# Viability in reversing CPU heatsink airflow?



## Viking6 (Apr 11, 2005)

I just got an ANTEC Sonata II case. It has an air duct bringing air from outside of case to CPU area. Has anybody tried reversing the air flow so it draws air from around CPU up through the heatsink, and blow it directly outside of case, thus completely removing the heat from the case to external area? Would this work better or worse from current accepted practices? Thank you for any comments.


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## oldmn (Oct 16, 2005)

Pulling warm air from inside the case through the heat sink is not as efficient as pulling cooler air from outside and pushing it through the heat sink.


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## GarnetCompy (Feb 15, 2005)

Though your idea is plausible, I doubt it'll work. You see, the whole point of the chassis air ducting is to bring colder air to the processer cooler. Obviously, your going to get more cooling if your blowing with cold air than hot air. 

Also, keep in mind that you already have a large fan pulling the ho air out, its probably enough to exaust it.

Good idea though, if you had more air being pulled in than blown out, I think it'd work well.


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## Stu_computer (Jul 7, 2005)

blowing down into the heatsink forces air across the heatsink surface area causing maximum heat exchange.

pulling air up through a heatsink draws airflow from the edges of the heatsink and there is no forced air flow across the surface area, resulting in minimal heat exchange.


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## batty_professor (Jul 29, 2004)

Viking6 said:


> I just got an ANTEC Sonata II case. It has an air duct bringing air from outside of case to CPU area. Has anybody tried reversing the air flow so it draws air from around CPU up through the heatsink, and blow it directly outside of case, thus completely removing the heat from the case to external area? Would this work better or worse from current accepted practices? Thank you for any comments.


Air at a given temperature has the same cooling effect on a heatsink, regardless of the direction of flow, so long as it flows over the fins effectively. Of course the air inside the box will be a little warmer than the ambient outside air, and therefore will not cool quite as effectively, but only for the reason that it is warmer to start with. The fins on the heatsink comprise the majority of the surface area, and surface area is where the heat is dissipated. Someone said something about blowing air over the tiny areas between the fins being more efficient. That is not true, for if it was, there would be no need for the fins. I would stick with the current cooling scheme, and maybe add another case fan to help exhaust warm air from the box. Keep in mind, that increased airflow = increased dirt introduced into the box. I try to clean my units every 6 months or so. And I don't have extra fans in this old stuff I run. Keeping clean increases longevity by keeping cooling efficient, and dust and dirt can be conductive, causing problems of it's own.


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## crazijoe (Oct 19, 2004)

Viking6 said:


> Has anybody tried reversing the air flow so it draws air from around CPU up through the heatsink, and blow it directly outside of case, thus completely removing the heat from the case to external area?


Actually a number of companies use this paractice. The Dell Dimension 2350, for example uses a standard finned heatsink, with no fan, and has ducting over the heatsink, to the rear case fan, to exhaust the heat. I have seen 1U and 2U servers use this same setup. Even the old Alpha P2 and P3 "furnace" heatsinks used to pull air though the fins and out the fan. (shown below) The key is proper air flow throw the case. 
In your situation, it is better to cool the CPU with the cool air, from outside the case, than from the warm air inside the case. Some of the newer setups are taking this approach. Known as the BTX format. (shown below) The CPU is positioned toward the front of the case where the fresh air intake is. 
























BTX Design


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## rmarlisz (Nov 19, 2005)

i did somthing like that on my aspire x navigator. my cpu was at like 44c+. switched 120mm fan around that was blowing out, facing in. didnt make ne sense 2 me becaus that fan is rite above the mobo and everything. lol


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## please (Mar 2, 2005)

There are cetain cases(pun intended) where a fan blowing away from the heatsink will work and it usually includes some sort of shroud or duct that seals the HSF unit to force the full CFM airflow of the fan thru the HS like the above example. 

Whether it is more efficient than blowing down on or if there are other benefits as described in the examples above hasn't been clearly determined as 'better' or 'worse', but it appears to be at least a viable option when the entire case cooling needs are taken into consideration. I have read where there is a 20% gain in cooling efficiency being blown onto as opposed to being blown away from. Can't find the link right now. But that also may not take a 'whole case cooling solution' into consideration

I prefer the analogy of: on a hot summer day, do you stand in front of the fan or behind it? :wink:


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