*These test are no longer updated.
CPU cooling performance is based on CPU Die Simulator Test Results¹ for various CPU cooling solutions; some P4 tests are based on motherboard test results. The Die Simulator is a pure performance test which excludes secondary heatpath effects found on motherboards.
Comparing water cooling kits and cases are system specific – you can not infer from these tests that waterblock A is better than the waterblock B. You CAN conclude that the components in kit/case A perform better than the kit/case B based on test C/Ws.
However, especially with a kit, performance in a consumer’s case can vary from these results. For example, if you place the radiator in a case with restricted airflow, you will not achieve the performance levels shown below. Note also that changing components will impact results – if you substitute an inferior (or better) waterpump for an EHEIM, you will not see these results.
Watercooling components tested by Overclockers.com use test gear and methods as outlined in Waterblock Testing: Mounting.
In evaluating a purchase, the Relative Rankings are more important than the absolute C/W. For potential motherboard performance, clicking on a name links to its full test results².
Also note that air cooling heatsink fans are as they are sold; some stock fans are underpowered and replacing them with a Delta 38 or more powerful fan will improve results. However, noise levels will noticeably increase, as will cost, if another fan must be purchased. Factors such as noise, motherboard performance and the impact of higher speed fans may be found in the reviews.
Readers are cautioned that Delta 38 and other fans with cfm ratings >30 are found by many users to be objectionably loud; a number have abandoned these fans after a short time. “Loud”, as measured by a Radio Shack Sound Meter 8″ from the fan’s intake, measures 69-70 dBA while “Moderate” measures 62-63 dBA, about as loud as a 26 cfm YS Tech.
Sidewinder Computers has sound files for most of the fans you’ll encounter HERE. “All fan sounds were recorded in MP3 audio format (128kbps bit rate; 44.1kHz sample rate) and are ranked by apparent loudness. To hear them, you must have an MP3 player installed, such as Winamp, Sonique, Musicmatch and others.” A very nice resource!
The relative rankings in this table indicate the difference, in degrees Centigrade, among the CPU cooling options tested. For example, at 100 watts, the difference between Swiftech’s MCX462 and the Millennium Glaciator is three degrees C; at 50 watts, 1 ½ C, and so on. Closely ranked heatsinks may, in fact, show little or no difference, or even reverse positions, when compared in a specific system and especially at heat loadings of 50 watts or less.
Viewing results as +/- 5% is more indicative of what a user may find than relying on the absolute number.
First, understand what C/Ws are telling you: The difference between a heatsink with a C/W of 0.30 and 0.35 is 5 C at 100 watts under stress. At 50 watts, it’s half that. Closely ranked heatsinks may show little or no difference on a motherboard, due to secondary heatpath effects which are not captured in these rankings.
Second, I get emails from some readers who buy heatsinks and find performance does not match what they read in our and other reviews. The first question I ask is “What is the temp inside your case??” Invariably the answer is something like “30/35/40 C” – sometimes higher!
The air temp going INTO the heatsink or radiator fan is the floor – all other temps you see are added onto this temp. If the air temp is 35 or 40C going into the fan, then there is NO WAY this heatsink will give you 40C at the CPU. The following table lays out what to expect for a 100 watt CPU:
|Case Temp / C/W|
As the table shows, the higher your case temp (and fan inlet temp), the hotter the CPU temp. It’s no wonder that many are finding fresh air ducts to be a very effective solution at lowering CPU temps. Effective CPU cooling requires BOTH a good heatsink and airflow through the case.
Note that AMD’s guideline max temp for CPUs is about 70 C! (Go HERE for details)
To test out how much case temp impacts your system, open the side of the case, aim a house fan at the motherboard and record temps under stress. This is “best case” for airflow through the case.
To calculate what to expect for other CPUs, for every watt the CPU radiates, the heatsink will cool the core by the (C/W x watts) plus ambient temp. For example, at a fan inlet temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C.
Last, remember that in-socket thermistors are not accurate measures of CPU temps. Every heatsink affects an in-socket thermistor differently, as does airflow over the motherboard. There is no consistency between motherboards as well. At a minimum, you can factor +/- 5 C to these temps.
For an overview of what AMD recommends, see
AMD CPUs: How Hot Is Too Hot?
¹Heatsinks tested prior to September 2001 were newly tested during December 2001 on the Die Simulator. Heatsinks were tested at about 75 watts.
²In some instances, Die Simulator test results may be reported before a full test report is posted.