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How To Choose an All-in-One CPU Water Cooler

By Nathan Edwards

Last time we talked about air and liquid cooling options for your PC. This time we'll dig a little deeper into all-in-one liquid cooling loops, the middle ground between air coolers and fully custom liquid cooling loops.

Welcome back, deep divers. Last week, we talked about air and liquid cooling options for your PC. This time we'll dig a little deeper into all-in-one liquid cooling loops, the middle ground between air coolers and fully custom liquid cooling loops.

I mentioned that a good liquid-cooling loop will have better performance than all but the best air coolers, but Tested member Sweetz brings up an excellent point:

The thing about the closed loop coolers is that they have smaller thermal range and nonlinear cooling performance as compared to air coolers. Meaning that at CPU idle, when not stressed, they'll generally produce higher temperatures than competitive air coolers. However, when stressed, they can produce lower temps than the same air coolers that outperformed them at idle - again because they have a different thermal performance curve vs air coolers. You have to get used to this quirk when comparing them to air coolers. Ultimately, I believe lower highs are better than lower lows.

Large radiators do allow lower fan speeds than the entry level models, but the entry level models already allow lower fan speeds than many air coolers in the same price range. Given that air coolers in the same price range is what they'll be shopped against, I'm not sure I see their noise levels vs larger, more expensive water cooling systems as an argument for not buying the entry level models.

Choosing a cooler has a lot to do with your specific case. The all-in-ones with the best performance also have the most radiator area, and they won't necessarily work with every case. If you're building a new computer, of course, you get to choose a case and cooler at the same time, so make sure they're compatible.

Let's dive even deeper into the world of all-in-one coolers and discuss the nuances of radiator placement and airflow.

Case Compatibility and Radiator Placement

All else being equal, the bigger the radiator surface area, the better the cooling. Entry-level liquid coolers have radiators the size and shape of a 120mm case fan--roughly 120x120mm, and 25mm thick. From there, you can go bigger or thicker or both.

A 120 or 140mm radiator is designed to mount in place of your rear exhaust fan, and is the easiest to incorporate into an existing build, since the vast majority of chassis have a 120mm fan mount in the back. Entry-level 120mm loops include the Corsair H50, H55 and H60, Cooler Master Seidon 120M, and many more.

Photo credit: Flickr user immortalkenny via Creative Commons

140mm radiators, like those on the NZXT X40 or Corsair H90, have slightly better performance than entry-level 120mm radiators, and the 25mm thickness means they won't interfere with the rest of your components any more than a 120mm radiator will. The disadvantage is that fewer cases have 140mm rear exhaust fan mounts.

Another option, before you get into multi-fan-sized radiators, is to get a cooler with a thicker 120mm radiator. These coolers, like the Cooler Master Seidon 120XL, Thermaltake Water 2.0 Pro, Corsair H80i and Antec Kühler 920, have radiators that still fit in a 120mm fan slot but are thicker--the H80i's radiator is 38mm thick, while the Antec's is a whopping 49mm. These coolers usually ship with two fans--one for each side of the radiator, to help air move through the thicker radiator. So if you go with one of those, it'll take up more space inside your case.

If I were getting a liquid-cooling loop, I'd get the Corsair H80i. Maximum PC loves it, and as Dustin Sklavos notes in his AnandTech roundup, it outperforms some 140mm and 240mm radiators, but it's more likely to fit in your existing case, since it uses a 38mm thick 120mm radiator and two fans rather than a rad with a single fan. It's around $90--the same as you'd spend on a top-of-the-line air cooler. A thick 120mm radiator is a good sweet spot for all-in-one water cooling.

A 240mm or 280mm radiator is designed to mount where your case's top exhaust fans would normally go--provided your case has two 120mm or 140mm fan mounts there. Many enthusiast cases support a 240mm radiator; fewer support a 280mm radiator. Check your case for compatibility, and note that even if it has two 120mm or two 140mm fan mounts on top, that doesn't necessarily mean the mounting holes are spaced correctly for your radiator. Check the manufacturer's websites to see; note that some (ahem, Corsair) only list cooler compatibility with their own cases, not anyone else's. If you can't find that information on the manufacturer website, google the name of the cooler you're thinking of, along with your case, to see if someone else has gotten it working.

