Should H115i Fans Be Running at 100% 24/7?

Hi All. Just built a PC gaming rig and used the Corsair H115i for my AIO CPU cooler. I'm using an Asus Z270E motherboard and Intel's i7-7700K CPU. I'm also using Phantek's Entro Evolv (Tempered Glass) case. I'm not currently overclocking the system, but I have plans to do so in the near future.

My question relates to the fan speeds on Corsair's H115i AIO Cooler. Right now the two 140mm fans are running at a constant 100% (about 1,400 rpm) 24/7 and are a bit loud at that speed. I have the H115i plugged into a motherboard header which reads AIO_Pump. When I go into the Asus BIOS, I see that it's a PWM device; however, I'm not able to assign a profile (like the case fans) which would modulate the fan speed at various temperatures; rather, it's set to a static 100%.

This is leading me to believe that the AIO_Pump header may not actualy be a PWM. So my first question is this: Do I want my H115i to be PWM modulated? Does plugging it into a PWM header such as CPU_OPT or perhaps into the case's 6-Fan Controller Hub (the hub plugs into CPU_FAN) present risks to the processor? Especially, considering I'll be looking to overclock the system within the next few weeks?

Another possible solution would be to manually set the AIO fans at something like a static 80%.

I'm nervous to mess around with the CPU fans because I don't want to toast the CPU. I know the website states the fans (i.e. the two SP140L) are PWM modulated and can be tweaked, but I've also heard that you don't want to mess around too much with this. Any expert advice would be greatly appreciated.

Sorry for the long post!

Well good news and bad news. The bad news is those fans actually max out at 2000 rpm, so you still have some headroom and noise left over. The good news is you likely have an easy fix for this.

If you plugged the fans into the pump block as the directions indicate, then you can only use the Link software to regulate the speed of the pump AND fans. You cannot control the fans or pump from the BIOS or other software control and the power for both comes from the SATA connection. The 'dummy' motherboard lead plays another purpose and that 1400 rpm you see is one half the pump speed. Pumps and fans turn differently and you need a divider/multiplier to turn back into a normal value, in this case 2. Open up Link and click on the pump and fans in the "H115i" box on the right. Link will show you the proper speeds for both and offer control options, including fixed percentages. The default control variable is coolant temperature (H115i Temp) so keep that in mind when looking at the preset curve options. It will take a little while to learn your range.

You cannot toast the CPU no matter what you do with the fans. That is the big advantage of water cooling. The heat is transferred off the CPU through the cold plate and into the coolant stream. That is a secondary holding tank for the heat, waiting to be expelled as it passes through the radiator. No radiator that fits in a case can take out all the heat in one pass, so the liquid/coolant temp will build slightly when under load. This is what you use to regulate the fans. A +6C rise in coolant temp means the most you can possible reduce CPU temp at any fan speed is also 6C. On a 7700K you will see high CPU temps when overclocking or doing silly things like running Prime 95. However, that will all be voltage based on the coolant delta will still be low. You can get away with 1000 rpm max for most everything. My CPU pulls about 205-215W at full draw and I can use 1350 rpm on a 280mm. You have a lot less wattage to get rid of.

Well good news and bad news. The bad news is those fans actually max out at 2000 rpm, so you still have some headroom and noise left over. The good news is you likely have an easy fix for this.

 

If you plugged the fans into the pump block as the directions indicate, then you can only use the Link software to regulate the speed of the pump AND fans. You cannot control the fans or pump from the BIOS or other software control and the power for both comes from the SATA connection. The 'dummy' motherboard lead plays another purpose and that 1400 rpm you see is one half the pump speed. Pumps and fans turn differently and you need a divider/multiplier to turn back into a normal value, in this case 2. Open up Link and click on the pump and fans in the "H115i" box on the right. Link will show you the proper speeds for both and offer control options, including fixed percentages. The default control variable is coolant temperature (H115i Temp) so keep that in mind when looking at the preset curve options. It will take a little while to learn your range.

