Inline fan

[Rigga Mortis]

Hi. I'm going to be using a inline fan for this grow.

My question is how do you judge the inline/extraction fans levels. Are there any special techniques or is all about judging it for yourself.

I'm using a grow tent if that helps and any advice would be welcome.


Shoot it,man! Shoot it in the head!

 

[qupee]

Fans are all rated by CFM (cubit feet per minute - or metric if not in the US).

You will want to base your fan on the size of your room - so you need to calculate the room's volume. For example, if my room is 10x10 and has 7' ceilings I take 10*10*7 = 700 cubic feet.

A good starting point for a fan is to pick CFM that's 1.5x-2x your room size. So for my example maybe 1000cfm

Now, that CFM rating is a maximum amount for the fan. Once it is hooked up and has resistance from ducting and filters that will drop. It isn't always easy to know how much it drops, but I would say take off 25%-33% for a filter and 10%-20% for 90* bends.

I would say we're aiming for one full exchange of air every minute after accounting for the drop in CFM. But every situation is different. If the air around your room is cooler, you might need less fan. Bigger rooms also need less fans, but if you're stuffing lots of lights (> 75w/sq ft) you might need more fan.

Also, a bigger fan will always be quieter than a smaller fan moving the same amount of air. For this reason I always get a bigger fan than I need and a speed controller to dial it down to where I want. And the last thing I'll say is too much air movement can be bad for plants, it can lower the humidity too much and more or less dry out the plants (someone smarter than me can explain vapor pressure differential etc.)