rebates for evaporative coolers because the electricity savings are large, while drought ordinances occasionally limit outdoor water use. Neither usually restricts indoor cooler operation, but check local rules. Estimate your use with the water usage calculator.

When the climate is right but the house is not

Even in Tier 1, a cooler underperforms if the house cannot exhaust air, if ducts are undersized, or if the home has large unshaded west-facing glass. Before blaming the climate, check relief area (venting and relief air), duct sizing and pad condition. If you are comparing systems for a new or renovated home, our swamp cooler or heat pump by region guide adds heating and humidity together.