Which direction should the heatsink fan blow?

[salz]

Should the fan on my heatsink blow into the processor or pull air away from the processor? I installed a Thermalright AX-7 and I'm using a manually adjustable Enermax 80mm fan (I think I can adjust the fan between 1000-3000RPM through rotating switch). I read that it can go from 10-46 CFM, so 46 CFM should be plenty to keep the processor cool. It's can AMD Athlon 1800+ running at normal clock speed and my temperature (according to the BIOS on my Giga-byte 7VRXP) is between 45-48 degrees celsius when there is no load on the processor. I'm not upset with these temperatures, but I was getting around these same temperatures with the stock heatsink and fan that came with the processor (I don't remember exactly, but I think the old temps were 46-50 without a load). I was expecting a much lower temperature, maybe something around 40. I also use Arctic Silver III. Shouldn't these temps be lower? And should I flip my fan around and see what that does?

 

[John]

AX-7 = fan should BLOW on to the heatsink. However, try it both way and see how it works for you.

 

[PerfectFit]

Sorry John, but you got it backwards! The heat sink draws heat away from the CPU, and the fan sucks the heat away from the heat sink to cool it - it shouldn't blow on it, that's not as efficient thermally.

 

[bozo1]

According to their website, the AX-7 is designed to blow air down onto the heatsink/processor. I've tried mine both ways and that's the coolest, at least in my rig.

 

[John]

Originally posted by: PerfectFit
Sorry John, but you got it backwards! The heat sink draws heat away from the CPU, and the fan sucks the heat away from the heat sink to cool it - it shouldn't blow on it, that's not as efficient thermally.

No, not all heatsinks need the fan to suck air away. Depending on the heatsink designs, the fan needs to blow/suck in a given direction. However, as I also stated YMMV so try it both ways. This topic has been discussed at great lengths over the years.

Should the AX-7 fan blow in or out?
Blow or suck?
Blow on the cpu or away?

 

[HalfCrazy]

Try installing a few case fans in the system if you don't have some all ready. That should help to get some air flow moving. I run a XP1700+ w/ a AOpen AK73 Pro(A) mobo. I'm using a GoldOrb3 HSF on the processor and have 5 case fans. I never seen my system go over 40c under heavy load yet. But of course we do keep our house very cool in the summer.

 

[Amused]

I do know that all retail P4 Intel fans blow. As does my Thermaltake P4 HSF. As did the Retail PIII/PII fans as well. So, in every application I've worked with, they all blew.

 

[Woody40]

John's got it right. Best way to find out is run cpu at load, close chassis, and adjust your fan to blow across heat sink fins and pull across heat sink fins. Use configuration that gives lowest temps.

 

[Tweakin]

If the heatsink has closely spaced fins, then the fan should bow air through the sink...if the fins are spaced further apart, then the fan should pull air through the sink....

 

[Boobers]

Think about the convection heat transfer this way:

When the fan blows on the heat sink, it pressurizes the area between the fins, causing turbulent flow which effectively "scrubs" more heat from the entire surface area of the fins than if the fan were sucking. When the fan sucks, it creates a slight vacuum at the top of the fins and the only pressure to fill the vacuum is atmospheric pressure. This flow is more linear and may not cool every part of the fin. YMMV...

 

[salz]

I've tried the fan both ways and it didn't make much of a difference either way, except that it was louder when the fan was blowing on the heatsink. I then thought maybe my case temps. were too high and connected my fans to a main power cable and not the "fan only" cable, which I think gives more power to the fans and makes them spin faster. The system was definitely louder, and a little cooler, but not enough to make it worth the extra noise. I have a Lian-Li PC-65 case, two intakes, one exhaust on the back and an exhaust on the top. Through all of this my cpu temps. have ranged from 45-48 without going above 48 (without a load). I don't know, maybe my computer just really likes that temperature

. Not that these temps are bad, but I was hoping for something better than this with a new AX-7 and 80mm fan.

 

[Tanked]

I've also tried both directions, but the temperature difference for me was absolutely nothing (which surprised me). Right now I have it sucking air across the heatsink, but my situation might be different because I have one of those 80mm-to-60mm "funnel" adapters to reduce the noise.

 

[snow patrol]

Generally, I've found that when the fan is sucking air ONTO the heatsink, temps are a couple of degrees C cooler. However, I've also found that this way requires you to clean and unclog the heatsink a bit more often, as it can tend to get dusty. Of course this is dependant on what type of heatsink you have.

 

[hopeless879]

My temps are lower with the fan blowing towards the heatsink. About a 2º difference.