Some iPhone 15 users are complaining their smartphones are getting too hot, but not everyone feels the burn, and in nearly every case, the temperatures are still within spec.
Just like any other major piece of hardware that is regularly updated, the release of a new iPhone model invites scrutiny from industry observers, critics, and early adopters. While the complaints and fears cover a number of areas, one that has resurfaced for the iPhone 15 is claims of the device overheating.
It's been less than a week after release, and there have been reports of the latest model getting a bit toasty when under certain scenarios, but especially in the time after wireless charging has stopped.
In a number of instances, people have complained that their iPhone has gotten hot, or more specifically, a bit too warm to use comfortably. Complaints range from seeing temperatures rise above 40C, to others who find slightly lower temperatures to be a little worrying.
Others are also taking to social media to confirm their iPhone isn't affected by overheating at all.
It is unclear why some users experience hot iPhones while others don't have trouble at all. One of our editors had some issues over the weekend, but they've cleared since. Another never had any problems at all.
While many could take the heating to be a problem, it may not really be an issue. An iPhone heating to 44C isn't entirely abnormal behavior, despite the personal distress it may cause.
Excluding problems like the rare battery rupture, an iPhone can heat up in a variety of ways.
The most obvious is environmental factors, namely where you're placing the iPhone, regardless of your actual use of it. Leaving it out in the sun on a very hot day can certainly heat up the iPhone, even without it being turned on.
An iPhone can heat up in a few ways, and it basically boils down to transfers of energy or the usage of energy.
The first, transfers of energy, refers to when you recharge an iPhone's battery. Whether by wireless charging over Qi or MagSafe, or using a physical cable, the transfer of power isn't a perfect process, and heat can dissipate.
Heat generation also occurs with the battery itself, since recharging a battery is a chemical reaction that produces heat as a byproduct. While batteries don't tend to get warm through discharge, they do get a lot warmer when you're recharging the device, simply because of that exothermic chemical process.
Complaints of hot iPhones after charging are common, simply because charging devices tend to get things warm. It's an almost unavoidable issue.
The other way an iPhone can get warm or hot is through usage. Running games and intensive applications that consume more resources and power than typical can warm up components like the CPU and GPU over time.
In Apple's hardware, the CPU and GPU are on the same system-on-chip (SoC), which makes things a bit tougher to deal with.
It is plausible for more pedestrian tasks to warm an iPhone up, such as phone calls, but only to a very negligible degree that most people won't consciously notice. A gaming session that hammers the CPU and GPU however, could quickly lead users to notice their iPhone is getting toasty.
It also doesn't help that iPhones are also dealing with a background task that should complete within a week. The update to iOS 17, as well as the transfer of files from one iPhone to another as part of an update process, triggers the multi-day indexing of files by Spotlight.
This reindexing consumes resources, including battery and processing performance, until it concludes. This can take up to a week.
What probably isn't the problem is Apple's new A17 Pro chip, included in the iPhone 15 Pro and Pro Max. According to analyst Ming-Chi Kuo on Tuesday, a supply chain survey indicates that the reported overheating issues are unrelated to the chip's use of TSMC's 3-nanometer process.
Instead, the primary cause is reckoned to be "compromises made in the thermal system design to achieve a lighter weight," including a reduced heat dissipation area and the use of a titanium frame.
Kuo believes Apple will address the issue through software updates, but it may be limited "unless Apple lowers processor performance."
There have also been accusations that it's a software issue. An anecdote from YouTuber MKBHD mentioned how a five-minute scroll on Instagram during a flight resulted in a brief period of overheating and a drop in battery level, for what would normally be a fairly pedestrian use of the iPhone.
Testing by iPhonedo to see if it was software seemed to bring up similar results, but on an iPhone 14 Pro and iPhone 14 Pro Max that had been updated to iOS 17 and was running iOS. A ten-minute session of minimal Instagram usage with the app open resulted in heat and a 10% drop in battery life.
While iPhonedo found that the iPhone 15 Pro Max had the same problem with Instagram and iOS 17, the testing at least pointed out in that some of the overheating claims could simply be put down to an app issue.
Heat generation is only part of the problem, as the other is to get rid of it. Unfortunately, that's quite a difficult thing for the iPhone to pull off.
