Keep fans on or off?

[BDev]

Simple question. I have some extra coolers in my case, and they are quite silent so putting them on low or off makes absolutely no "sound difference" but i just wanted to know if i should or not keep them on at all while my PC is idle / passive mode or while browsing the internet, because for me it makes no sense as my GPU is often at 27°C (i have no idea What's my CPU temp but it's cooler is like ALWAYS at high rpms so i don't really care). So, should i let them on or off?

[W-L]

2 minutes ago, BDev said:

Simple question. I have some extra coolers in my case, and they are quite silent so putting them on low or off makes absolutely no "sound difference" but i just wanted to know if i should or not keep them on at all while my PC is idle / passive mode or while browsing the internet, because for me it makes no sense as my GPU is often at 27°C (i have no idea What's my CPU temp but it's cooler is like ALWAYS at high rpms so i don't really care). So, should i let them on or off?

If you want your system as dead silent as possible having them stop isn't a bad idea, they can turn on a ramp up if needed when the system get warm enough. If your CPU cooler is at high RPM check your temps or fan curves to see if it's one of the two reasons. 

[haifisch]

Bearings tend to be louder over time. So if you keep the fans off while not needed, you preserve their quietness and they will have a longer lifespan. I don't really know by how much in real life though.

For your cpu fan, check the temps, and if they are fine, chech the bios settings for fan curves. If you see high temps, reapply thermal paste. Use top quality paste, it can make your cpu run multiple degrees celsius cooler than with lower quality paste. Also, is the cpu fan pwm?

[NotTristan]

I mean it all depends on priorities. If your priority is silence, then don't have any fans, simple as that. Although you might sacrifice on temperatures. you can go into your BIOS to lower the rpm of your CPU fan, keep in mind your processor can get hotter than you might think. seeing at 70C shouldn't be a problem unless you are using it for a very long time at 70C. So if you use somethin glike AIDA64 and it hits 70, you should be fine as you will probably never get to that high of a load in the real world. And both posters before me are correct, the more you run the fans the less they will last (even if it is by a small amount) and you can set them to turn off untill your system gets to a specific temp and they will turn on.