I'm planning on building a custom PC in a highly space-constrained case. I can't use a closed loop cooling kit because the motherboard I'm using requires a special CPU water block. Therefore, I must source all the components and build a custom loop myself.

All of the reservoir options I see out there are just a ton of overkill for the sake of looking really slick, but I don't care about any of that because nobody will be seeing it. And because the case is so tight, it's going to be extremely difficult to fit a reservoir, pump, and radiator in the amount of space I have to fit them in. Basically, I need to use the smallest volume of water I can get away with.

I've seen some forums suggesting that a reservoir just makes things look neat and makes it easier to fill the loop with coolant. So my question is, can just the volume of water inside the block, tubing, and radiator suffice to keep the system cool? I'm speaking generally of course (I don't want this question to be too broad or asking for a hardware recommendation).

This computer will not be a gaming rig, so the GPU will not be part of the loop. It will primarily be doing CPU-bound tasks like rendering and virtualization, so I'll be using a 12-core CPU. I only plan to moderately overclock, since reliability is preferable to speed for this machine.

  • What kind of board are you using that it doesn't have a regular CPU cooler mount (which is usually the requirement for closed loop coolers). – Seth May 11 '18 at 16:53
  • It's an Asrock X299E-ITX board. The component placement is non-standard and the risers prevent air-cooling from a side-mounted fan. Bitspower makes a custom water block designed specifically for this board, which I will need given that I only have 90mm of vertical height for cooling, which is not enough for a heatsink and downflow fan. – Wes Sayeed May 11 '18 at 17:01
  • Likely that one? Don't forget that you will need to attach fittings to that and run your tubing. You will likely be looking at least at another 30mm. So you will likely at least hit 60mm. It seems kind of hard to find dimensions for the pump unit of closed loop coolers but you might actually be able to fit them in that space. – Seth May 11 '18 at 17:18
  • @Seth; Yup that's the one. The problem with closed loop coolers is the VRMs on that board also need to be cooled, and without a fan there would be no airflow over those. That particular water block is designed to cover the VRMs also. – Wes Sayeed May 11 '18 at 17:22
  • Maybe consider using a closed loop cooler and add some 40mm fans for airflow for those VRMs? Also with a small amount of water you will find that your loop will run hotter as there is less time for heat dissipation. What size of radiator are you planning to use? How do you expect to get air to/from the graphics card? – Seth May 11 '18 at 17:30

A reservoir is not necessary but it will be painful to fill and bleed the loop.

Just think about how you will top it off and get excess air (that usually still sits in some of cooling elements like the radiator) out of the loop.

In addition I don't know what kind of components you're looking at but reservoirs can be quite small if you take a pump and reservoir combo. Take as an example EKWB reservoir and pump combos.

EK-XRES 100 DDC 3.2 PWM Elite (incl. pump)

The image is from a EK-XRES 100 DDC 3.2 PWM Elite combo. Which is just 65 x 68 x 138 mm (W x D x H).

  • It's going to be difficult to bleed the loop for sure. I've actually seen that combo unit, but it's 138mm high. I only have 90mm of vertical height to work with. I found this combo unit from Swiftech, but even with that I will have to hack-mount the fan to the exterior of the case to get it to fit. – Wes Sayeed May 11 '18 at 17:07
  • At that size just consider getting a bigger case. You're not going to get much joy out of that setup. From what you're saying you're looking at some excessive heat (12 cores and high load + pump + graphics card?) on a very limited space. What kind of case are you trying to cram this into? Doesn't it have a bay area or similar where you could place the pump and/or res or did you consider placing it outside of the case? – Seth May 11 '18 at 17:25
  • I'm not planning to cool the GPU with it since this is not a gaming rig. Although now that I think of it, adding an unnecessary GPU block to the loop would increase the volume of coolant without adding another significant heat source. But anyway, it's a custom mini-ITX case with a carrying handle. I call this thing a "Rack-In-The-Box" :-) It'll basically be a plug-in portable data center with a ton of virtual servers running on it. – Wes Sayeed May 11 '18 at 17:39
  • Your GPU is still going to produce heat. If you don't move that at some point you might be looking at a dead GPU. Obviously it depends on how you design your system. You will likely need some form of active cooling besides your PSU. Your radiator coolers might be sufficient but as said it depends on your setup. If it's a custom case just add that bit of space for the res at the bottom (you can lay them sideways) and don't take a combo but instead run them separate. – Seth May 11 '18 at 17:50

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