I am currently renavating an old cupboard I used to use and giving it to a mate. It's a very small so I have limited space. The problem I had when running it was that the pc fan I was using hasn't really got enough power to extract hot air when its running through a filter. I don't really want to cut another hole into the back to add another fan as this would also men adding another filter. So my question is this. If I stack 2 pc fans on top of one another will this give me twice the extraction speed or doesn't it work like this? Any help/info would be a godsend. Thanks.
2pc fans stacked on top of each other will increase the static pressure - hence be able to push through the filter better. But the extraction speed will not be more than they can both rotate i.e. two 50 cfm fans stacked on top of each other will always push 50 cfm Research the difference between cfm and static pressure; it is static pressure that matters most when pushing through a filter - although achieving cfm is the goal. Personally I couldnt get PC fans to work with a CF and had to resort to proper fan/cf combo with a fan speed controller.
Thanks for that. It is the static presure that I need to build up as it is quite sufficient without the filter on. I will try doubling up the fans and see how I go with that. If that fails then it will have to be a 4" inline fan and filter allthough personally I think it's a bit overkill for a microgrow. It would probably be ok if I ran it through a dimmer to reduce the speed though.
That exactly what I had to do, although a dimmer will make the fan whine a lot.. you should build a speed controller with a variable transformer. My grow journal may help here as it describes the problems I had with the PC fans http://forum.grasscity.com/micro-grows/1112072-northern-lights-autoflower-micro-grow-journal.html Good luck and post some pics