Help needed. Lightroom very slow, uses >450% CPU and makes iMac fan run significantly

[Ethan Landers]

I used not to have this issue with Lightroom, but now it prevents me from having a good workflow.  Everything is super slow in Lightroom now, and I feel my iMac will explode if I continue using the application due to the extreme CPU usage and the fan running very loudly.  What can I do to resolve this problem?  Just having Lightroom open as the primary window makes my computer go crazy.  It is especially worse when I use, for instance, the healing tool.

Retina 5K 27-inch iMac 2017

Memory 16GB

4.2 GHz Quad-Core Intel Core i7

Ventura 13.4.1

[KR Seals]

The first thing I would check on your iMac is to see if the cooling ducts are clogged with dust or animal hair. You might also run the Mac Activity Monitor to see if other apps are contributing to the workload on the processor.  I'm a MacBook user, but I have several friends on iMacs of that vintage and they don't have that issue with the latest version of Lightroom Classic.

[dj_paige]

Fans run because there is heat building up inside the case. Heat must be dissipated, so you need to check the entire cooling system to make sure it is working properly, including fans and vents. Vaccuum out all exterior vents. Consider getting a laptop cooling device.

[KR Seals]

It's an iMac, not a laptop.

[dj_paige]

It's an iMac, not a laptop.

By @KR Seals

Oops, the laptop cooling device is not going to work. Everything else I said is still good advice. Check the cooling system. Vaccuum out the case vents.

[Conrad_C]

If the CPU is often at 450%, then it isn’t purely a heat problem, or the heat is because the CPU is very busy. In Lightroom Classic there are various background operations that can do chores when nothing is happening, do you know if it makes any difference if these are disabled? Some include:

• Replace Embedded Previews with Standard Previews During Idle Time (in Preferences / General) 
• Generate Previews in Parallel (in Preferences / Performance) 
• Address Lookup and Face Detection (Identity Plate) 

These background operations are usually no problem on newer Apple Silicon Macs with lots of efficient (cool running) CPU cores to spare, but they are more likely to strain an 6-year-old iMac that has only four Intel CPU cores.