There’s a general perception that custom loop liquid cooling is directly superior to all-in-one liquid coolers like our Hydro Series line, and for many enthusiasts, all-in-one liquid coolers aren't “true liquid cooling.” It’s understandable why enthusiasts would think so, but it’s not factually accurate. The reality, as it so often is, is much more nuanced.
The essential components of liquid cooling in a PC are: a pump, a waterblock, a radiator, and coolant. Custom loops will add a coolant reservoir or two, but this isn't strictly necessary, just incredibly convenient and useful for building and maintaining the loop. So if we define liquid cooling on these terms and leave the reservoir as optional, then all-in-one liquid coolers absolutely count. The pump is integrated into the waterblock, connected to a radiator, and the loop is then filled with coolant and sealed at the factory. From a purely technical perspective, there just isn't much difference between a custom loop and an all-in-one cooler.
Where the custom loop comes out ahead is in a couple of places. Custom loops tend to use copper radiators to go with their copper waterblocks, and the pumps tend to be more powerful. That makes sense: CPU waterblocks with integrated pumps are fairly rarefied, with Swiftech’s Apogee Drive II being the most notable example. Incidentally, their popular H220 is less a purpose-designed all-in-one cooler similar to our Hydro Series products and more just a combination of their Apogee Drive II, one of their 240mm radiators, and two of their Helix fans. They pretty much just made an all-in-one cooler using off the shelf (off their shelf) parts.
The copper radiator is an important component, as is the oftentimes more powerful pump used in a custom loop. But keep in mind that more powerful pump is a necessity for a custom loop: an all-in-one only needs to push coolant through a single CPU waterblock and a radiator, but a custom loop will typically have the CPU waterblock, at least one or two GPU waterblocks, and more than one radiator. As for the radiator, a copper radiator becomes more relevant when you’re dissipating more than just a single source of heat. For the purposes of an all-in-one like the Hydro Series, a copper radiator simply isn’t necessary; it’s added expense with questionable tangible benefit to the end user.
The highest TDP processor available is an AMD FX-9590, at 220 watts. Overclock it some more and you may hit 250 watts. But that chip is also an outlier; Intel’s TDP tops out at 150 watts with 8+ core Xeons. Simply put, an all-in-one cooler just doesn't have to dissipate that much heat, and the name of the game is more of just how efficiently and rapidly heat can be pulled from the CPU and dissipated. That’s something we have a serious interest in and continue to invest time and resources in researching.
Where the custom loop becomes more relevant is in cooling graphics cards. We’re not going to produce a graphics card bracket for our all-in-one coolers unless we’re convinced we can properly cool both the memory and the power circuitry on the PCB, and this is one of the chief benefits of using a custom loop. Waterblocks for graphics cards typically cover the entire PCB or at least all of the heat generating components, improving longevity and allowing power circuitry to run cooler and more efficiently.
As for the GPU itself, just putting it under water can cut load temperatures in half or better. The flip-side of a custom loop is that it requires tremendous work and expense, and if you’re only interested in cooling the CPU, it’s just not worth it. The gains over a high end all-in-one cooler like the Hydro Series H100i or H110 are modest if noticeable at all, and I can tell you if it wasn't for the graphics cards in my loop at home I’d probably go back to using an all-in-one for my CPU. A custom loop requires care and maintenance on top of the expense, while all-in-ones are sealed systems designed to be maintenance-free for extended periods of time.
It’s also much harder to upgrade or even do maintenance on the computer itself. SATA ports have started to fail on the motherboard in my home loop; I've had to manhandle the system a few times and risk leaks just to rotate cables into different ports, and that’s ignoring the fundamental issue of potentially needing to replace the motherboard. There’s also the fact that I have a propensity for building and rebuilding my own system whenever a new component looks at me funny, and that’s suddenly been curtailed. An all-in-one is easy to install and remove, but a custom loop can be a nightmare.
Ultimately, from a pure performance perspective, if you have a very high-powered machine (high end CPU, multiple graphics cards), building a custom loop can make sense. But if you’re gunning for a more modest, single graphics card build, you can get a quiet and efficient system just by using a good all-in-one CPU cooler and a graphics card with a custom cooler design without worrying that the CPU cooler is limiting overclocking potential. And even if you’re going multi-GPU, cards with good blower style coolers (NVIDIA’s reference coolers on the 770 and up are incredible) may be just fine.