How big should my intake be, compared to my exhaust?

ILoveYouSweetLeaf

ILoveYouSweetLeaf

Well-Known Member
I know my ventilation intake is supposed to be bigger then my exhaust , but how much bigger?
I have heard the intake is supposed to be 2-3 times bigger then the exhaust.
and I have heard its supposed to be 4 times bigger then the exhaust minimum.
anyone know for sure?

planning my grow room and I have a 4" exhaust which gives my exhaust about 12" of surface area.
my intake I am planning to be 6", which gives my intake about 28" of surface area.
that gives my intake about 2.3x the surface area of exhaust.

is this the correct size???
 
Big Trees

Big Trees

Well-Known Member
and i believe you should be pulling 3x the amount of air that you're pushing. So if you're exhaust is rated at 600 cfm then you need an intake rated at 200 cfm or lower
 
ILoveYouSweetLeaf

ILoveYouSweetLeaf

Well-Known Member
sorry I was not clear.
I am not talking about my fan size, I am talking about the surface area of my intake and exhaust holes.
(gonna be using phresh filter rated at 200 cfm, can-fan rated at 270 cfm)
 
Dogenzengi

Dogenzengi

Well-Known Member
Hi Big Trees,
3 to 1 ratio for air sounds like a lot, I am planning just slightly over 2 to 1 exhaust to supply in CFMs
400 out, 160 in.
peace,
DZ
 
ILoveYouSweetLeaf

ILoveYouSweetLeaf

Well-Known Member
I prefer this site over others, but from what I have seen it lacks info on ventilation. found what I was looking for on icmag.com ventilation 101 post. and other posts.
 
jondamon

jondamon

Well-Known Member
Is your intake going to be using a fan?

Passive intake needs 2-3x the surface area of your fan.

Powered intake then a minimum of 10% less power than your exhaust is required to keep negative pressure.

IMO a filter should ALWAYS be rated higher than the fan being used. Otherwise air passes too quickly over the carbon bed to be scrubbed effectively.

I use a 400CFM filter with a 300CFM fan.


http://urbangardenmagazine.com/2010/07/planning-your-grow


Link to grow room design


J
 
ILoveYouSweetLeaf

ILoveYouSweetLeaf

Well-Known Member
yes its passive, stuff is ordered now. gonna be using 4" exhaust (surface area of 12 square inches) and intake 6" (surface area of 28 square inches) so intake is 2.3 times bigger then the exhaust. getting a can-fan s600 has 270 cfm and phresh filter with 200 cfm, but I got oversized fan so I could use speed controller to use the fan at 50-60 percent.
 
C

contraptionated

New Member
Always remember that if you're extractor fan craps out and the intake fan is still going , you will create a large amount of positive air pressure and the odors will leak out big time. That's why passive intake is the way to go. There is no benefit from wasting watts to push in air that is already being pulled in to begin with.
 
T

T.H.Cammo

Well-Known Member
I remember seeing a video on "UK 420" some years ago. They were seeking to answer the same question as the OP's, by actual experimentation and making a video to document the results - it was very "Professional" and very thorough I might add!

They started with a small greenhouse structure that was maybe 5 or 6 feet square by about 7 or 8 feet tall. The "room" was equiped with a "good sized" extractor fan, let's say an 8" inline fan with an 8" duct, or about 50 square inches. The room had several covered "Ports" that were also about 50 square inches each that made up the "Passive Intake Lineup". The whole idea was to set off a smoke bomb of known quantity inside the room and time the various amounts of Passive Intake (1, 2 or 3 doors, etc.). The amount of elapsed time the process took was considered to be from the time the extractor was activated until it blew "Clear Air".

The best results (quickest ventilation times) were obtained with a whopping 5 times the area of the extractor fan. 6 times the area gave almost no more improvement. The 5x area was already exhibiting some serious deminishing returns, so it may not be practical. I have always considered "4x" to be the best for a passive intake - "3x" at a minimum.
 
J

johnluke

New Member
ok well i got a 10x10 tent and am running a black dog platinum XL LED. i have a sentinel controller which controls my temp, humidity, and co2. i am using a tank to supply my co2 and am cooling the room with a portable air conditioner. i was wondering if it is still necessary to vent the room evn though all the environmental conditions are being met? i was gonna put a carbon filter and a can fan in the room outside the tent. that way my plants can soak in co2 and smell is not an issue! so once again, would i need ventilation in my tent?
 
jondamon

jondamon

Well-Known Member
johnluke said:
ok well i got a 10x10 tent and am running a black dog platinum XL LED. i have a sentinel controller which controls my temp, humidity, and co2. i am using a tank to supply my co2 and am cooling the room with a portable air conditioner. i was wondering if it is still necessary to vent the room evn though all the environmental conditions are being met? i was gonna put a carbon filter and a can fan in the room outside the tent. that way my plants can soak in co2 and smell is not an issue! so once again, would i need ventilation in my tent?
Click to expand...
If you are providing Co2 then you don't need to vent your tent.

Some folks running a sealed environment vent at night but that's mainly to control humidity.

If running a dehumidifier then you can forget about RH bring a problem.


Sealed environment generally utilise a free standing fan and filter to control odour.


J
 
J

johnluke

New Member
hell yeah man good looking out, u save me from buying a few more fans and more ventilaton. ive been looking for the answer to that Q everywhere for about a week now!!!
 
jondamon

jondamon

Well-Known Member
johnluke said:
hell yeah man good looking out, u save me from buying a few more fans and more ventilaton. ive been looking for the answer to that Q everywhere for about a week now!!!
Click to expand...
Its really not that hard to find.

Its called "growing Texas style".



J
 
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