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CPU Water Cooling FAQs

By Joe Citarella from Overclockers.com with permission

Overclockers spend a lot of time on cooling and with good reason - we all know heat is the enemy to speed. As speeds increase, the need for efficient cooling escalates, especially with peltiers and super-cooling. Air cooling can only take you so far and at some point water cooling has to be considered. What follows are some basics to consider:

WHY IS WATER COOLING BETTER?

Air can only carry away so much heat; the more heat you want to dissipate, the more air flow and surface area you need for a heatsink. Diminishing returns starts to set in fairly rapidly once you get beyond the Alpha heatsink stage. No matter how large the heatsink, its contact point is still the CPU's slug. As heat moves beyond this contact area, it encounters something called "spread resistance". The reason you see copper bases in some heatsinks is that copper is more efficient in spreading heat over its surface than aluminum, but only up to a point.

So if the task at hand is to get as much cooling concentrated in a given area, all things being equal the more efficient "dissipating medium" (i.e. air or water) will cool better than its inferior. In the case of air vs. water, there is no contest - water is way better.

WHAT PARTS DO I NEED?

It's the same setup as you have in your car - a radiator, fan, heat exchanger and pump. All thing being equal, the larger the radiator, the more cooling; the higher the water flow through the system, the more cooling; and finally the more surface area contact between the heat exchanger and CPU, the more cooling. As in all things, diminishing returns - you should size components to the task at hand. You could use the radiator from your car but don't expect massive gains - diminishing returns sets in pretty quickly.

WHAT ABOUT HOSE SIZES?

This is something that should be planned out before you buy components. If you buy a kit, everything should fit so there's no problem. If you build your own, make sure that the connections are all the same size. If for example you buy a Senfu radiator with 2 mm fittings and use it with a pump that has 3/8" fittings, you have to improvise a "reducer" between the two.

I have run into this in testing different gear and ready-made solutions are few and far between.

WHERE DO I GET THE PARTS?

Some folks are now selling complete kits for about $100. Most will do fine and we will review as many of these as we can. If you want to roll your own, check out the parts listing HERE. You will have to consider the dimensions of your case and where you want to mount the radiator.

WHERE CAN I BUY KITS?

The most critical element in all this is the water block; buying it from one of these sources is the first step. There is a performance difference between copper and aluminum blocks, but it is arguable whether this is a meaningful difference considering how effective water cooling is overall.

WHAT SHOULD I LOOK FOR IN A PUMP?

I think the most critical factor is the pump's ability to lift water to a certain height - this is called "head". Gallon-per-hour of liters-per-hour figures can be misleading; if a pump cannot lift water over one foot, then having this pump in a case where the pumping distance of two feet will not work. This has been the problem with the pumps sold as part of the Senfu kit.

At a minimum, a pump should lift water to three feet at something like 20 gph. This should be sufficient for any CPU cooling.

WHAT SHOULD I LOOK FOR IN A WATER BLOCK?

Pay close attention to how they mount - these are all custom designed fittings. Note what hose size is required and if it fits with the other components. Physical size is less important than water flow - hose size is an indication of how much water gets pumped through. Copper is a better heat conductor than aluminum but will be more expensive.

WHAT SHOULD I LOOK FOR IN A RADIATOR?

Size depends on your cooling requirement. If you plan to use multiple peltiers, then look for a good size radiator - say something like 5x10 or larger. How big will depend on where you plan to mount it; internal mounting does place a premium on size.

For internal mounting, anything over 5x7 gets tricky. Also consider what size fan you plan to use - 120 mms are the best for air-flow and low noise.

WHERE SHOULD I PUT THE RADIATOR?

Here's where ingenuity comes in; you could:

Mount the radiator in the case's front, using the fan to pull air over the radiator and into the case: Mount the radiator at the top of the case, exhausting air out of the case through the radiator; Mount the radiator outside the case, running hoses outside the case to a stand-alone radiator housing. I'm sure there are other options to consider - it's a question of what you're trying to accomplish.

OK, I WANT SUPER COOLING - HOW?

This gets you into water cooled peltiers. I won't go into peltier considerations here, but there will be a lot of waste heat from peltiers. You might want to consider an external radiator as a lot of heat could wind up in the case unless you mount the radiator at the top of the case exhausting heat.

The next consideration is water temp - if you want real super cooling, you don't need a radiator - you need a bucket full of ice water. This is actually simpler - just the pump, heat exchanger and peltiers. Of course you need a lot of ice if you plan to use this on a continuous basis, so access to an ice machine would be nice.

WHAT ABOUT NOISE?

This is for me the best part - I use a single 120 mm fan to pull air into the case and through the radiator and a 92 mm exhaust fan in addition to the power supply fan. All fans are low noise models. This setup is considerably quieter than any CPU air cooling and results in my CPU temp at rest 2-4 C below ambient and under stress (Prime95) 5-7 C over ambient (PIII 600E). Coupled with a low-noise power supply, it is almost a whisper.

WON'T THE PUMP MAKE NOISE?

Depends on the pump and how you mount it. Cheap pumps are noisy, and mag-drive pumps are noisier than shaft drive pumps. You will need a water container to house the pump as they are not in-line models - they run submerged. I placed foam insulation under the pump container to further isolate noise and I can not hear the pump running (with everything else off) more than three feet from the case. And if you hear it, it is low frequency sound.

Plan to spend about $20-$30 for a good pump - you won't regret it.

WHAT ABOUT MAINTENANCE?

In a closed loop system, maintenance is minor. Maybe once a month make sure the water level is OK (should be no evaporation) and that's about it. Good pumps are designed for continuous running, are guaranteed for two years and require no maintenance.

AND IF THE PUMP FAILS?

Not much different from a fan failure. If you take precautions, you can minimize the chance of catastrophic failure:

Use a CPU idle program like Waterfall - at rest there is almost no heat generated; Use a monitor program like Motherboard Monitor - you will know if your CPU starts to overheat very quickly and you can link to a shutdown routine. Preventative Maintenance: Change out the pump every two years. Extreme Caution: Use two pumps in tandem. BUT WATER IN ELECTRONICS! WHAT ABOUT A LEAK? Well if you're real concerned you can take some preventative measures: Waterproof all the boards, use die-electric grease in all the card and slot 1 connectors and use distilled water. But let's face it - this is not a high-pressure system, so pressure leaks should not be an issue. If every connection is clamped and proven in, the chance of a catastrophe is minimal (right Mr. Murphy?).

The above FAQ is used here with permission by Joe Citarella from Overclockers.com.

Related Items: | Overclocking - Introduction | Watercooling Products | Case Mods |

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