Indoor how much larger should the exhaust vent be when there is a screen over the intake vent????

[infamousralphster]

Hi afn!,
I was wondering if anyone could help me out with a dilemna im having. I am currently helping a friend build a grow box right now and we are not sure what size intake vent to use. we plan on using a 4 inch exhaust fan / filter combo. from what i have read in order to create good negative pressure the intake hole must be half the size of the extake. so approximately a 2inch intake hole. The problem is we want to put a screen over the intake to keep unwanted bugs out but we are not sure how this will affect the air movement. i was thinking that a four inch intake with a screen might work but again i am unsure. if anybody has any clues to how much air movement is lost when using a screen we would definelty appreciate it.
thanks everybody
-Infamous

 

[roadsidevendor1]

have you considered several small
holes along the sides on the bottom.
this would allow uniform airflow.

 

[Truu]

Whats up bud. First of all the dimensions of your grow box would help out a little bit. If you are going to go with a passive intake I would drill a couple of nice size holes on each side of the box. If you are going to put some kind of mesh over the holes (im guessing) it really shouldnt effect the suction to much. If you are going to have negative pressure you might as well start off with the desired holes you and do a test run. If the fan seems to be bogging down I would make the holes bigger, and so forth.