Are intake fans necessary?

[antef]

I have a Silverstone PS07 that comes with two front intake fans. I also added an exhaust fan because it just seems reasonable to forcibly exhaust some of the warm air out the back. I was playing around with SpeedFan and lowered the front fans to 0 and saw no increase in CPU temp - in fact, CPU temp started going down a degree or two. When the fans are set back to 500-600 RPM, CPU temps go up a degree or two. Why might this be? How could the intake actually hurt temps slightly? Are these fans necessary at all? My hard drive is mounted up top so it doesn't benefit from them. I imagine the air might do some good for the SSD, motherboard, and video card, but the video card also has its own pretty beefy cooling. I'm wondering if these fans are worth having.

Regarding the exhaust, using something like the Hyper 212 would allow me to have just one fan that acts as the CPU fan and exhaust at the same time. If I did that and removed the front fans I'd be down to just 1 120mm for the CPU/exhaust, the GPU fans, and the PSU fan, no case-mounted fans at all. Could this be a good way to go?

 

[tracerbullet]

Random thoughts:

* A degree or two is probably within the margin of error of whatever your test was, which means you could also say there really was no change, as opposed to there being a bad one
* Your layout could be such that front fans disrupt airflow in such a way that they swirl around more hot air than they introduce cold air
* You might not be creating enough heat during your normal usage to benefit from extra fans, and ditching them might be fine
* All that matters is that you cool the important parts sufficiently, if you don't need front fans to do that then... you don't need them.

 

[gandhi1]

First I'd recommend using a tool like Hardware Moniter so that you can track the SSD and GPU temps all in one place, just to make sure they are doing ok.

If you do get rid of the intake fans I'd still recommend keeping the outtake fan. Just do a stress test like Prime 95, then put your hand back and feel the air coming out. It will probably be pretty warm. All that heat will stay trapped in the case without it.

Of course you can experiment with it off and see how things work out.

 

[MadScientist]

Interesting article. Fast forward to the Summary and Conclusion page.
http://www.bit-tech.net/hardware/2012/02/10/the-big-cooling-investigation/1

 

[lsv]

I will always use more intake fans than exhaust. The intake fans should have dust filters as well. You lost airflow with the filters but if you use extra fans you can make up for the lack of air and less dust means less maintenance and same temps for quite a good while.

 

[Ketchup]

I use intake to cool the hard drive, not the CPU. Without intake fans, the CPU will get intake air from anywhere it can find it. With front fans, you are directing air, and thus cooling what needs to be cooled, not just the CPU. It makes sense to me to use a fan to cool the part of the computer that is spinning at 7200 RPM.

 

[antef]

Interesting article. Fast forward to the Summary and Conclusion page.
http://www.bit-tech.net/hardware/2012/02/10/the-big-cooling-investigation/1

It looks like that link emphasizes exhaust more than intake. But people seem to prefer intake over exhaust due to positive pressure. It seems I could eliminate all 3 case fans and temps wouldn't budge much at idle, but I'd have to watch all the temps under load. Overall I feel more comfortable keeping airflow going when it's under load, but I was wondering what people's experiences were with the effectiveness of intake fans in general.

I'm fairly satisfied with the noise level generated by 3 low RPM 120mm case fans. However when I set the fan level to something < 5 on my motherboard sometimes they don't turn on at all. That's too bad because anything higher puts them at 600+ RPM which I'd rather stay below. Anyone know why they might not turn on at 400-500 RPM?

 

[tracerbullet]

Maybe not enough juice to get them turning to begin with. Seems that most fan speed controllers start high and then ramp down, to make sure things get started then nestle back to a steady state. Strange that your mobo doesn't do that, but that could still be the case.

I like intake fans > exhaust fans, simply because I know where air is going in, can filter it, and occasionally vacuum those filters. Keeps the case and everything else clean. Seems to be working well, because prior to that (without thinking about it, just sort ended up this way) I had mostly exhaust, and it seemed like flash card readers, CD drives, and so on were always dying. In retrospect that wasn't a big surprise since I did notice they were always dusty. It's embarrassing it took me so long to finally put an end to that.

 

[Vectronic]

However when I set the fan level to something < 5 on my motherboard sometimes they don't turn on at all. That's too bad because anything higher puts them at 600+ RPM which I'd rather stay below. Anyone know why they might not turn on at 400-500 RPM?

Not to be rude, but unless the fans are rated for sub-500RPM or <5v... that's why.

Assuming it's not the most basic of basic fans (2 wire, direct to coils in the fan) you could try popping them apart (can be almost if not impossible with some fans) and seeing what's under it's hood... more advanced fans will have their own electronics for temperature, speed, power going to the coils, etc.

The fans might run at 250RPM, or 3v or whatever, but it's not allowed to, the fan itself is shutting down because it's electronically designed to only run once it has a certain amount of power (to prevent stalling and burning out a coil, plus a bit to compensate for error tolerances in manufacturing, etc)

Skip the motherboard, rig up some highly technical device to test this, like shoving two 1 inch long wires into the fans connector... connect it to a couple AA batteries... if it spins, then it's the motherboard.

Regarding the topic, yes exhaust only is better than exhaust + intake... try it in your house in the summer... one fan pushing air out will cool your house far quicker than 3 fans sucking air in.

But, like mentioned, positive (sucking in) pressure is better for keeping dust out (if you have filters).

 

[antef]

I'm not sure exactly what the fans are rated for, but it does seem like they can run at pretty low speeds, just not necessarily start at those very low speeds like tracerbullet said. Either way, I have found that I'm happy with ~500 RPM - at that speed they seem to usually start up with the computer, and even if one doesn't, it will later if load increases. I think I can agree that exhaust seems to make more sense for cooling but filtered intake helps with dust. Given that, one exhaust and at least one intake (I have two currently) seems fine.

Thanks for all the input.