Indoor Heat Myths and Facts

This is a fact! Fans can help cool the body up to certain temperatures, but do not actually cool the air in a room.

Fans work by moving the air around in a room, but are only circulating the existing air within a room at whatever temperature it is, and not cooling the air itself. If air temperature is below skin temperature (approx. 34 °C, up to 36 °C when it is very hot), then the breeze created by fans will improve heat loss by convection and by evaporation of sweat. These two things combined will minimize any increase in core temperature that would occur without a fan. However, it is important to stay hydrated for this to be effective.

Tip: If using Air Conditioning, set the thermostat to 27˚C / 81˚F and turn on an electric fan – this will make the room feel 4˚C cooler.

Notes: 

• In very hot and dry situations (above 40˚C / 104 ˚F), fan use can be extremely dangerous and even increase body temperature.
• It’s a good idea to have at least one window open when turning on your fan, but only if the outdoor air is cooler than the indoor air. 

Sources:

• Malik et al. (2022) The potential for indoor fans to change air conditioning use while maintaining human thermal comfort during hot weather: an analysis of energy demand and associated greenhouse gas emissions
• Kent et al. (2023) Energy savings and thermal comfort in a zero energy office building with fans in Singapore

This is a fact! The type of clothing you wear can make a big difference to your body temperature.

Generally, light-coloured and loose clothing can improve thermal comfort. Synthetic fabrics such as acrylic and nylon trap sweat and heat from your body, increasing your body temperature. Natural fabrics (cotton, silk, and linen) do the opposite – they allow heat to escape from the body more easily.

This is a myth! All people are at risk from extreme indoor heat.

We should all follow public health guidance and take precautions to protect our health and the health of those we live with. However, some groups are at greater risk than others. These groups include people over 65 years of age and those with chronic medical conditions, infants and children, pregnant women, and the poor or others living or working in spaces with inadequate cooling - including indoor workers who are exposed to heat generated from occupational processes or equipment and metabolic heat production.

This is a myth! Although people are often advised to stay inside during an extreme heat event, indoor temperatures may be higher than outdoor temperatures.

For example, a shaded area in a park may be cooler than an apartment near the top of a building that does not have mechanical cooling. Always follow local public health advice and seek out safe cool spaces. Avoid direct exposure to the sun during peak hours, seeking shade or staying indoors if it’s cooler instead.

This is a myth! Well-maintained and operated air conditioning units are unlikely to make people sick, and they can be critical life saving devices during extreme heat events.

A space should be always ventilated, and both natural and mechanical ventilation are possible.


Note: Mechanical cooling does contribute to global emissions, through both the energy used to power air conditioners and the refrigerants used within the devices. Efforts to decarbonize our energy system and to advance more sustainable cooling technologies are critical. In the meantime, we must work to find a balance between reducing wasteful air conditioning use, while also ensuring those who need it (such as for medical reasons) have equitable access. 

Tip: If using Air Conditioning, set the thermostat to 27˚C / 81˚F and turn on an electric fan – this will make the room feel 4˚C cooler.

Sources:

• Malik et al. (2022) The potential for indoor fans to change air conditioning use while maintaining human thermal comfort during hot weather: an analysis of energy demand and associated greenhouse gas emissions
• Kent et al. (2023) Energy savings and thermal comfort in a zero energy office building with fans in Singapore

This is a fact! Our choices of foods and beverages affect our body’s ability to cool down.

Alcohol and caffeine are not recommended on hot days. Choosing light foods with high water contents, keeping water with you, and making a habit of drinking water are some easy ways to help maintain healthy hydration.

This is a fact! Heat events become more dangerous the longer they last.

It is important that during long periods of hot weather, you consistently take measures to protect your health from extreme temperatures, such as by staying in a cool space whenever possible. This is particularly important when temperatures do not drop throughout the day or overnight.

References:
- Meade, R. D., Akerman, A. P., McCormick, J. J., King, K. E., Sigal, R. J., & Kenny, G. P. (2023). Efficacy of Cooling Centers for Mitigating Physiological Strain in Older Adults during Daylong Heat Exposure: A Laboratory-Based Heat Wave Simulation. Environmental Health Perspectives, 131(6). https://doi.org/10.1289/EHP11651
- McGarr, G. W., Meade, R. D., & Kenny, G. P. (2023). Indoor overheating influences self-reported symptoms and mood-state in older adults during a simulated heatwave: Effects of mid-day cooling centre use. Physiology & Behavior, 271, 114335. https://doi.org/10.1016/j.physbeh.2023.114335

This is a fact! Feeling thirsty is your body’s way of letting you know you need water. However, as we age, our thirst response becomes weaker and our kidney function declines.

This increases the risk of older adults becoming dehydrated and suffering from heat-related impacts. 

Note: Also young children are at higher risk from dehydration as they cannot communicate their need for water. 

This is a myth! While our bodies can develop some tolerance and adapt to heat, nobody is immune to the risks associated with extreme heat events, especially if you are exposed to heat for a long time.

In historically hot countries (e.g. India, Bangladesh), thousands of people have lost their lives during extreme heat events.

Note: As the summer progresses, people can become more adapted to the heat. However, this may not apply to everyone (especially older adults or people taking medication), and your acclimatization might not be enough to cope with very hot conditions, especially over multi-day periods.

This is a fact! When hot air touches a wet cloth, it grabs onto warm water molecules, cooling the damp fabric, and, consequently, the air.

Another way to cool down body temperature is by applying ice packs or wet cloth to areas like the neck, under the arm, and in the groin, where major blood vessels are near the skin surface. Staying cool so that you can get complete sleep is important for both physical and psychological health.

Tip: Never cover an infant stroller / pram with dry fabric – this makes it hotter inside the carriage. Instead, use a wet, thin cloth and re-wet as necessary to lower the temperature. Combine with a portable fan for even greater cooling.