What's the difference between Vent Fan and Circulation Fan


Hello everyone, I’m a little not clear about the use of this two fan…

thx for your answering! :slight_smile:


The vent fan forces outside air into the grow chamber. The vent fan would typically be turned on and off based upon the consideration that when the vent fan is on then the outside air’s temperature, humidity, and co2 level will change the grow chamber’s values for these variables.

The circulation fan recirculates air within the grow chamber. The circulation fan would typically be set to run all the time in order to keep dead air pockets from accumulating near the plants.


Oh,got it, thank you so much!


Hi all, i have a question on fans as I’m ready to put fans on/in my “food cube”. I haven’t kept up with updates from version 1 to 2 to 2.1, etc, so i don’t know if fan design has changed from the above picture / post.

Question 1: is there only one vent fan for outside air to inside air? I would think two would be better (an outflow fan and an inflow fan).

Question 2: is there a standardised air flow regulator that is being used. My DIY self was just going to cut some rubber belt strips that would hang down to help prevent cold air flow from outside (when not wanted) and vice versa. But i also see things like “backflow vents” online and the term “louvre” being thrown around. I don’t know that term, but i get the basic idea.

Question 3 (not fan related): has the humidifier thing been ironed out or is it still hacker-ish?


@BioLumo Since this is a 2 year old thread about the ventilation design for the PFC v1.0 hardware, and it sounds like you’re interested in how to design ventilation and circulation systems generally, it might be worth making a new topic to ask about that.

According to comments from juhnke and webb.peter in this thread (Choosing Between PFCv2.1 and MVP), juhnke may be one of the few people to have a PFC v1.0 up and running this year. I think he’s using custom software that he adapted from the PFC v2.0 software stack. There’s another old post here (Chilling on the PFC1) where juhnke talks about ventilation and cooling issues with the PFC v1.0 design. All of that depends on old software that you probably would have a very difficult time attempting to install and get running now, so it might be very difficult to study the old design.

As I recall from reading different comments here on the forum, reading Rob’s PFC v2.1 test crop notes on the wiki, etc., the ventilation and air circulation on the PFC 1 & 2 designs haven’t worked well. If you want a model to copy, it might be better to look at systems where more people have reported successful grows. For example, the MVP design or perhaps grow tents.


Thanks for the reply. No i don’t see the need to start a new thread unless the OP objects. I find it easier to daisy chain onto a topic that is already the closest to what I’m looking for already. Plus it included a picture of a ventilation diagram, although i did suspect it was an old depreciated version.

I guess i can dig into the V 2.X hardware CAD etc., but i hadn’t heard that the ventilation systems were not ruining smoothly at all. If that’s the case then I’ll just make it up as i go, I’ve already got a basic idea in my head.

I’ll check out your links, but otherwise i figure someone who knows will post a reply (hopefully with pictures) of a working ventilation design.


That’s probably your best option.

@Webb.Peter, any thoughts on how to hook up a good vent fan? How do you feel about the effectiveness of ventilation in the original MVP design?


You probably would have seen it anyway, but i just wanted to update you that i have solved my problem. I have built my vent fan idea 90% of what i had in my head. I think it came out quite well. You can see it in my custom t-slot thread.