The researchers found that sleep was “efficient and restful” when the indoor night temperature was between 20 and 25 degrees Celsius (68 to 77 degrees Fahrenheit), and sleep efficiency dropped when the temperature increased from 25 to 30 degrees Celsius (77 to 86 degrees Fahrenheit).
Research shows sleep can be disrupted by temperatures anywhere below 65 degrees Fahrenheit or above 75 degrees Fahrenheit. But for most people, heat interferes with sleep more than cold does. Sleep experts believe the best temperature for great sleep is between 68-72 degrees Fahrenheit.
IMO 80F is the upper limit of comfortable indoor temperatures. It might feel great coming indoors from 110F into 90F, but after you get used to it, the 90 will also feel hot. I don't experience that at 80F or below.
Key takeaways: The highest environmental temperature humans can survive is 104°F to 122°F (40°C to 50°C). But those temperatures aren't safe. A safe temperature range for prolonged outdoor time is 77°F to 88°F (25°C to 31°C).
Consumer Reports has a lot to say on the subject. According to them, the recommendation by the Department Of Energy and Energy Star is to set your thermostat at 78° while home and 85° while away. The recommendation is also for 82° while asleep.
A bedroom that is too warm can interfere with the body's thermoregulation abilities and cause fatigue. View Source . Often, a person who is fatigued will feel physically and mentally tired, but unable to fall asleep. Body temperature also affects sleep quality and the time spent in different sleep stages.
“Typically it is suggested that the optimal sleeping temperature in the bedroom for adults should be between 60 and 67° F,” says Dr. Drerup. This range of temperature is thought to actually help facilitate the stability of REM sleep.
After an influential study in 2010, climate researchers often use a wet bulb temperature of 35 degrees C — roughly equivalent to 95 degrees F at 100% humidity — as an upper limit for human survival and adaptability without cooling.
A core body temperature of 104 degrees Fahrenheit (40 degrees Celsius) or higher is the main sign of heatstroke. Change in mental state or behavior. Confusion, agitation, slurred speech, irritability, delirium, seizures and coma can all result from heatstroke. Change in sweating pattern.
On the other hand, if humidity is up at 100% already (i.e. the air is as saturated as it can possibly be with water - think of a steam room) it's basically impossible for sweat to evaporate so it merely pools on the skin and drips off, taking very little heat with it in the process.
CALIFORNIA OCCUPATIONAL SAFETY AND HEALTH STANDARDS BOARD
Heat Illness Prevention in Indoor Places of Employment. (a) Scope and Application. (1) This section applies to all indoor work areas where the temperature equals or exceeds 82 degrees Fahrenheit when employees are present.
For some people, especially those used to cooler climates, 80 degrees Fahrenheit can feel quite warm. It falls within the range of what we typically call "room temperature" or a little higher. When indoors, it may feel slightly too warm, leading to the use of fans or air conditioning.
Air conditioners make homes more comfortable on hot and humid days. So, it can be frustrating when the AC is not cooling below 75 degrees, even if it has been running for hours. Many factors can cause this issue, including clogged filters, refrigerant leaks and the wrong unit size.
How hot is too hot? “If someone told me that they slept in a temperature between 70 to 75, I'd say that's a range that promotes insomnia,” Avidan says. “That's toasty.” If you're used to keeping your bedroom so warm, “Lower the temperature 2 to 3 degrees at a time,” Ramos says.
In general, 80 degrees is too hot for a house if people are inside. However, if people aren't home during the day or for vacation during the summer, an indoor temperature of 80 degrees can save energy until you return and lower the temperature.
They found that this upper-temperature limit lies between 40℃ (104F) and 50℃ (122F) when the human body stops functioning optimally. Further studies are needed to understand how this happens and offer insights as heatwaves and unusually warm temperatures continue to impact regions across the globe.
Scientists have repeatedly said that Earth would need to average 1.5 degrees of warming over two or three decades to be a technical breach of the threshold. The 1.5 degree goal “has to be (kept) alive because lives are at risk and choices have to be made,” Burgess said.
Some of that heat is well understood: Greenhouse gas emissions from burning fossil fuels reached record levels in 2024, trapping heat in the atmosphere.
For most people, 75 degrees is too hot to sleep, per the National Sleep Foundation. But the new study found that in people 65 and up, sleep efficiency only started to decrease when temperatures were above 77 degrees.
According to Chester Wu, MD, a psychiatrist and sleep expert, one of the best sleep positions is side-sleeping. “This position is ideal as it helps maintain proper spine alignment, reduces snoring and sleep apnea symptoms, and is beneficial for digestion and heart health,” said Wu.