Quick answer: an evaporative (“swamp”) cooler cools air by evaporating water, so it works best when the air is dry. In Arizona that means late spring and June, before the monsoon. From July through September, higher humidity cuts how much it can cool. A portable cooler is a good fit for a garage, patio or workshop, or as a supplement in dry months, but not as the only thing protecting someone vulnerable in a heat wave.
At a glance
- Phoenix average dew point, June
- About 38°F (dry) [1]
- Phoenix average dew point, August
- About 58°F (sticky) [1]
- Tucson average dew point, June vs. August
- About 36°F vs. about 59°F [1]
- NWS comfort scale
- 55°F dew point or lower feels dry; 65°F or higher feels oppressive [2]
- Heat-related deaths in Arizona, 2024
- 977, including 336 where the injury happened at home [3]
How humidity changes through an Arizona summer
The National Weather Service uses dew point, not relative humidity, to describe how much moisture is in the air: at 55°F or lower it feels dry, from 55°F to 65°F it gets sticky, and at 65°F or higher it becomes oppressive [2]. Evaporative coolers do the most when that number is low.
NOAA’s 1991-2020 hourly climate normals show how sharply that changes in Arizona’s desert cities [1]:
| Month | Phoenix avg. dew point | Tucson avg. dew point | Phoenix avg. temperature |
|---|---|---|---|
| May | 34°F | 29°F | 83°F |
| June | 38°F | 36°F | 92°F |
| July | 54°F | 55°F | 96°F |
| August | 58°F | 59°F | 94°F |
| September | 51°F | 52°F | 89°F |
Averages of NOAA’s hourly normals for each month, rounded; daily highs are much hotter. [1]
June is the sweet spot: the hottest dry month. Once monsoon moisture moves in, average dew points climb about 20 degrees between June and August, and the National Weather Service warns that heat-related deaths often rise because “typical summertime heat is combined with increased monsoon humidity” [4]. One cooler maker, Portacool, puts numbers on it: it says its APEX coolers drop temperatures 10 to 13°F in hot, humid spaces and up to 30°F in arid ones [5].
How we chose
- Sized by the maker’s airflow and coverage. We list the maker’s CFM (cubic feet per minute) and stated cooling area.
- A real water supply. Bigger tanks or a hose connection mean fewer refills on 110°F days.
- Specs from the maker’s own page. Where the maker doesn’t publish a cooling area or a safety listing, we say so.
- No recall. We searched the Consumer Product Safety Commission recall database for each brand on November 2, 2026 [9].
Our picks
Best for: A single room, home office or small patio
Hessaire MC18M 1,300 CFM Mobile Evaporative Cooler
It's a small, light unit for spaces up to 500 square feet, and it draws only 85 watts.
- 1,300 CFM; up to 500 sq ft, per Hessaire [6]
- 4.8-gallon tank [6]
- 85 W, 0.7 A [6]
- 28 x 20 x 10 in.; 16 lb [6]
Safety check: Hessaire's page doesn't list a safety certification [6]. No CPSC recall found for Hessaire (checked 2026-11-02) [9].
Watch out: A 4.8-gallon tank needs frequent refills in dry heat, and it won't do much in a closed room once monsoon humidity arrives.
See it on Amazon → We chose it from specs and safety records; we haven't tested it ourselves.
Best for: Garages and larger rooms
Hessaire MC37M 3,100 CFM Mobile Evaporative Cooler
It moves more than twice the air of the MC18M, has variable speed control, and can hook up to a continuous water supply.
- 3,100 CFM; variable speed [7]
- 10.3-gallon tank; continuous water connection [7]
- 250 W, 2.4 A [7]
- 24 x 16 x 38 in.; 40 lb [7]
Safety check: Hessaire's page doesn't list a safety certification [7]. No CPSC recall found for Hessaire (checked 2026-11-02) [9].
