We see it again and again, both with AIOs and massive custom cooling loops – fans that are running needlessly high. Buying something expensive is not always enough, it also must be set up properly, and this topic is a great example.
First, let's look at an example. Chad just won the lottery and has decided to finally build his dream PC, so he buys the biggest case he can find, and puts custom water cooling on all his components.
Chad doesn't understand the concept of a value proposition so he also has the most expensive CPU he could find. It uses a lot of power, and gets very warm, but this is surely not an issue since his massive custom cooling loop should be able to keep that cold. Chad has also disabled all power limits on his motherboard as he wants to be able to get the most out of his CPU.
Chad has made one big mistake though – he does not have any clue about what his water temperature is, and has just put his fans on his motherboard, or the controller they came with that just defaults to CPU temperatures (it is worth noting that if Chad had purchased a pump/res combo from our Hydro X line-up he would not have this problem as they all come with a built in temperature sensor).
Chad is now upset, since his very expensive computer still makes a lot of noise when he loads up his 342 chrome tabs, or his favorite game. Surely something must be wrong?
Not really – because no matter how big a cooling system he has, his CPU will jump up and down in temperatures when put under load – even short loads. Downloading a steam game, or opening an application on your PC can be pretty taxing on your CPU, but only for a short amount of time.
Chad wants to download a game on steam. Since he has a very fast internet connection, the game will download fast, and put a lot of load on his CPU as it need to be saved to his blazingly fast SSD as well. Chad has his fans set to adjust from 0-100% according to CPU temp, with 100% fan speed being at 90C on his CPU.
How fast fans are running when using CPU temperature as the controlling curve datapoint
As you can see in the picture above, the moment Chad started his download, his CPU jumped to about 80C, and his fans are now in a tizzy because they think they need to cool it down as soon as possible. Now, if he had had an air cooler, that might have held some truth as the fan speeds would be directly connected to the air cooler that sits on the CPU, but even then, it would still take some time for the air cooler to soak up the heat from the CPU.
With a water cooled system, this process takes even longer, and the fans are much more efficient in dissipating the heat from the radiators. If you look at the graph you can also see that the coolant temperature has barely gone up 5 degrees, but his fans are still panicking and running at a very high speed, therefore creating more noise.
Now let's switch things around a bit. Instead of using the CPU temps to directly control the fan speeds, Chad has now set his fans to be controlled by the coolant temperature instead, with the max coolant temperature set to 45c.
Using coolant to control fan speeds - notice how even under heavy load the fan speeds do not rapidly change
As seen in the picture above, the fans now barely change speed since the coolant is very efficient in soaking up the heat and dissipating it. The coolant temperature is still around 35c as it was when we used CPU temps as a reference, but the fans are much quieter.
CPU temperatures are also the same, since it is the coolant temperature, and not the fan speeds that determines how cold the CPU is, so in the first scenario, the fans where actually running very fast for no reason at all.
So to summarize, using the CPU temperature as a target for the fans will make them think they need to run very fast, when in reality the CPU is cooled just fine, but without knowing the coolant temperature the fans have no way of adjusting for that.
This is also why when shopping for a new AIO CPU cooler you want to get one that measures the coolant temperature, and not just ask you to put your fans on your motherboard.
Now, with all this being said there still is a chance that your fans eventually will run at high, or even full speed. This is just determined on how much cooling capacity (how many, or how big of a radiator you have). So if you decide on getting an AIO CPU cooler, or go full out on a custom cooling loop, you will want to get as many radiators, or as big of a radiator as you can fit as it will directly correlate with how slow your fans can run while still keeping your CPU cool.
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