how big should passive intake be? to achieve decent negative pressure.

hello i have been searching around on the web, and cant find the right information since everyones setup is so different.

im now thinking against buying a tent, and wanting to build a box since it will be so easy.

its gonne be 3x3 and possibly 6 feet tall..not sure yet.

the fan im wanting to buy is a little over 400 cfm's, and the ducting will be 6" wide.

how big should my intake be?
ill prob rig up something for a light trap. not sure yet.

im assuming if i just used 6" ducting as an intake it wouldnt really be good enough, but im not even sure.
i just know i need good negative pressure.
thanks and sorry for being noob

You want enough negative pressure to prevent air bypassing your filter. Doesn't take a ton of super dank air to make a super dank smell.

I think 6" intake hole is probably good, but you could always make two with the option of blocking on off.

you need 2-3 times as much on the intake.

Get a 25$ inline booster fan, 6", from eBay. It comes with a 120v cord attached. It is 250 cfm and has worked perfectly for my intake. I can still feel a slight air exchange around the crack of my 4x4x7 rooms door. No smell outside and it smells like a skunk inside.

so 250cfm intake is not to high for a 440 cfm outake fan? im liking this idea


and if a stay passive is it really 2-3 times bigger? that makes me think that it would create no negative pressure. if anything positive.. but what do i know?

Yes it really should be 2-3x the size of your exhaust for a passive intake.

6" exhaust you need to use at least 2 passive intakes with the same area as your fan.


Trust us it really does still create negative pressure. I had 2x5" screened passive intakes and 1x6" passive intake.



J

The higher the cfm,the more passive intake is required, but ss1's statement is right at 2-3 times the exhaust you can still achieve negative pressure without starving your exhaust fan or collapsing the walls of a grow tent. You only need a wee bit of negative pressure to accomplish what it is going to give you, as excessive negative pressure is hard on everything, fans, tents and annoying to listen to as well.

Peace

Asmallvoice

thanks so much guys

having the same problem. 250cfm fan with only a little 4'' intake as passive. it sucks in the walls and seems like im sucking more air out of the room than is going in