680X + H100i Platinum SE + 2080ti AIO

Hi guys, just wondering your thoughts on fan directions for the two AIOs. One will be mounted top and the other bottom. There are the three intakes in the front and 1 exhaust in the rear. My initial thoughts are to mount the CPU AIO top as exhaust, and the GPU AIO bottom as intake. Pulling air from the front and bottom then pushing it out the top and back makes sense. I don't think the air flowing over the top AIO rad would be very warm with this setup, but I'm looking for advice.

 

Also it's been a while since I did a new build. Should I replace the factory thermal paste for the MX-4 I have on hand? Thank you!

Edited July 11, 2019 by CenterFire

You have several options.

 

1) Front/bottom intake as you described. I am running this now with dual 280mm radiators in a custom loop. Surprisingly, you don't get a lot of extra heat into the top radiator from the bottom and the rear exhaust is warmer than either coolant temp exiting the radiators, heat is going out the right places. This should work fine for most people.

 

2) Top/bottom radiator intake, front/rear exhaust - It seems a bit odd, but turned out to be remarkably efficient. The distance from intake to exhaust is so short that warmer air goes straight out. The top intake seems counter-intuitive but forces heat coming off the VRM, RAM, etc. to go elsewhere, rather than through the top radiator. I do not filter the radiators when using them as intake. It's a noticeable hit in performance and I can dust it off every 3 months. I do have filters in place on some of the extra vent areas. With balanced fan control, the lower radiator will push heat right out the rear venting.

 

3) Front/rear intake, top/bottom radiator exhaust - I was worried about the bottom warm exhaust getting sucked back into the case through the front or rear. Never happened. Most of it blows out the sides and dissipates into the room, however the Air 740 has a different bottom with that same heavy contoured panel like the front. That may play a factor. This is the one for people who more hazardous or dusty/cat infested environments. You can filter the entire case up, with no need to cover the exhaust ports except perhaps when the machine is off.

 

I've run all these for months on a 740 with multiple fan types. For me it really is looking for tiny differences and the spread is only about 2C coolant temp from best to worst. 2C isn't going to matter. The factor that most often influenced a change was fan type. I have my HDs on now and they look good from both sides and have both decent radiator and airflow performance. Where I started to really fuss is when I used LL and ML fans. The LL obviously have a prettier side and you likely want to see it. However, I still prefer the backside of a LL to the ML. The ML-RGB fan does not shield its 4 LEDs from the rear, so you get a lot of light bleed. That was really annoying when using them as intake. So most often my fan choice then dictated the arrangement. All of these work.

 

There is one caveat. When I first got my 2080 Ti, I was still running separate cooling systems for the CPU and GPU. GPU was a single 280mm custom loop. CPU was H115i Pro. This is most similar to the position you are in now. Previously I had run a reverse flow case with rear/bottom intake, front/top radiator exhaust. Worked great. New GPU 5mm too long for the 740/680 frame. I suspect this is your problem as well. It's a bit of a long run to go around the GPU from the CPU block to a bottom radiator, so I did the natural thing of CPU rad top exhaust, GPU radiator bottom intake. My problem with this was on the single 280mm radiator, my GPU coolant was hitting 36-37C in the dead of Winter and that was heating up the entire case by about 5-6C more than I was accustomed to. I flipped it over and ran the bottom as exhaust and this was mostly better, but I didn't like the idea of blowing (predicted) 40C+ air into the wood underneath all Summer. This pushed me to make a dual loop and cut the overall coolant temps down. I am assuming you are using one of the 240mm AIO models for the Ti. I think you should expect coolant temps at 40-42C in the warmer parts of the year. Exhaust air temp will approximately equal coolant temperature. As long as you keep that moving out the back, you should be OK. It also may be less heat in the system since GPU VRM will be air cooled.

 

Now if in fact the GPU AIO is 120mm radiator, you want that on the back slot as exhaust. I have run this way as well with a Titan XP and CPU radiator top exhaust. That was one of the best set-ups. All the heat out, tons of intake potential with front/bottom let me keep those fan speeds lower. Really efficient. With a 120mm radiator, the Ti coolant is going to be near 50C and you don't want that air dumped into the case.

Edited July 12, 2019 by c-attack

Fantastic response, thank you very much for that. You are correct that the GPU AIO is also 240mm. The more I consider this the more your option 1 makes sense. 3 intake fans on the front supply cold air front to back. Bottom rad as an intake pushes warmer air up. This air will be pushed to the back from the intakes in the front where it should be exhausted out by the back exhaust mounted in the upper most position. This leaves the top rad as exhaust to suck the cool air coming from the front of the case. I think I'll try this first.

I agree and am running it now after doing #2 and #3 for most of the last three months. It allows some cooler air to come in over the RAM, the rear fan should take some of the socket area heat out the back rather than through the top radiator plus some of the lower radiator heat. Also, if you are going to do a case full of LL fans, this puts all of them except the bottom set with the light ring exposed to you. I've got temp probes every where and while the difference is slight, I reduced the air temp around the RAM by 2C and the same across the top layer of the case. That in turn took the coolant temp in the top radiator down 2C as well.

 

One thing to consider - you might want the bottom set of radiator fans in pull above the radiator. Even with a pretty good amount of clearance underneath, these are the ones that I hear the most. I am running push-pull 140s on the bottom and shut the lower set off when at the desktop. Those make the most noise. When it was a free air intake, I could run whatever at 1000 rpm and never hear it. The airflow characteristics change when you sandwich in between the case mesh and the radiator. However, I am being fairly particular about this. Many people might never notice, although since you are likely to be running them at a higher speed, there is a definite chance you would.

Edited July 12, 2019 by c-attack