How important is it to equalize fan intake/exhaust?

3

How important is it to make sure that my intake and exhaust fans are moving equal amounts of air?

I have seen various answers to this online, ranging from that it is unimportant, to it could strain the fans if the intake is significantly more or less than the exhaust. I even had one person tell me that it could damage (i.e. implode/explode) the case if they are off balance.

Intuitively I would think you would want slightly higher intake than exhaust to make sure as much of the air as possible is coming through the filtered intakes and thus minimize dust.

So how balanced should I try to make my intake/exhaust airflow? It seems that it is a fairly difficult thing to do (even if you can find the CFM of all your fans) since they don't always run at top speed and things like my cooling radiator could affect it as well.

PGmath

Posted 2016-04-02T22:19:29.850

Reputation: 1 430

My experience says you are trying too hard. your intake won't pump more air into the case than the exhaust can displace. we are not talking about forces sufficient to increase pressure in the case much beyond standard atmospheric pressure at your location. Either way, any modern motherboard will automatically adjust fan power based on runtime conditions, and unless you have a very sophisticated board, you cannot control those reactions. Even if you could, you can only operate thermal sensors, not power output to given fans, so it would be quite difficult to define a profile for each fan. – Frank Thomas – 2016-04-02T22:41:06.580

2PCs have historically (since the original IBM PC) had negative pressure in the case, i.e. the single fan in the PSU blew air out (and pulled unfiltered air in). Whereas industrial electronic equipment typically have a filtered fan blowing air in, i.e. positive air pressure. But in neither situation is there balanced flow. Instead of balanced flow the far more important (and difficult) goal is to achieve good circulation within the case so that there are no/few dead zones that can become hot spots. – sawdust – 2016-04-02T23:04:22.293

Answers

3

Lets start with this while we are still close to April 1st:

I even had one person tell me that it could damage (i.e. implode/explode) the case if they are off balance.

Hahahahhaha! That was a good joke from that person! :)


Now to a more serious answer:

Intuitively I would think you would want slightly higher intake than exhaust to make sure as much of the air as possible is coming through the filtered intakes and thus minimize dust.

I agree. If you have filters then try to drag the air in though those filters. Either by:

  • Sucking air in near those filters
  • Blowing air out elsewhere in a reasonably closed case causing most of the air to be pulled in via those filters.
  • Or doing both.

You seem to be doing the last. That is a good setup, but do not worry about perfectly balancing flows. That is both hard to do and not needed. Just make sure that the cool air flows where it is needed. Do not worry to much about the rest.

Hennes

Posted 2016-04-02T22:19:29.850

Reputation: 60 739

That was my mental reaction too when I heard the guy at the computer store say that, but he seemed fairly knowledgeable about everything else so I just took it with a grain of salt. – PGmath – 2016-04-02T23:25:47.950

Asked: 2016-04-02T22:19:29.850

Viewed: 833 times

Active: 2016-04-02T23:05:23.157