Watch out: Hessaire doesn't state a cooling area for this model, so size it by airflow and check with the maker.
See it on Amazon → We chose it from specs and safety records; we haven't tested it ourselves.
Best for: Shops, garages and covered patios up to about 1,350 sq ft
Portacool APEX 700 Portable Evaporative Cooler (PACA07001A1)
It has a 22-gallon tank and a 3/4-inch hose connection for long runs, and the maker rates it for up to 1,350 square feet.
- 1,600 CFM; up to 1,350 sq ft, per Portacool [8]
- 22-gallon tank; 3/4 in. hose connection [8]
- Standard 120 V [8]
- 52 x 27 x 24 in.; 88 lb [8]
- Lifetime warranty on the molded housing [8]
Safety check: Portacool's page doesn't list a safety certification [8]. No CPSC recall found for Portacool (checked 2026-11-02) [9].
Watch out: At 88 pounds empty, it's heavy, and Portacool doesn't list its wattage on the product page.
See it on Amazon → We chose it from specs and safety records; we haven't tested it ourselves.
Best for: Cooling part of a house in the dry season
Hessaire W3800 Window Evaporative Cooler
It mounts in a window, pulls in outside air through wet pads, and Hessaire rates it for 1,100 square feet.
- 3,800 CFM; up to 1,100 sq ft, per Hessaire [10]
- 1/3 HP motor; 115 V, 5.5 A [10]
- GFCI-protected receptacle required [10]
Safety check: Requires a GFCI-protected outlet, per Hessaire [10]. No CPSC recall found for Hessaire (checked 2026-11-02) [9].
Watch out: It needs a water line and a window it can be mounted in, and it's the least useful during monsoon humidity. Hessaire's page has few other details, so read the manual before buying.
See it on Amazon → We chose it from specs and safety records; we haven't tested it ourselves.
Buying guide
- Match it to the season and the space. Evaporative coolers do the most in dry heat and in open or well-ventilated spaces like garages and patios.
- Size by airflow. Compare CFM and the maker’s stated coverage, not the box’s “up to” temperature drop.
- Plan the water. Bigger tanks or a hose hookup make a real difference in Arizona summers.
- Watch the dew point. When it’s 55°F or above, expect less cooling [2].
- Have a backup. A swamp cooler isn’t a substitute for air conditioning or a cooling center during an Extreme Heat Warning.
Sources
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991-2020, hourly (Phoenix Sky Harbor USW00023183, Tucson International USW00023160)
- National Weather Service La Crosse: Why Dew Point vs. Humidity
- Arizona Department of Health Services: Heat-Caused & Heat-Related Deaths in Arizona, 2013-2024
- National Weather Service Phoenix: Monsoon Safety
- Portacool: home page (APEX Series performance statement)
- Hessaire: 1300 CFM Mobile Cooler
- Hessaire: 3100 CFM Mobile Cooler
- Portacool: APEX 700 Portable Evaporative Cooler
- U.S. Consumer Product Safety Commission: Recalls (searched November 2, 2026)
- Hessaire: Window Coolers
Common questions
When do swamp coolers work best in Arizona?
When the air is dry. In NOAA's 1991-2020 hourly normals, Phoenix's average dew point is about 38°F in June but about 54°F in July and 58°F in August, after monsoon moisture arrives. Tucson follows the same pattern. Evaporative cooling does the most in the dry months and less during the monsoon.
How much cooler can an evaporative cooler make the air?
It depends on humidity. Portacool, one maker, says its APEX coolers lower temperatures by 10 to 13°F in hot, humid spaces and up to 30°F in arid ones.
Can I rely on a portable swamp cooler during an extreme heat warning?
Be careful. Arizona's Department of Health Services counted 336 heat-related deaths in 2024 where the injury happened at home. The National Weather Service warns that monsoon humidity combined with summer heat raises the danger. If your home gets too hot, go to an air-conditioned place or a cooling center.