Why is it better to have a rear fan than a front fan?

[Denis54]

Most good cases, like the Antec 3000B, have a rear fan while most cheap cases have a front fan.

Why is it better to have a rear than a front fan?

 

[Tu13erhead]

Rear fan is closer to heat critical components, i.e CPU, GPU, RAM, etc.

 

[RallyMaster]

It is to exhaust the hot air. If you have an intake, you'll be providing cold air, but the hot air is less likely to get out.

 

[Dumac]

I would *think it would be* be better to have both..Intake on bottom front and Exhaust on top back

EDIT: added the words in astrics

 

[Zepper]

If you can have only one additional fan (besides what's in the PSU), then an exhaust fan is the better choice, partially for the reason RM mentioned. When a case has only one fan as standard equipment, it has been my experience that it is mounted as an exhaust. I would seal off any large areas of vents or other air holes in the case other than whatever is near the bottom front, so that any air that is pulled into the case by the rear exhaust fans (PSU + additional) takes the longest possible path thru the case picking up more heat along the way. Because air, water, electricity and students all take the path of least resistance...

Some case makers may think that the fan in the PSU can act as the exhaust for the system too, but most modern PSUs have a thermally-controlled fan(s) which is ineffective as the sole exhaust fan in a system. I've often found that I either have to bypass the thermal control in the PSUs or bring the fan wires out to a manual fan controller as it is ineffective at even cooling the PSU adequately (the exhaust air is too warm for my comfort zone). As the 80mm fan in my Zippy was too loud (it's a server PSU so the fan was set up to be full-speed 24/7), I took it out, cut out the fan grill (very obstructive) and mounted a 92mm fan to the outside of the PSU case with an adapter. Now that COULD cool the case and the PSU if I wanted to do it that way ...

Right now (and as you probably know) the sweet spot for noise and cooling balance is 120mm fans front and rear.

.bh.

 

[Mrvile]

Exhaust is the most important thing in air cooling, so a good rear exhaust fan is a must.

 

[imported_Kiwi]

Originally posted by: Denis54

Why is it better to have a rear than a front fan?

Like almost anything else involving PC component choices, the terms "best" and "better" are terrible criteria to attempt to use, because of personal subjectivity and differences in the box's designs, so "it depends" is where we end up. One of the most seriously considered reasons for fewer front fans being pre-mounted is simply the noise factor. But when various reasonably good case designs are taken into a lab for actual measurements, and a single fan is all that is used, other than the one in the PSU, many recently produced boxes with 120 mm front fan mounts begin showing excellent overall heat reduction results.

I'd love to offer a LINK for you, but I ran across this in a review of enclosures, very possibly right here at AT. (No, I don't think that's accurate, after all.) Wherever the site is, it is one on which different cases are compared, and a grid of heat zones are compared on numbered diagrams. As I recall, for enthusiasts with strong interests in Overclocking, the HSF's are getting better assistance from rear panel exhaust fans than from either front or side panel intake fans. However, once you already have a first fan as an exhaust, then a choice of front or side for intake may have to be made based on which of the two has the better intake flow path (few front intake mounts in low price cases are well designed, so the only intake is often a narrow lip slot at the bottom of the front bezel/ facia).

One of the most interesting results I have seen relatively recently is exactly how little value is obtained from an 80 mm fan in a top panel blow hole. I would think just from ordinary physics that rising air would already be collecting up near the top panel, in front of the PSU, but seemingly there isn't that much getting that far in most cases.

Geting back to my initial observation about subjectivity, in an environment where noise is critical to the results, such as a fan being used in an HTPC, the front fans are much harder for the enclosures to muffle sound from. My own personal choices, when limited to 80 mm mounts in oridinary enclosures, have been a single exhaust, whether or not twin mounts are offered, and a single side intake, located slightly closer to the VGA card than to the CPU, but in line with the CPU vertically (and this is a popular spot already pre-chosen on many of the windowed boxes).

 

[0roo0roo]

front fan generally doesn't have the best venting..theres the bezel and whatever else in the way. doesn't help with noise either with air rushing over all this clutter..and it leaking right out straight at the user. better to use rear case fans.