Heatsink Size As A Performance Indicator

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SUMMARY: Sometimes size does matter: The cubic volume of a heatsink looks like a good predictor of cooling performance.

Andy Lemont at Millennium Thermal Solutions is developing a heatsink and he’s been kind enough to allow me to look over his shoulder while he does. We’ve been doing some joint testing on heatsinks and his testing expertise and knowledge in this area has been invaluable to me.

I seem to remember writing something up a while ago about “eyeball heatsink evaluation” although I’ll be damned if I can find it. Anyhow, the thrust of it was that you can pretty much tell how a heatsink is likely to perform based on the number of fins and resulting surface area (all other things being equal, e.g aluminum or copper heatsinks etc). Andy came up with a nifty graph that illustrates another approach:


Plotted are some popular heatsinks’ cubic volume vs performance. The graph shows a definite relationship between the two; when you think of it, it makes sense:

  • Surface area should show some relationship to size; A heatsink designer’s objective is to get the most cooling area possible into a heatsink.
  • For similarly constructed heatsinks (e.g, aluminum extrusions), the relationship should be even tighter; barring some physics-bending, manufacturing processes and CPU specs form a pretty tight design envelope.
  • Adjusting for fan size (as this analysis does) puts designs on a level playing field. All things being equal, we have showed time and again that higher air flow translates into better performance, but only up to a point.

So if you’re looking at a heatsink, give it the eyeball test before plunking down the cash; ask yourself:

  • How big is this heatsink compared to other?
  • How powerful is the fan and how many cfms?
  • What material is it made from (copper vs aluminum)?

These are purchasing guidelines only; there’s no substitute for critical testing. At a minimum, check out the manufacturer’s website and use their published C/Ws as an additional guideline.

Thanks again to Andy at Millennium Thermal Solutions for the analysis.

Email Joe

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