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what size passive intake with 8" vortex?

Guayaki

Guayaki

Member
in the past I never had passive intakes. I just never caulked around the edges of my 4'x8' box and the door wasnt closed real good. Now I got it all caulked up real good, door has no leaks or anything and all my lights are vented. The box is 4'x8' and is 7' high. I am venting with a vortex with a scrubber and was wondering what size the passive intakes I should make be? I was thinking around (2) 3'' holes but what are you using or what sounds about right? Thanks guys!
 
FreezerBoy

FreezerBoy

Was blind but now IC Puckbunny in Training
Veteran
General rule is intake should be 1 1/2 to 2 times larger than exhaust. With three inch holes, you'll want at least four, maybe six.
 
Guayaki

Guayaki

Member
wow I thought it was always less than the exhaust so none of the stink would escape. having less or an intake making everything in the cab would eventually be filtered. glad i asked. :)
 
S

snadge

Member
FreezerBoy said:
General rule is intake should be 1 1/2 to 2 times larger than exhaust. With three inch holes, you'll want at least four, maybe six.
Click to expand...

I was always told 5-7 times the area of the outlet depending on the cfm of the outlet fan, remember it is a passive intake with an active exhaust.

cover the inlets with activated carbon sheet that you can buy for cooker hoods as well, stops any smells leaking out and stops the nasties getting in, I use a 1cm square mesh taped either side of the activated carbon sheet to give it rigidity when covering the intake holes.

Saying that you won't have any smells leaking out if you go nearer 5* area due to negative pressure.
 
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G

Guest

Guyaki:

An 8 inch Vortex has an opening of 157 square inches. A 3 inch hole has an opening of 22 square inches. Apply the math as you see fit regarding the actual number of holes you will make.

A single hole of at least 8" diameter (not an 8" square one which only has 64 Square inches of opening) works good.

In my grow room there is an 8" carbon filtered exhaust and a 6" inline fan fresh air intake. No problems at this end with an intake that is smaller than the exhaust, of course it is not passive either.

Happy Growing and Peace

TyStik
 
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simpleword

simpleword

Active member
Ty-Stik said:
Guyaki:

An 8 inch Vortex has an opening of 157 square inches. A 3 inch hole has an opening of 22 square inches. Apply the math as you see fit regarding the actual number of holes you will make.

A single hole of at least 8" diameter (not an 8" square one which only has 64 Square inches of opening) works good.

In my grow room there is an 8" carbon filtered exhaust and a 6" inline fan fresh air intake. No problems at this end with an intake that is smaller than the exhaust, of course it is not passive either.

Happy Growing and Peace

TyStik
Click to expand...


Somewhere your math went a little wrong. A square with the same dimensions of the diameter of a circle will always have more area. A 8 inch diameter circle has 50.26 sq inches of area, as opposed to 64 for a square.

squircleil2.jpg
 
H

hydroflower

Member
You can do it this way, cut holes to an area equivilent to 5 times the exhaust diameter then put your hand in front of the outlet and feel the force of the air rushing out with the door open, this is the fans maximum air flow with no restriction, then shut the door. With 5 times the area you should be feeling little or no reduction in force than with the door open. If you feel as though there is less air exhausting you can cut more holes. This allows you to control the air exchange in the grow by covering and uncovering them as and when you need them.
I always find the more adaptable the grow the better in regard to climate control.
Remember you will need to make up light traps over the inlets to stop any light getting in.
HF
 
G

Guest

Now that the stone has worn off I realized that I multiplied pi x r x the resulting number, NOT pi x the radius squared (16), Thanks for the correction SimpleWord.

TyStik
 
TGT

TGT

Tom 'Green' Thumb
Veteran
When I use a passive intake I always make sure it is not too large as to diminish my vacuum that I create with the scrubber/fan. This is created by exhausting more air than is pumped in so the exhaust should always be stronger than the intake. Smell escapes otherwise.

Usually what I do is with the room sealed, door closed and the carbon scrubber running, I cut a hole for the passive intake to the size I think will be needed. Then I feel with the back of my hand if that passive intake is pulling air in. If you blow some smoke near the intake that will work well too. If there is enough of a suction that I can feel it fairly strong, it should be fine. If not I seal up half the passive intake and repeat. The more suction the better for keeping smell contained.

If there is a good pull then even if there are cracks and leaks in the room or cab, it will only pull air into the room and not leak out. Hope I didn't make this more complicated than it need be. I got a habit of doing that. I hope someone didn't already mention this exact thing. The words are starting to get blurry. Hope this helps.

TGT
 
FreezerBoy

FreezerBoy

Was blind but now IC Puckbunny in Training
Veteran
Guayaki said:
wow I thought it was always less...
Click to expand...
Depending on your circumstances, it doesn't HAVE to be larger. I used matching holes for years with my 150 HPS. When I upgraded to a 250 CMH, heat buildup forced my hand. With 2x intake, my temps are under control and I still have negative pressure.

Thing to remember is that intake is the limiting factor. You can't suck out more air than you bring in. Unless you're using CO2, I don't know that there is such a thing as too much fresh air as long as you maintain negative pressure to contain smell.
 
pineappaloupe

pineappaloupe

Active member
If you have some extra cash to spend look into darkroom quality louvers. I have 2 6x6's made by Doran. They are great. I think there is a 12x12 version... some even have fans.
 
Guayaki

Guayaki

Member
Thanks everyone for the answers. I understand it all a little better. I ended up doing 4'' holes instead of the 3''. I made 6 of the 4'' holes and stuck that pvc piping in them that has the threads on the end. I got those caps that I can screw into the threads so if I need to cover 1 or 2 up from stink leaking out I always can, but this seems to work pretty good using all the holes. You get a nice little air-flow threw this sucker now. I think I can actually take my wall fans down but I will leave em up for now. so thanks for the answers.

Pineapple I just looked those louvers up and they sure are cool looking. Already got the pvc in and rocking but if I end up getting light leaks I got a page bookmarked that sells those louvers. Didnt have a price on that page but can't be too outrageous.

Thanks again!
 
M

Microwido

Also, goto to Lowes and pickup an Alergen and smell reducing furnace filter. This filter has a carbon layer, and then a regular layer. I cut it up into 6 even peices, and used 3 to cover my passive inlet. I used 3 carbon layers back to back and then 2 regular layers and duct taped it all up. This is a cheap and effective smell / light / particle Filter.
 
Guayaki

Guayaki

Member
excellent thanks for the info micro. been to lowes 3 times in the past 3 days. lol every couple days I always have a list of things to buy and just added another. take it easy.
 
icough2getoff

icough2getoff

Active member
yeah those darkroom vents are nice. I have two 8" doran brand louvers and with my 6" vortex on low setting my cab doors get sucked shut. When I've sat inside my cab the airflow was quite lovely.
 
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