Hi
Sorry if this is a stupid question but i can't seem to find anything anywhere about this. I have an extra 12 cm case fan sitting around and i don't want it to go to waste so i was thinking about screwing it into another fan. I think that it would do the same thing as with one fan (45 cfm fan running with another 45 cfm fan running behind it). Any kind of answer would be appreciated. Like i said i don't want it to go to waste but i don't want it in my case doing "nothing".

It'll move somewhat more air, but definately not twice 45cfm (90cfm). Make sure both fans are identical and spin at the same rpm, or they may produce a lot of noise. The gain probably won't be very significant. People don't do it because it's not worth the trouble.

yeh id tend to agree, different RPM's could also start to create a bit of a vacuum between the 2 which would lower any gain significantly.

I wouldnt even bother, have you considered mounting it elsewhere?

I agree with Dagger, also if 2 case fans are mounted next together and are no identical problems would be more than gain. A bit vacuum between 2 fans and also noisy.

Get out the Dremel! (/drill/jigsaw)

Angle grinder

Not worth it. Fans are designed for an ideal situation of not having anything restricting the inlet and outlet. As soon as you put anything next to them you get less CFM and more noise, so you'll get a small CFM increase for a big noise increase (and power consumption goes up too, as both fans have to work harder).

There are piggy backed redundant fans in servers, but they are specially designed to reduce turbulence, to keep CFM up.

ok thank you very much for all your guys' help i think since they are the exact same fans i will try to put them together, if it helps at all at least i won't be wasting the fan

If you must put them together...
consider adding some space between the 2 1" should suffice...
cardboard and some duct tape will do the job nicly...
this will eliminate some of the noise

There is a graph here on multiple fan use that's pretty interesting, it's about 1/5 of the way down the page: http://www.nmbtech.com/html/fans/e [...] g_101.html

^ Yes, that reference gives a pretty good relationship. In other words, it increases the pressure but not the flow (volume). You will see some increase in velocity but not double due to losses. In fact, since these are very inefficient fans, I'd be surprised to see better than 40 or 50% increase in velocity or static pressure. I think it's hilarious to see these computer case fans rated at 45 cfm!

Panaflo H1A 12cm fans FTW...

104 CFM @ 42 dBA

Like a jet taking off... but it sure moves some major air!

Back in the day i had a case with 3 of these babies... I've grown out of that phase, though