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I have a question concerning fan noise and overheating in 2019 27“ iMacs. I am about to choose one, either the base model or the 9th gen core i5 for more processor power.

From your experience with previous models, does loud fan noise due to overheating also occur for the base models, or is this a problem of the higher end processor choices?

It seems that the thermal design power of the base model currently is 65W, but both for the 9th gen i5 and the i9 it is 95W. Would this mean that the high end i5 is as bad as the i9 in terms of expected fan noise, i.e. similar problems as for earlier i7s should be expected? For the graphics cards, it is currently 120W vs 150W in favor of the base model.

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From your experience with previous models, does loud fan noise due to overheating also occur for the base models, or is this a problem of the higher end processor choices?

Unfortunately, in the Apple community, this is a common miscorrelation. So, let's first set the record straight...

Fan Activity ≠ Overheating

Just as the radiator fans in your car periodically come on to move additional air across the radiator, the fans in your computer (PCs and Macs) spin up to move additional air across the fins on the heat sink in an effort to dissipate heat.

Hearing fan activity is a perfectly normal and expected behavior regardless of the processor, memory, or general specifications of the machine.

Fan Noise

There are only two fan noises that you should be concerned with:

  • Squealing and/or grinding indicating a failed bearing
  • No fan spin at all indicating a full failure

Overheating

Like your car, you will know exactly when your computer overheats. It will slow down and eventually shut off. Granted, there's much more fan fare with a car, usually with steam and coolant gushing everywhere though with the computer, lost work can make you feel pretty steamed and some choice expletives are also probably going to come gushing out at well.

However, unlike your car, this is by design. Your processor will thermally throttle it's speed limiting what it can do and if all else fails, it will power off in a bid to save itself.

It's not just the CPU

The fan spins up because the overall temperature within the chassis is high enough to warrant it. This can be from the CPU, the GPU, the drives, the logic board and in the case of AiOs (iMac), the display and the power supply. Even the ambient external temperature is a factor. All of that contributes to the internal thermal conditions which may necessitate the need to spin up the fan.

TDP or Thermal Design Power

TDP is the maximum amount of heat that your processor will generate on average use. A higher number means it will allow more and higher processes before it gets into the "red zone". In other words, a processor with a higher TDP will do more before the fans spin up or throttles back to cool off. In your case, comparing the 9th generation i5s with previous generations, you get a higher TDP because the chips are more efficient, not that they generate more heat.

Fan Control Software

Unless you intend to manually increase the fan speed in an effort to keep things extra cool, this is the worst thing you can do. Slowing the fan in a bid to make it more audibly aesthetically pleasing will only result in one thing - putting a cap on the processing power of the machine you paid money for. This is like buying a high performance car and immediately installing a restrictor plate.

Bottom Line

Buy the iMac that meets your needs (CPU, GPU, memory, storage). Fan spin shouldn't be part of that equation.

  • I will often force the fans on my MBP to run at max (6000 or so) to get the quickest possible compiles. I barely notice it. The iMac Pro is even quieter, even with the fans set to max revs. Unless you have your iMac in a strange acoustic situation or have the ears of an 8-year old, it's unlikely they'll bother you. I've worked in data centers with server fans going full bore. THAT's fan noise. I doubt any iMac will sound like a vacuum cleaner. Let me ask the original poster...have you heard the fans on an iMac, in a normal situation, and found it annoying? – Wilfred Smith Mar 30 at 1:00
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Keep in mind that the TDP is "typical." If the processor is idle, it may use considerably less power. If you're hitting all the cores/threads hard AND the GPU, that's where you'll hear the fans spin up and holler at you.

For the same processor generation and process (e.g. 10nm, 15nm, 17nm, whatever), the same workload will generate a very similar heat load regardless of the number of cores/processor speed. However, if you have more cores/threads/higher processor speed, the system may try to do more work in a shorter period of time. That can cause the fans to spin faster, but for a shorter period of time.

My suggestion is to get the base model, then download a fan control utility to set a reasonable limit on the fan speed. When the processor gets hot, it'll just throttle down and run slower.

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