Waves of extreme heat have already passed across the United States, Europe, and other parts of the world so far this summer. While people are at the greatest risk from high temperatures, your Mac may be even more fragile. (People can be water cooled and no current Mac offers that option—though some have tried.) An iPhone or iPad will warn you when it detects it’s too hot before shutting down, while a Mac may simply suddenly power off. If it doesn’t power down, you may be running it to close to its maximum capability and putting a lot of additional wear in the process on components that might fail later during other seasons.
Knowing the temperature is one thing. The other is how hot should your internal components run? Apple says you should only use a Mac when the ambient temperature—the temperature around you—is in the range of 50°F to 95°F (10° to 35°C) and 95 percent or lower humidity.
Internal components produce far more heat than the ambient temperature, with around 100°F or 40°C often the minimum at which they operate in normal indoor circumstances. CPUs, GPUs, ports, and other elements shouldn’t exceed about 192°F (89°C) for extended periods. At 212°F (100°C), the boiling temperature for water at sea level, you should either figure out what energy hogs are making your computer work that hard or shut the system down for a while. (Hint: It’s almost always a browser.) You can use the Activity Monitor app in Applications > Utilities to look at Energy Impact in the Energy column for more particulars.
Read more at Macworld.com