CPU Cooling Primer

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Heat is the enemy. It really is that simple – computer chips degrade with heat and the more heat, the more likely you will experience performance problems. One of the most critical components in your system is the CPU cooler. What follows are some observations on various cooling solutions and the results you can expect, listed in order of increased cooling potential.

Heatsink Basics

A heatsink’s performance is the result of two critical factors – surface area and air flow. All other things being equal, a heatsink with more fin surface area will outperform one of lesser area, and an active (i.e. cooled by a fan) heatsink will outperform the same design without a fan. If you keep these basics in mind, choosing an effective CPU cooler among the many offered is one step easier.

CPU Basics

The performance rule is very simple – the cooler a CPU runs, the faster its operating speed. A CPU which runs at 300 MHz at room temperature might run at 600 MHz if it is cooled down to -50 C. A CPU running at 30 C over room temperature will not run be as stable as one running at room temperature. Heat affects performance adversely. CPUs are designed to perform within spec within a given temperature range and operating the CPU outside of these ranges will either fry (upper end of range) the CPU or increase its performance (lower end the range).

OEM CPU Coolers

OEM ship manufacturers may ship chips with their own cooler. It is designed to work within the range of the chip’s specs. If all you will do is run the CPU at spec and within normal ambient operating temperatures, the OEM cooler is perfectly adequate. Repeat, adequate, not great. For example, I am not aware of any OEM unit that comes with two fans. The more airflow, the better the performance; however, cost is a big constraint for chip manufacturers and if one fan will do it, then it will ship with one fan. Yes, some have overclocked CPUs with OEM coolers; in my book, this is not a prudent long term solution.

Cost: Included with CPU
Cooling: Room Temperature + 10 to 30C

“No-Name” CPU Coolers

If you go to computer shows or buy a cooler locally, most likely you will see a lot of unbranded or no-name coolers. These can be effective if you stick to evaluating them on the basics – fin area and air flow. However, these tend to be cheap units (probably not costing more than $3-5 wholesale) and are sold or packaged in cost competitive systems. They will do the job if you don’t exceed system design specs. Don’t expect superior performance or be surprised if you push the system out of spec, it blue screens. Nothing will bring a system to instability quicker than a hot chip.

Cost: $10-$25
Cooling: Room Temperature + 10 to 30C

Branded CPU Coolers

The third party (branded) market offers CPU coolers that are (mostly) well designed and marketed to users searching for efficient cooling solutions. Within this segment are some brands that are notorious for offering copy-cat designs and sup-par performance, hoping that flashy marketing copy will suffice. If you only buy one heatsink and rely on ad copy, you may come up short and never know it. Fortunately for users looking for the best, there are a number of hardware sites offering evaluations based on real world testing – just check out Cool Links for some of them.

In my experience, heatsinks from Alpha, Global Win, TennMax and Vantec are usually at the top of the performance rankings, although individual units will, of course, vary. Alpha is a performance leader and tough to beat, although Global Win has taken on the challenge and offers a competitive unit (FDP32) to Alpha’s socket 7 cooler. Alpha raised the performance bar and we should see more high-performance designs on the market.

CPU coolers in this category can make the difference of attaining overclocked speeds or not. Even if not overclocking, more efficient cooling simply is better for the system long term. The best performance you can expect from these coolers is for the CPU to operate at close to room temperature.

Cost: $15-$60
Cooling: Room Temperature +2 to +15C

Peltier Coolers

The CPU coolers up to this point are air cooled. A major step up in performance is the Peltier CPU Cooler. This design incorporates a ceramic package of chips which acts like a miniature refrigerator – it pumps heat away from the chip; one side is cold, the other hot. This requires a heatsink on the hot side to dispose of the heat moved away from the CPU. Peltiers can result in lowering the chip’s operating temperature to below ambient temperatures, allowing more overclocked speed compared to an active non-peltier heatsink.

That’s the good news – the bad news is that Peltiers are very tricky to operate and require careful attention to insulation. Since Peltiers can operate at below room temperatures, condensation can form on the unit if not properly insulated. Many commercial Peltier units are inadequately or not insulated at all and might result in water damage. Consequently many commercial units are designed to cool chips to room temperature at best and as a result are under powered. Before buying a commercial Peltier unit, carefully read any available reviews on the unit – if none are available, buy at your own risk.

Cost: $25 – $400
Cooling: Room Temperature -10 C

Water Cooling

So far we have been talking about air cooled solutions. Water cooling is inherently more efficient due to its superior ability to absorb heat. The drawbacks are obvious – you need a water jacket to attach to the CPU, a pump, a water source and a cooling source to cool the water (assuming you are not using running water). In addition, you will most likely need insulation as condensation be an issue.

Water Cooled Peltiers

Arguably the most efficient performance alternative, water cooled Peltiers have dropped chip temperatures to the -50 C range. Performance gains have been considerable, with 100% gains in speed not uncommon. However, these setups must be classed as experimental and for the die-hard performance enthusiast seeking to push the performance envelope into new territory. These experiments are instructive in demonstrating the chip’s inherent overclocking potential.

Cost: $100 – $300
Cooling: Room Temerature -30 to -60C

Liquid Nitrogen

Some pushing the performance envelope claim to run chips in liquid nitrogen, resulting in super-cooled temperatures. I take these with a grain of salt – this is way out stuff and difficult to document unless actually seen. It is of course possible, but not at all practical.

Cost: Considerable
Cooling: Room Temperature -100C

Refrigeration Units

Some intrepid souls have taken refrigeration units from other uses (e.g. dehumidifiers) and adapted them to super cooling CPUs. This is an elegant cooling solution but considerably more difficult to accomplish – if you are not handy with tools, this is not your thing.

There are two commercial manufacturers of cases which incorporate small refrigeration units in the case. These units attach a cooling coil to the CPU resulting in sub-zero CPU temperatures with consequent performance gains. ASETEK and KryoTech are currently the two providing this solution. These solutions are costly (>$1,000); whether the performance gains are worth the expense is questionable; as CPUs are introduced at increasingly higher operating speeds, what was once pushing the envelope becomes off-the-shelf in 6-12 months.

Refrigerated units also come in less costly versions (<$500) which are designed to keep CPUs at room temperature. I have a KryoTech Renegade PE and have never seen the internal diode temperature of any CPU go above 85 F. The advantage its ability to achieve this without considerable fan noise - it is quiet, consistent and a long-lasting solution - my personal favorite.

Cost: $400 – $2,000
Cooling: Room Temperature to -50C

Total System Immersion

I have seen one instance of someone immersing the motherboard into a cold non-conductive solution (mineral oil), with the oil cooled by an air conditioner. This is about as far out as one can get in chasing demon heat.

Cost: ?
Cooling: ?

Conclusion

Which cooling solution works best for you depends on your objectives; however, the basics remain – the cooler, the better. The best active air-cooled CPU coolers are among the branded units, Peltiers are better but require careful selection, and refrigeration units (in my book) are the best long term cooling solution. I am sure someone will come up with a different approach or some combination of solutions which is what makes keeps this whole area so interesting.


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