Ducts VS heatsink fans

joeatsalot · Post by **joeatsalot** » Thu May 19, 2005 12:46 am

The standard setup inside a case has the CPU heatsink fan just inside the case exit fan, perhaps even obstructing the airflow out of the case. The CPU heatsink often has the same air repeatedly churned through it at high speed, rather than a gentle supply of fresh air. Therefore, as I see it, the CPU is not really on the main airflow path, but on a sort of side branch.

I've read several articles on this site which mention ducts to the CPU heatsink. This seems like a logical improvement to me. The CPU is one of the greatest heat sources, so it makes sense to dump its cooling air straight out of the case. Then, the CPU heatsink is on the main airflow path, and all fans on this path work together.

But is it really worth trying out a duct setup? Are they really a step better than a standard HSF, or is it just a nice idea? I'd like to hear of any experiences you've had.

Paul D · Post by **Paul D** » Thu May 19, 2005 5:28 am

Sorry that I don't have any real experiences but... I think that getting fresh/external air directly to the CPU HS is definitely the way to go (as opposed to just making sure the CPU air is immediatley vented). Isn't this what the BTX form factor is all about? Once the air has passed over the CPU HS then it can be directed to less critical components or it can be vented immediately.

Some of the newer slimline cases that declare themselves 'Prescott ready' have a big vent in the side panel, directly over the CPU, with the HSF sucking that air directly - sometimes through a cowl/duct. I'm told that the CPU temps in these cases are much better than in a 'standard' case design.

BrianE · Post by **BrianE** » Thu May 19, 2005 11:30 am

Like Paul D, I don't have any experience, but I would say that it makes perfect sense to exhaust the CPU air out of the case separately from everything else. The two main components that make the inside of a case hottest are (typically) the video card and CPU, so if you can effectively remove one of those sources of heat, I imagine it should make cooling everything else a bit easier. Probably even more important for higher performance systems with hotter parts.

This recent thread mentioned some interesting results which would definitely be applicable to ducting: http://forums.silentpcreview.com/viewto ... ght=upside

joeatsalot · Post by **joeatsalot** » Thu May 19, 2005 2:05 pm

Ayaiyai! That thread is a bit shocking. Shows how unscientific standard case cooling is. 5 - 10 degrees lower temp is what you'd expect from buying a more expensive heatsink - but available for free just by playing with airflow.

Perhaps it's too hard for manufacturers to cooperate with aligning all the components of motherboard, PSU, case, etc. for good airflow.

I'll have to think more about this, and pluck up the courage for some airflow mods on Dad's next computer.

Bluefront · Post by **Bluefront** » Thu May 19, 2005 3:23 pm

Ever seen this duct setup? It's a drier vent part, with a 92mm fan on the case end, sucking heat off an Alpha 8942......no fan on the alpha. All the CPU heat is blasted right out.

IMHO.....this is the ultimate CPU duct. No heat is recirculated, no heat from the CPU goes into the PSU.

alglove · Post by **alglove** » Thu May 19, 2005 3:54 pm

Actually, I experimented a little bit myself a while back. I made a duct to supply the CPU with fresh air. Unfortunately, the duct itself greatly hindered the venting of hot air out the case. As a result, there was actually a net rise in the CPU temp. Even though it was receiving fresh air, the exhaust had nowhere to go, so the case temp went up, dragging the CPU temp along for the ride.

I eventually put the project on the back shelf and moved on to other things, but I came away with the lesson that both intake and exhaust must be considered.

Shriek · Post by **Shriek** » Thu May 19, 2005 7:56 pm

I know that ducting can work very well, in the right situation (see sig). It's going to depend on your heatsink, your case, and the airflow therein. The easiest way to duct a heatsink is usually to pull air up through the sink--and many don't seem to cool as well in this configuration. The Thermalright XP series and the Alpha are known to be good candidates.

The best way to know what's best in your case (heh) is to grab some cardboard and some tape and watch your temps. The "step better" you ask about is that usually the sink is ducted to the existing case exhaust, eliminating the need for one fan (i.e. noise source).