Need experienced advice on passive/forced intake - Growroom Designs & Equipment - International Cannagraphic Magazine Forums

coooper · 02-27-2018, 10:22 PM

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!

OldCoolSativa · 02-27-2018, 10:31 PM

Quote:

Originally Posted by coooper

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!

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.

RanchoRelaxo · 02-27-2018, 10:41 PM

Yeah just have passive intakes. Like old cool sativa said you won't have negative pressure with the exhaust off.

coooper · 02-27-2018, 10:47 PM

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 · 03-07-2018, 01:38 PM

Quote:

Originally Posted by coooper

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!

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 · 03-07-2018, 02:28 PM

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 · 03-07-2018, 05:39 PM

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 · 03-07-2018, 05:57 PM

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.

CareStaker · 03-07-2018, 06:34 PM

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 · 03-07-2018, 08:03 PM

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.

02-27-2018, 10:22 PM	#1
coooper Newbie Join Date: Jan 2017 Posts: 20	Need experienced advice on passive/forced intake 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!
	Quote

03-07-2018, 02:28 PM	#6
starke Member Join Date: Aug 2015 Location: Between Key West and Perdido Key Posts: 669	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. __________________ “We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true.” ~Robert Wilensky "Spread the knowledge, be humble if you don't know, be helpful if you do, if you are wrong, admit it quickly and emphatically, and overgrow the world." (SuperWeed 2017) "Always keep in mind that when the hearse pulls up to pick you up, there is no trunk or luggage rack on that bitch." (Author unknown) Current Grow: https://www.icmag.com/ic/showthread....343153&page=20 Page 20 forward
	Quote 1 members found this post helpful.

03-07-2018, 05:57 PM	#8
Palindrome Member Join Date: Jan 2018 Location: Republic State of Banana Posts: 193	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. __________________ A New Start - diary of a retired farmer
	Quote

03-07-2018, 08:03 PM	#10
Spaventa ... Join Date: Oct 2006 Posts: 1,505	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. __________________ ACE New Malawi cross test grow https://www.icmag.com/ic/showthread....=1#post8189894 Delicious Critical Jack Herer ACE Panama Haze https://www.icmag.com/ic/showthread.php?t=349398
	Quote

02-27-2018, 10:41 PM	#3
RanchoRelaxo Member Join Date: Feb 2018 Posts: 61	Yeah just have passive intakes. Like old cool sativa said you won't have negative pressure with the exhaust off.
	Quote

02-27-2018, 10:47 PM	#4
coooper Newbie Join Date: Jan 2017 Posts: 20	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.
	Quote

03-07-2018, 05:39 PM	#7
Phaeton Speed of Dark Join Date: Apr 2011 Location: Interior Alaska Posts: 1,554	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.
	Quote

03-07-2018, 06:34 PM	#9
CareStaker Member Join Date: Jul 2014 Location: 42°N - Beantown Posts: 59	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.
	Quote