At the high end of the all-in-one spectrum, the NZXT Kraken X60 and Corsair H110 have been getting stellar reviews--it looks like they're the best all-in-one systems you can buy right now, but those 280mm radiators mean that they're unlikely to fit in most cases, and they're expensive, at $130-140 each. Their massive surface areas mean that they cool better at low fan speeds than other liquid coolers do at high speeds. To paraphrase Ferris Bueller, if you have the means (and the case), we highly recommend picking one up.

Optimizing Airflow

Airflow is a trickier subject than you might imagine, with different manufacturers recommending different orientations. There are a couple of things to keep in mind: your case's existing airflow, and the parts of your rig that aren't water-cooled.

Keep in mind your case's existing airflow, and the parts of your rig that aren't water-cooled.

If your radiator fans are mounted as intakes, the air that flows over your radiator fins will be cool air from outside your case, while mounting the fans as exhaust pulls already-warmed air from inside your case out of it. Both have their advantages (and the internet is littered with fierce partisans extolling the virtues of each), and which you choose will largely depend on your case's existing airflow scheme and the size of the cooler you get.

(There's another, related debate as to whether it's better to have positive or negative air pressure in your case. As I mentioned in part two of my series on cases, I'm on Team Positive Air Pressure, with one caveat: all of your intake fans should have dust filters that are easily removable for cleaning.)

A 120mm radiator is the easiest to incorporate into your existing airflow, since it mounts in place of a fan that's already designed to be exhaust. Keeping it an exhaust fan means that you don't have to rethink your case's cooling setup.

240mm radiators are trickier--many manufacturers advocate mounting them so that the fans pull air into the case. This has the benefit of pushing cooler air over parts of your motherboard, like the voltage regulators, that don't get as much airflow with a liquid cooling setup as they would with an air cooler on the CPU. The drawback is that mounting intake fans where the case manufacturer had put exhaust fans can screw with the airflow plan, and since those fan mounts were originally designed to be exhaust, they likely don't have dust filters on them. If you plan to mount your top cooler's fans as intakes, get some dust filters for those intakes.

On the other hand, mounting two exhaust fans where your existing case had one or none can turn a positive airflow situation into a negative one, sucking dust into your case through every hole and vent in the case. You may need to add another front intake fan to keep your net intake greater than your exhaust and keep positive air pressure in your case.

What about GPU Liquid Cooling?

In the research for this piece I came across a commenter raising a very good point: "I find it hilarious that there are so many CPU watercoolers for chips that just don't need them, yet we have air coolers on graphics cards that need to dissipate 300W in a cooler the width of only two card slots."

Unfortunately, there aren't as many options for all-in-one GPU liquid cooling loops as there are for CPUs. Arctic sells the Accelero Hybrid VGA, an add-on liquid cooler that supports a wide range of GPUs--AnandTech reviewed it and called it a "powerful weapon," though with a tricky install process and a $170 price tag it's not for everyone.

A website called TripT sells custom mounting brackets and backplates to let you use any Asetek-made liquid-cooling loop (which is nearly every liquid-cooling loop from Antec, Thermaltake, NZXT or Corsair except Corsair's H60, H80, and H100 series coolers) to cool your GPU instead. If you're feeling adventurous you could give that a try.

Other than that, you'll need a full custom loop if you want to liquid-cool your GPU. The good news is that you can find custom waterblocks for nearly every GPU on the market at sites like FrozenCPU and Performance PCs.

Something in the Water

An all-in-one liquid cooling loop can be a quieter alternative to a massive air cooler, and has the added advantage of not hanging several pounds of aluminum from your motherboard. It also requires zero maintenance and is relatively easy to install.

Do you use an all-in-one loop? What do you like about it? What don't you like? Sound off in the comments below!