 

You cannot toast the CPU no matter what you do with the fans. That is the big advantage of water cooling. The heat is transferred off the CPU through the cold plate and into the coolant stream. That is a secondary holding tank for the heat, waiting to be expelled as it passes through the radiator. No radiator that fits in a case can take out all the heat in one pass, so the liquid/coolant temp will build slightly when under load. This is what you use to regulate the fans. A +6C rise in coolant temp means the most you can possible reduce CPU temp at any fan speed is also 6C. On a 7700K you will see high CPU temps when overclocking or doing silly things like running Prime 95. However, that will all be voltage based on the coolant delta will still be low. You can get away with 1000 rpm max for most everything. My CPU pulls about 205-215W at full draw and I can use 1350 rpm on a 280mm. You have a lot less wattage to get rid of.

Thanks a lot for that info. Learned some good stuff there. Primarily your point about the coolant itself being a secondary holding tank for CPU heat generation and the 280mm fans only having an indirect effect on CPU temp at best. Not to mention your point about the BIOS having no control on these fans. And yes, I do have both 140mm fans plugged into the pump as specified in the manual.

You lost me a bit with your final comments regarding voltage and coolant delta (sorry I'm new to this). Are you saying that the additional heat in the CPU caused by overclocking arises due the additional voltage draw by the CPU rather than the actual additional processing taking place? And when you use the term "coolant delta" does that refer to the factor by which the coolant temp changes?

Bottom line, I should be able to go into LINK and slowly tweak my fans down while keeping an eye on the coolant temp, right?

Yes, you should be able to do all your tweaking through Link. If for whatever reason you decide you don't like this or do not want to run Link, move the fans to your CPU/OPT headers, leave the H115i lead on AIO_PUMP, and then set the fans from the BIOS or other normal fan software controls. That will limit you to CPU temp as the control variable, but other than overly dynamic fan changes, it works fine.

I didn't really need to bring up the coolant delta and voltage limitation, but when 7700K launched there was a flood of "my cooler isn't working" posts, mostly right after running Prime95 or IBT while on the Auto adaptive voltage. Kaby auto voltage is very adaptable and it will pour it on if you let it. Most people will want to set a specific Vcore in the BIOS, even if they keep the stock clocks. That isn't really new, but a stock Kaby can hit 80C+ running any stress test if it is allowed to use 1.40v. That's a whole lot more than you need.

Pretty much all modern CPUs are going to be voltage limited. The voltage necessary to run a specific clock speed will create too much on the spot heat -- more than the CPU material can effectively transfer out instantly. All that heat on the pins' side has to pass through the CPU medium before it can reach the cold plate and water stream. The H115i itself is capable of getting rid of twice the wattage you could ever reach on any overclock. The problem is the voltage will melt the silicon before you get there. This is why extreme overclockers lower the starting temperature of the CPU with liquid nitrogen and don't use gigantic 8ft tall radiators.

Yes, coolant delta refers to the difference between your starting and load (or current) H115i Temp. This is the value affected by fan speed. it is case and power setting specific, but most people will have an idle coolant temp of 4-7C above their room temp and see loads coolant temps of +6-10C higher than that. It is a really common mistake to use too much fan speed when coming from an air tower (with almost no heat holding capacity) to water. I can turn my fans off and not hit the limit for a while. Further still, if I hooked a pump into a 100 gallon fish tank full of water, I don't need fans or a radiator at all. I just keep the flow going and the heat naturally dissipates back in the tank. Not quite a 100 gallons in a 280mm cooler, so you do need fan speed -- but not a lot. Moving the fans from 800 to 1400 might bring your coolant temp down 2C. That means the CPU temp will also drop by 2C (coolant temp is the baseline as theoretical lowest possible CPU temp). However, most people would consider that level of fan noise a bad trade for a measly 2C decrease. The nice thing about a 280 is the larger surface area lets you use relaxed fan speeds. However, because room temperature has such a strong effect on your starting coolant temp, those preset curves may not be useful depending on your season. They are more or less based on a standard 20-23C room temperature, but in Summer many of us go above that. It would not be unusual to have an idle coolant temp of 35C on a hot day. That does not mean you need 1500 rpm fans at idle since you cannot go below that 35C no matter what. This is why most people will ultimately want to make their own custom curves, once they become accustomed to the normal range of coolant temperatures.