Push or Pull?

  Stowit 17:08 03 May 2004

I'll shortly fit a case fan to my PC as since fitting a Zalman Heatsink it's getting warm. I've 2 spaces, but 1 fan at planned at present. Am I better exhausting warm air or sucking in cool?

  QuickHare 17:14 03 May 2004

You really need to do both. Air pushed in has to go somewhere, and back out the fan it came in usually is the only way (unless you have other vents). Air sucked out has to come from somewhere, so air will have to go in at some point.

If you have two fans (one in, one out), then it creates an air corridor, which moves the air in one direction only, making the two fans more effecient at their jobs.

If you can only put one fan in, though, I don't know which is better. It depends on what type of case (Midi Tower, Maxi Tower, Desktop, Laptop, etc) it is and what obstructions you have inside (an AGP card right next to the air intake, for example).

  Ladaman 17:15 03 May 2004

Hot air out in my opinion (although its through intuition not experience)

Drawing hot air out will automatically bring in cool air.

Blowing cool air won't neccessarily help the CPU, depending on how the air flows around the inside of the case.

  Mikè 17:17 03 May 2004

Exhausting, high up at back is best.

  Stuartli 17:22 03 May 2004

The front case should pull air in (the direction of the air flow is usually marked on the fan itself) and this in turn will be pushed out by the PSU's fan.

But make sure that there is the best possible air flow through the case by moving/tying IDE and other cables as much as possible out of the way.

  Stuartli 17:25 03 May 2004

It's impossible for a fan to both input/output air unless you could change the fan's direction of rotation each time...:-)

That's why the air flow direction is usually marked on the case with an arrow or similar mark.

  Stowit 17:50 03 May 2004

My 'fan spaces' are 1 at the front with concealed intakes, 1 at back, with lots of vent holes (also PSU is at back with its' fan). I'll probably get another fan, but I'll see how I go on, with one on exhaust to start with. In trying to reduce noise it looks like I'll be inundated in fans! Also, all the fan controlers to reduce the racket, & may yet end up with even more!! (2 on CPU, & in & exhaust + PSU). Now what about water cooling ???????

  QuickHare 18:41 03 May 2004

The bidirectional fan thing was my point. It's impossible to make it in in AND out, but the air has to go somewhere. The most likely way is throguh the fan, which is against the air flow, and hence drops performance of the fan. Ergo, it is less efficient than having two dedicated air intake and air outtake fans (one in, one out).

  Stuartli 09:28 04 May 2004

Even if you only have one main fan (perhaps that at the rear) plus CPU/graphics card etc there will still be air being "pulled" through the case from air inlets at the front (front case fan slots or holes); obviously it would not be as much as if it was aided by a front fan.

I only have a front case fan and the PSU fan (plus CPU and graphics card fans), but these are more than sufficient in my case, though not necessarily for more powerful systems.

  Gongoozler 10:15 04 May 2004

The important thing is for the air to flow over the motherboard. It is normal for the air to be taken in at the front of the case simply because warm air coming out of the case front on a hot summer day (remember them?) would be uncomfortable for the user. The power supply blows air out of the back of the case, so additional fans should reinforce the flow in that direction. A fan blade is designed to work only in one direction, the blade is curved so that it scoops the air up slowly and then accelerates it towards the back edge. The same fan can, of course be fitted either way round so that it can suck or blow. A secondary advantage of having fans at the back ofthe case is because it is quieter that way.

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