Is my micro-grow too big for PASSIVE INTAKE?

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maoriJane

Member
I've scrapped my closet grow & decided to embark on a micro, inside the hull of a floor-standing portable air conditioner. It's just a bit bigger than a p.c. grow.

My question is, will I need an intake and outtake fan, or can I get by with just passive intake?

I plan to use six 22 watt CFLs (for low heat).
I plan to use a 4" inline fan (with carbon scrubber at flower time) for outtake. (190CFM -- is that way too much for a small cab?)

The dimensions of the cab are:
26 inches tall x 19 inches wide x 11 inches deep

...Also -- if I use passive intake, will smells seep out at flower time?

I'm a rank beginner, so I appreciate any help. THANKS!

ac1.JPG
 
Penyajo

Penyajo

Well-Known Member
Your going to need an intake and an exhaust. Ventilation is a HUGE contributor to healthy plants. STAY HIGH!!!
 
M

maoriJane

Member
Penyajo said:
Your going to need an intake and an exhaust. Ventilation is a HUGE contributor to healthy plants. STAY HIGH!!!
Click to expand...
Thanks for the answer. But in small spaces, like microgrows doesn't a powerful enough outtake fan create air flow enough for ventilation (even with passive intake)? I kinda expected to hear that passive intake is okay, since my space is small, but my outtake fan (190CFM) is too powerful.

If I use intake & outtake, do I need they need to be the same strength, or does it matter?
 
maariic

maariic

Active Member
It shouldn't be too hard to reverse your intake as exhaust. Just flip over the vent. I am not very great expert, because of second grow only. But I have read that exhaust always has to be a lil bit more powerful than intake. So passive intake should be better that passive exhaust. Or am I wrong?

EDIT: FCUK I am wrong. I understood you have only intake fan. I think it is enough to have only outtake. I have this order as well. And it works.
 
Bluejeans

Bluejeans

Well-Known Member
If I remember my math right, you need a minimum 31cfm fan for that size area. With 190 cfm pulling out of there, I would think that passive intake should be more than sufficient. I have a 23" x 24" x 16" box, which, by the same calculations, would call for a 49cfm min. I have a 225cfm 3.5" outtake fan in my box and it has been perfect. Don't worry about it being too much. Too much is really more of an "intake" concern because you end up blowing the heck out of your plants.

I don't have the carbon scrubber on mine so I can't speak to the smell issue...as I've said before, where I'm located, it isn't an issue. However, with 190cfm pulling out, I'd be very surprised if any smell leaks out through the passive intake.
 
weedsgood

weedsgood

Active Member
in my micro pc grow i have 2 60 watt cfls and 2 100 watt cfls and only one intake fan. temp stays under 75 degrees and the plants are pretty healthy :)
 
maariic

maariic

Active Member
weedsgood said:
in my micro pc grow i have 2 60 watt cfls and 2 100 watt cfls and only one intake fan. temp stays under 75 degrees and the plants are pretty healthy :)
Click to expand...
Do smell for you is an issue? If not then it's OK to have only intake fan. But if you are trying to avoid smell, you have to filtrate your air flow and passive outtake will lead to pressure inside the box which will try to find leaks and go the easiest exit rather that filter.
 
M

maoriJane

Member
Thanks everybody. Just the sort of info I was looking for. Btw, if you can get your hands on a junked portable ac, grab it. Seems all but ready-made for a stealth cab micro grow. The tube you see on top in the first pic is for the ac to vent hot air out the window. It's just a bit over 4" in diameter, which I think will fit my fan & filter nicely. The "ac" is great stealth cover for the fan noise too.

They come in taller sizes too if you need more space. Mine is small, but still actually pretty roomy inside. Plenty of space to keep me in bud, if it works.

ac1.JPG

cab.JPG
 
Bluejeans

Bluejeans

Well-Known Member
OMG that's awesome! You're right, it does appear perfect for a stealth grow. And oh my, it's a DIY wet dream. What I could DO with that! Can I come over? LOL... Seriously, great find and super idea. Now I gotta find me one of those. I don't even need stealth, but that would just be fun to build. I would +rep ya, but apparently, I gotta share the love before giving to you again :smile:
 
Voidling

Voidling

Well-Known Member
Don't forget that you can get a fan speed controland slow the fan down if it's pulling too much air through.

Passive intake will be fine but want 2x the surface area on intake to exhaust.
 
Penyajo

Penyajo

Well-Known Member
The only true way you are going to be able to tell is if you do a test run. Put you lights in there and put your exhaust in there and try the passive. Run it over night and see what you thermometer reads throughout the night. Check your highs and lows. I tried to do a passive intake on a box once and it didn't work out to well. And I was using 265cfm exhaust. STAY HIGH!!!
 
Bluejeans

Bluejeans

Well-Known Member
The main key to passive intake is to have adequate venting for the intake to occur. You can control where the air comes in primarily by design and placement of vent openings.
 
Beefbisquit

Beefbisquit

Well-Known Member
With 190CFM flowing through that tiny little AC unit you don't need to worry about intake, it will suck air in from every friggin crack or space on that box... Just make sure you have vents at the bottom of the box, you still want to direct the air. Control is important. I'm using passive intake on a 40 cubic foot tent, with a 160CFM 4" inline fan. Works great, moves a ton of air, creates exceptional negative pressure.

Please tell me you have a fan speed controller, lol...
 
M

maoriJane

Member
Beefbisquit said:
With 190CFM flowing through that tiny little AC unit you don't need to worry about intake, it will suck air in from every friggin crack or space on that box... Just make sure you have vents at the bottom of the box, you still want to direct the air. Control is important. I'm using passive intake on a 40 cubic foot tent, with a 160CFM 4" inline fan. Works great, moves a ton of air, creates exceptional negative pressure.

Please tell me you have a fan speed controller, lol...
Click to expand...
No I don't. Have no experience with fanspeed, so I didn't even think about it. I ordered this one: http://indoorgardening1002.info/new-hydropronic-4-inline-fan-with-carbon-filter-combo-odor-control-air-quiet.htm

Where did you find your lower speed fan?
 
Voidling

Voidling

Well-Known Member
I'm not sure if that would need a Pam modulator or not. I've got a fan sitting here I need a pwm dimmer for.

Plus side of slowing it down is even less noise
 
M

maoriJane

Member
I'm reading that slowing it down makes it even noisier, if you use the wrong fan controller. Anyone know of a good brand?
 
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