Home / The guide / Heating and cooling
Heating and cooling · Cool the house, passive first · thermal-14Use evaporative cooling only in dry climates
Evaporative coolers blow outdoor air through wet pads and can drop its temperature by about 8 to 22 C (15 to 40 F) using a fraction of an air conditioner's energy. They add moisture, so they fail in humid climates.
How
- Confirm your climate is suitable from thermal-3. At 100% humidity there is no cooling at all.
- Choose direct, indirect or two-stage units. Indirect and two-stage designs add less or no moisture indoors.
- Size by airflow; DOE says manufacturers suggest 20 to 40 air changes per hour depending on climate.
- Provide relief openings: PNNL calls for about 2 sq ft (0.19 m2) of unrestricted relief area per 1,000 cfm, larger if screened.
- Budget the water: PNNL examples for a 1,500 sq ft home in the US Southwest without a bleed-off valve range from 2,980 to 12,457 US gallons (about 11,000 to 47,000 litres) a year. PNNL says a bleed-off valve adds 10 to 50%, so add up to half again if you fit one. Pass this to the water module.
- In humid climates, use an inverter air conditioner or heat pump instead, which also dehumidifies.
Safety: Keep pads, pans and reservoirs clean and drained when not in use to limit bacterial growth.
Do these first
Sources
- Evaporative Coolers. U.S. Department of Energy, Energy Saver, accessed 2026-11
- Evaporative Cooling Systems. Pacific Northwest National Laboratory, Building America Solution Center, accessed 2026-11