The EPA's Excessive Heat Events Guidebook warns against relying on fans when the heat index is above 99 degrees Fahrenheit. The World Health Organization's Regional Office for Europe similarly cautions that “at temperatures above 35 [degrees Celsius (95 degrees F)] fans may not prevent heat related illness.”
"The way a fan keeps you cool is that it either blows cold air across your skin so you lose heat via a process called convection and it helps sweat evaporate faster," Dr Jay said. "When the air goes above 35 degrees Celsius, you're no longer losing heat via convection.
As the air temperature rises, air flow is increasingly ineffective in cooling the body until finally, at temperatures above about 100° F (the exact number varies with the humidity) increasing air movement actually increases heat stress.
The current guidelines by public health officials vary, with some recommending upper limits for fan use that range from 90 degrees at 35 percent humidity to others advising no fan use above 96 to 99 degrees with no humidity level stated, according to background information in the study.
A wet-bulb temperature of 35 °C, or around 95 °F, is pretty much the absolute limit of human tolerance, says Zach Schlader, a physiologist at Indiana University Bloomington. Above that, your body won't be able to lose heat to the environment efficiently enough to maintain its core temperature.
But any temperatures above 86 degrees Fahrenheit (30 Celsius) can be dangerous and deadly.
Sleeping too hot
“Heat is a huge disruptor for REM sleep,” Dr. Drerup says. With the heat of the room, your body temperature will also rise, thus undoing the sleep initiation process entirely. If your bedroom temperature is above 70° F, it's too hot.
"Fans at any temperature up to 104°F, where there is some kind of humidity, are beneficial," says Jay. "But as the temperature goes higher, if it's dry then fans are progressively less useful... Researchers say that when temperatures rise above 95 degrees, a fan might make you even hotter, and maybe even sick.
A ceiling fan does not actually lower the overall temperature in a room, but it can definitely make a space feel cooler. Ceiling fans primarily work through something called a wind chill effect. Essentially, the moving air across your skin helps to evaporate sweat at a faster rate.
The fan won't actually change the temperature of the room, it will just make it feel warmer. Be sure to turn it off when you aren't in the room to save energy. You only need your fan on the lowest setting to get the benefit. Any higher and you might actually feel colder.
If air temperature rises, the air density decreases, and that air takes up more space. Because air compressors can only intake a fixed volume of air, a decreased density results in less air within the system.
Your AC has limits, no matter its age, how well it was installed, its manufacturer, etc. As a rule of thumb, when it's 95 out, your AC can cool your house to approximately 70-80. Your air conditioner will be able to cool to about 15-25 degrees from the outside temperature.
According to Sleep Advisor, sleeping with a fan on might not always be a great idea for health-related reasons, as although having a fan on will circulate air to make your room cooler and fresher, it can also circulate pollen and dust.
The fan is a cost-effective way to keep you cool during the hot and humid summer nights. But sleeping with the fan on may trigger congestion, dryness, sore muscles, or allergic reactions in some people. If you have allergies but sleep hot, try using air filters and humidifiers to reduce symptoms of allergies.
Some people fear that a ceiling fan will overheat and catch fire if left running overnight; however, these fears are unreasonable. Ceiling fans are designed and manufactured to run for hours on end, and if you invest your money in a reputable brand, you shouldn't have any fears.
Your Air Vents are Closed or Obstructed
If you have closed your air vents, or your vents are obstructed by furniture or upholstery, proper airflow is disrupted. This can most certainly cause some rooms in your home to be hotter than others while placing extra strain on your HVAC system.
Method 1: Face cloth or small towel
Wring the cloth out so that it's damp, not dripping wet. Lay the cloth over the fan. As it blows the air out, it'll circulate through the cloth and the air will feel cooler.
However, fan placement matters. Place your fan so that it faces the opposite wall from where most of the activity takes place in your space. This approach will drive the air to the surface, where it will bounce off, mingling with the rest of the air and cooling the space.
Basically, we might actually be heading towards a lower ideal body temperature, but that's perfectly fine… we'll get used to it. For now, here's your takeaway—the ideal body temperature is not 37 degrees Celsius (98.6 degrees Fahrenheit), but actually closer to 36.4 degrees Celsius (97.5 degrees Fahrenheit)!
A ceiling fan doesn't actually cool a room's temperature, but it creates a wind chill effect by pushing air over your body.
The moving air produced by a ceiling fan makes you feel cooler than you really are, and can make a room feel up to 8 degrees cooler. This is especially helpful at night when temperatures drop but there's still humidity in the air.
23 degrees would be too hot to sleep. In fact, it might make it uncomfortable to fall asleep. The ideal temperature should be around 15-19 C. On the other hand, temperatures below 10 C are also not considered optimal for sleeping.
This may vary by a few degrees from person to person, but most doctors recommend keeping the thermostat set between 60 to 68 degrees Fahrenheit (15.6 to 20 degrees Celsius) for the most comfortable sleep. Sleep Guidebook.
Dr Carmel Harrington, author and sleep specialist at Sleep For Health, says: Our ideal body temperature for sleep is 18 to 19 degrees Celsius. Every degree above that makes it harder to sleep – and anything over 25 degrees can make for a very uncomfortable night.