As a general guideline, evaporative cooling becomes progressively less effective as humidity rises, with diminishing returns above 50% and near-complete ineffectiveness above 60%.
Humidity levels and cooling performance:
| Humidity | Cooling Effect | Comfort Level |
|---|---|---|
| Under 20% | Excellent (20-30°F drop) | Ideal conditions |
| 20-30% | Very good (15-20°F drop) | Still excellent |
| 30-40% | Good (10-15°F drop) | Comfortable |
| 40-50% | Fair (5-10°F drop) | Marginal comfort |
| 50-60% | Poor (3-5°F drop) | Barely noticeable |
| Above 60% | Ineffective | May feel worse |
How to check humidity:
- Most weather apps and websites display current humidity
- Weather.gov provides detailed forecasts including humidity
- Inexpensive hygrometers (humidity meters) cost $10-20
- Smart thermostats often display indoor humidity
Decision guide:
- Below 40% humidity: Run your evaporative cooler normally
- 40-50% humidity: Cooler will work but with reduced effectiveness; consider whether it's worth running
- Above 50% humidity: Switch to fan-only mode or alternative cooling
- Above 60% humidity: Evaporative cooling will add unwanted moisture; don't use the water function
Regional considerations:
Morning humidity is often higher than afternoon humidity in desert climates. You might find your cooler works better in the afternoon. Conversely, during monsoon season, afternoon thunderstorms raise humidity, so mornings may be better for evaporative cooling.
