Grow Room Passive Air Intake ...

[Chester]

I read that the correct size for a passive air intake is 3 times the diameter of the fan. So a 6" fan would require approx. 18" of passive intake. Seems like a bit much but they are probably thinking about the fan running full speed. I use a 6" fan on low speed and I have 2 x 10" ducts on the bottom of the tent. I would like to find a way to open two ducts on the bottom of the tent w/o light escaping that filter the incoming air. My idea would be a 4" piece of 8" ducting that has a blackout air filter on one or both ends. Has anyone tried something similar or do you know where I can buy one. Currently, I use an elbow from a 6" duct w/ a filter over one end, for my air intake. Sticks a little far into the tent and does not block the light very well. Any tips or ideas will be appreciated.

 

[growingmicro]

Any pics?

 

[growingmicro]

I don't know about that rule, but I've seen somewhere a diy for a light blocker and works something like this you can add some "lips" every other way and it would block it. Thinking about it now maybe if it had a third one on top it would be better, also works best with non reflective material/color.

 

[Death The Cultivator]

I read that the correct size for a passive air intake is 3 times the diameter of the fan. So a 6" fan would require approx. 18" of passive intake. Seems like a bit much but they are probably thinking about the fan running full speed. I use a 6" fan on low speed and I have 2 x 10" ducts on the bottom of the tent. I would like to find a way to open two ducts on the bottom of the tent w/o light escaping that filter the incoming air. My idea would be a 4" piece of 8" ducting that has a blackout air filter on one or both ends. Has anyone tried something similar or do you know where I can buy one. Currently, I use an elbow from a 6" duct w/ a filter over one end, for my air intake. Sticks a little far into the tent and does not block the light very well. Any tips or ideas will be appreciated.

The result is intake port should be twice the size of the exhaust. Maybe with panty hose would be sufficient

 

[BII]

113

I read that the correct size for a passive air intake is 3 times the diameter of the fan. So a 6" fan would require approx. 18" of passive intake. Seems like a bit much but they are probably thinking about the fan running full speed. ..........

This 3x guidance for air intake might more logically relate to the pipe's cross sectional area ('pie' x 'r-squared'). For example, a 6-inch diameter has area = 28 sq. inches, and 8-inch diameter area = 59 sq. inches.

I don't know about that 3x guidance, but to me going up 2-inches in pipe diameter should be good enough.

 

[pop22]

in a grow tent, negative air pressure is recommended. The standard intake ports are fine as is as relates to flow control. And the purpose of the air exchange rate is not for environmental control, its to maintain CO2 levels.

 

[bad dragon bzzz]

i read a lot of stuff about weed and growing some cracking theories and bits of info.A lot of old wives tales and botched experiments.
So at the opposite end of this theory of x3 the exhaust.My cupboard with a 4" exhaust has next to no intake,an ill fitting door,or the cracks in the door are my intake.So if my intake is divided by 6 rather than multiplied by 3 the only conclusion we can come up with is my cupboard air exchange/flow must be misserable.
Maybe it is maybe theres more to this x3 theory than meets the eye
good luck n keep er lit

 

[Olderfart]

3x? I doubt it, at least as far as providing co2 to plants is concerned. This spec seems more likely to me to relate to achieving next to zero reduction in maximum cfm of air that can be moved by an extraction fan. Likely a means to defend inflated or irrelevant cfm specs.

I already have my fan turned to its lowest setting, have added a baffle to reduce air exchange further to keep humidity high enough, and my intakes are mostly through cracks around my doors and covered air intakes. Why would I want a massively larger passive intake?

Air only needs to be replaced at a rate which will provide CO2, and in some setups, to reduce RH or control temperature. Excess exchange beyond that, or the ability of intake size to achieve it is, I think, irrelevant.

 

[pop22]

Here's what AC Infinity has to say about this:

https://www.acinfinity.com/blog/how-to-calculate-required-cfm-for-a-grow-tent/

 

[Olderfart]

Here's what AC Infinity has to say about this:

https://www.acinfinity.com/blog/how-to-calculate-required-cfm-for-a-grow-tent/

By any chance do you know where I can get my mitts on measurements of CO2 levels in a tent being ventilated at various rates? I find it a bit puzzling how my plants would use a significant portion of the CO2 in the growdrobe in one minute, which seems to be the assumption behind ACInfinity's recommended ventilation rate. In any case, it seems to me that it is not the volume of the grow space that is the issue, it is the amount of live plant tissue being fed CO2, which may be more related to occupied floor area than total grow space volume.

I am pretty sure that I am exchanging air at much lower rates than suggested, and my plants seem happy. Perhaps they would be happier with more air, but supplying more would mean humidification that I would rather not fuss with given that I do not see a problem.

Thanks for the link.