Full Breakdown
Fans May Heat Rather Than Cool in Extreme Heat
7/1/2026, 11:10:26 PM
Fan Effectiveness in the Current Heatwave
During the current European heatwave, fans—often used instead of air-conditioning—can stop cooling and may raise body temperature. The shift from cooling to heating depends on ambient temperature, humidity, and age.
Heatwave Context
Europe is experiencing a “mega heatwave” with reported deaths, prompting many residents to rely on fans for relief. Fan effectiveness under these extreme conditions has become a public-health concern.
Key Researchers and Agencies
George Havenith of Loughborough University in the United Kingdom explains the physics of fan-induced heat transfer. The UK government has issued guidance on fan use, while the World Health Organization (WHO) has set its own temperature threshold for fan effectiveness.
Core Data
- Skin temperature in shade: 35 °C–37 °C (99 °F–99 °F).
- UK government warning: fans may not prevent heat-related illness above 35 °C (95 °F).
- WHO guideline: fan cooling may reverse above 40 °C (104 °F).
- Modeling shows a fan can increase heat gain at 45 °C with 15 % relative humidity.
- Experiments indicate fans still provide cooling up to 38 °C when humidity is 60 %.
- Age reduces sweating, lowering the temperature at which fans become counter-productive.
Official Statements & Responses
The UK government advises that fans become ineffective for preventing heat-related illnesses when ambient temperatures exceed 35 °C. The WHO similarly notes that fan cooling may reverse above 40 °C, emphasizing the need for alternative cooling strategies in extreme heat.
Criticism & Opposition
Studies cited indicate the 35 °C and 40 °C limits are not universal; humidity, clothing, and acclimatization shift the effective threshold. Critics say simple cut-offs ignore these variables, risking public misguidance.
Conflicting Reports & Gaps
The main discrepancy lies between the UK government’s 35 °C limit and the WHO’s 40 °C limit. No consensus exists on a single threshold, and data on how age-related changes in sweating quantitatively shift the fan-effectiveness point remain limited.
Why It Matters
Many households lack air-conditioning, so reliance on fans during the heatwave could increase heat-related morbidity if temperatures exceed the identified thresholds. Wetting clothing or seeking cooler environments becomes essential to reduce dehydration and overheating risk.
Verbatim Quotes
- “So it depends on the humidity in the air,” — George Havenith, Loughborough University
- “That’s why people often look at what kind of climate you have in different countries.” — George Havenith, Loughborough University
- “In this situation, turning on a fan won’t help, because evaporation cannot increase any further.” — George Havenith, Loughborough University
- “For instance, a fan can still cool you at up to 60 per cent humidity and 38°C.” — George Havenith, Loughborough University
- “At that stage, you probably would have to leave your house and find a cooler place,” — George Havenith, Loughborough University