A computer like a Mac or a gaming PC will often have a lot of thermal management systems in place that can wick heat away from sensitive components and dissipate it. They can also afford to do so without necessarily impacting the user's usage of the hardware, since they are efficient or are constructed to deal with even higher heat levels without breaking a sweat.
For example, a gaming PC may use large heatsinks and fans to pull heat away from the CPU and to transfer the heat into the air, or use a water cooling loop for the same effect. The MacBook Air can do the same thing by channeling the heat into the aluminum casing, which is a large piece of metal that can spread the warmth and more effectively cool down than an unassisted SoC.
Given the small size and the lack of ability to include active cooling such as fans, the iPhone simply doesn't have the systems available to cool down quickly. Nor can it do so in a manner that can allow the user to continue using the iPhone without seeing some level of performance loss.
The heat from the chips has to go somewhere, and for the iPhone, there's no choice other than for it to transfer to the body of the iPhone itself.
Some Android device producers, like Samsung in the Galaxy S23, are using vapor chamber cooling techniques to move heat around a device. Using tubes containing liquid, hot elements can evaporate the substance, which moves to other cooler parts of the chamber to condense, shifting heat in the process.
Doing so can be helpful for devices that are intended to be used intensively for extended periods of time, but typically at a cost in consuming space within the body of the device. For tightly-packed devices where space is at a premium, smartphone producers can't really use such techniques without some level of engineering compromise.
That said, Apple did reportedly test using vapor chamber thermal systems in iPhones back in 2021, though it allegedly decided against the idea due to poor reliability test results.
The lack of active iPhone heat dissipation is something that a few accessory vendors have picked up on.
It did so by combining a perforated case structure with a Thermaphene performance layer that collected and transferred heat from hot areas to cool ones.
What Apple says about iPhone heat
The page specifies that use in ambient temperatures between 0C and 35C (32F and 95F) is expected, but too high or too low temperatures can impact the hardware, to the level that the iPhone can attempt to regulate its temperature.
When temperatures hit -20C (-4F) or 45C (113F), Apple advises to store the device somewhere safe. These are external temperatures, obviously, and internal temperatures are likely to be higher. Intel, for instance, has set CPU temperature limits at 100C.
Based on this, many complaints that cite temperatures below 45C are more about users worrying about a warm iPhone, rather than one that Apple actually believes is hot enough to be an issue.
Anyone complaining about a 35C or lower temperature for their iPhone are doing so in a range that Apple deems to be perfectly acceptable.
If the iPhone's interior temperature exceeds a normal operating range, the iPhone's protections will kick in. This can include slowing or stopping charging until heat reduces, a dimming of the display, and a throttling of chip performance.
In some instances, you may notice a weaker phone signal or that the flash is disabled, again to temporarily reduce heat generation.
Depending on the heat level, users may also see alerts explaining that the iPhone needs to cool down, before the display is turned off, or that charging is "on hold" until a normal temperature is reached.
An iOS 17 fix
On September 30, Apple issued comments on the overheating talk, with it explaining it was aware of the reports, and that it was working to fix the issues.
Apple's comments initially explained that the first few days after restoring an iPhone or setting up a new one can have some "increased background activity," which can lead to an iPhone running "warmer than expected."
Apple also confirmed there was a bug in iOS 17 that impacts some users, and that it "will be addressed in a software update."
There was also a confirmation that third-party apps were also problematic, with some recent updates "causing them to overload the system." Apple claimed to be "working with these app developers on fixes that are in the process of rolling out."
While the software fix and working with third parties to adjust their apps could help some users, it's entirely plausible that some overheating could still occur in the iPhone 15, especially if Kuo's claims over thermal design compromises are found to be true.
Everything is (probably) okay
The complaints about high temperatures are to be expected for iPhones, or for any other smartphones or highly-used devices with similar thermal constraints. It's been a complaint that has circulated for literal decades in various forms for different hardware, and it's something that can't be instantly mitigated in such cases.
While an iPhone with a temperature approaching 40C may be alarming for the end user, Apple's engineering has made the iPhone capable of working while in such a state. Sadly, Apple's teams cannot re-engineer human comfort levels.
For the meantime, iPhone owners should continue to use common sense when dealing with warm or hot devices — if a hot thing is too hot to handle, stop handling it.
And, if the issue persists for you beyond the first week of use, get it documented with Apple. They won't do anything without data from the service and support chain.