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Need experienced advice on passive/forced intake

coooper

Active member
Honestly I thought I had this figured out, but now I have confused myself so much i dont even know what to ask, so bear with me. My room is about 10x8x8. I will be using an 8 inch hyper fan for my exhaust vented out a basement window. So, my question is passive or forced intake? And the complicated part for me is, if passive, how do i maintain negative pressure and no light leaks when my exhaust is not running? I am leaning towards forced, but then it confuses me on the technical side of things being how much air im putting out vs pulling in. I have two spare 4 inch can fans that i can use for two forced intakes. And say if thats what i go with, two 4 inch forced intakes, how do i setup so that when my exhaust is on, my intakes are on and vice versa. Sorry if the question is all over the place, my mind is too!:dance013:
 

OldCoolSativa

Well-known member
Honestly I thought I had this figured out, but now I have confused myself so much i dont even know what to ask, so bear with me. My room is about 10x8x8. I will be using an 8 inch hyper fan for my exhaust vented out a basement window. So, my question is passive or forced intake? And the complicated part for me is, if passive, how do i maintain negative pressure and no light leaks when my exhaust is not running? I am leaning towards forced, but then it confuses me on the technical side of things being how much air im putting out vs pulling in. I have two spare 4 inch can fans that i can use for two forced intakes. And say if thats what i go with, two 4 inch forced intakes, how do i setup so that when my exhaust is on, my intakes are on and vice versa. Sorry if the question is all over the place, my mind is too!:dance013:

Passive intake. You reduce the number of pieces of mechanical equipment that consume energy, make noise and can fail from >1 to 1. You can't maintain negative pressure if the exhaust fan is off, regardless if your intake is active or passive. Axial fans are terrible at moving air through ductwork; and they're noisy and inefficient. Go with a squirrel cage blower on the exhaust.
 

coooper

Active member
Ok, originally that was my plan but then pressure and light leaks and stuff concerned me but i could construct an easy way to have a big passive intake through a hepa filter. Ive been constructing two rooms for a year now to host perpetual cylces, but am starting smaller with just one room for a few runs. Been so much to think about. This is in a basement with full drywalled rooms made specifically for this so im not terribly concerned on noise and have heard/read many good reviews on the hyper fans. Its the smallest 8 inch fan while maintaining high cfm. Same size as a 6 inch can fan.
 

Snook

Still Learning
Veteran
Honestly I thought I had this figured out, but now I have confused myself so much i dont even know what to ask, so bear with me. My room is about 10x8x8. I will be using an 8 inch hyper fan for my exhaust vented out a basement window. So, my question is passive or forced intake? And the complicated part for me is, if passive, how do i maintain negative pressure and no light leaks when my exhaust is not running? I am leaning towards forced, but then it confuses me on the technical side of things being how much air im putting out vs pulling in. I have two spare 4 inch can fans that i can use for two forced intakes. And say if thats what i go with, two 4 inch forced intakes, how do i setup so that when my exhaust is on, my intakes are on and vice versa. Sorry if the question is all over the place, my mind is too!:dance013:
air flow/volume exchange is confusing but why/when is your exhaust fan not on? I only turn mine off after a run for only a short time until the next vegging run is started, the 24/7.. but addressing the exhaust out the basement window does present lite leak probabilities whether the fan is on or off.. I'm a passive guy, keeping the exhaust fan running at a low enough speed to create that negative pressure and good air flow.. theres a thread Ventilation 101> https://www.icmag.com/ic/showthread.php?t=112862https://www.icmag.com/ic/showthread.php?t=112862 that is very good
 

starke

Well-known member
Read the thread Snook referred you to. Just a heads up from a comment you made in your first post, which you will see when you read the thread, with an 8" fan you will need approximately 16 square inches of intake area...not 8.

You will like the Hyperfan. They are hard to beat for the price. I run their six inch and ten inch fans. Take a look at the Phresh carbon filters as well. Considerably less than Can but I think every bit as good based on my experience.
 

Phaeton

Speed of Dark
Veteran
Personal choice for me is a forced intake and adjustable passive exhaust.

Stirring and mixing the air in the plant's canopy is crucial. A tunnel of air blowing into the room creates a vortex all around the airflow.
This movement keeps fresh air in and around the leaves, aiding cooling and respiration.

An active exhaust pulls air from the immediate surroundings, four or five inches in every direction including along the wall. Movement in the room itself is nil. Air does not actively move through the canopy, it goes around the plant instead.

Another benefit is positive pressure. A furnace filter is used before the fan, a Hepa filter will work but costs more, the furnace filter keeps out bugs and hairy dust.

Not every room has choices, after my kids grew up I had a whole house to modify any way I saw fit, so I did. What used to be my income is now my old guy hobby, output is a fourth of what it used to be.
 

Palindrome

King of Schwag
Passive intake all the way, you don't need your room to be under pressure all the time.
Unless you have draft pass your passive intake, but if you wanna filter your intake.
Try to take a look in my diary, I've made a passive carbon filtered in-take. As I some times work with paint and epoxy in my garage, and I don't want my plants to be breating that either.

Link in my sig.
 
I've had the best luck with passive intake that is double the area of the exhaust. That config keeps constant negative pressure, without adding needless head pressure to your fan. Even with active intake - exhaust should never be fully off, that's a recipe for mold, and starves the plants of air exchange.
 

Spaventa

...
Veteran
Ducted intake fan hung in grow space directed at canopy FTW - no additional noise or electric cos you can ditch air movers plus this way you are blowing the canopy with clean fresh cool intake air not just "stirring and mixing" up the used air.
Means you can run lights closer, get better penetration, higher yields.
Guaranteed negative pressure with LARGER exhaust fan. Guaranteed no invasions with filter screen on intake fans inlet.
 

coooper

Active member
Yes thanks everyone. i actually knew not to shut the exhaust off for all the reasons you all have said, think i had one too many dabs when i posted this and was confusing myself lol. As for the intake, i will be doing passive intakes using Horti Control dust shrooms. I have another thread ive posted with all the details on my rooms thus far for those interested.
 
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