Input needed

[redtails]

Ok, so let me preface this by saying I live in an urbanized desert, where the temps can be unstable and typically high(even with A/C), as well as avg humidity <20%. Also the components I've listed in the pic are what I already have. I'm trying to make it work with what's available, as I'm on a limited budget, so please don't start recommending something unnecessarily too expensive for this sized grow like a 400w cooled HPS with a 6" vortex fan.

I'm trying to rework the ventilation system and would like to know as many knowledgeable opinions on this as possible:

http://i860.photobucket.com/albums/ab164/redtailsmmj/setup.jpg

It's set up for the most part already, and is in my closet venting into the attic:

http://i860.photobucket.com/albums/ab164/redtailsmmj/101_0600.jpg

I'll be testing it out with a feminized, autoflowering Little Devil from Ministry of Cannabis. Probably one plant at a time with LST to fill out the box. Thanks in advance for your help.

:rastasmoke:

[redtails]

Oh, the exhaust fan has a max cfm of 80 and is routed perfectly straight up through 5' of ducting. I have both a regulator to dial up/down the speed of the fan as well as thermostats to control the fans if needed but neither are hooked up currently.

The intake on the left side of the box is really connected to 20" of flexduct to keep it right at the bulb for fresh cool air.

[jakester]

Is there a question here?

Just try it and see how it goes. It should be fine as long as you have some decent airflow and can keep temps below 95 or so. Get your gear all set and run it with a thermometer and see what it's at.

[redtails]

I guess specifically, are two 2" passive intakes ok for the 4" exhaust?

Yeah, I'll definitely be testing it out first, I'm just waiting for the fan to actualy get here in the mail. Without the active exhaust it gets to about 115 under the light

[DreadedHermie]

Conventional wisdom is double diameter for passive intakes.

So, you might want 2 x 4" intakes to accommodate a 4" exhaust. Bear in mind that bends in the ducts, reducers, and "flex" style ducting add significant "drag" on the system. I'm not sure if your 4" exhaust reduced to 3" counts as 3" or as 4". What size is the fan, and is it designed to "push" or "pull"? (The way your box is set up, you're asking it to "pull.")

Except: 80cfm is such a low flow that your drag may be negligible. However, if you ever need to add odor control, a bigger fan's gonna be needed to drive a carbon filter.

Those intakes/ exhausts are light traps also, yes?

You are going to hate 4' fluoro tubes as side lighting if heat is a problem. For one thing, the diagram shows them also lighting the top of the cabinet, not just plant material. Fluoros do throw some heat, it's just spread out over a long tube. But close 'em in a cab...

I'm curious about the color combo, too. Are you vegging or flowering?

[redtails]

Thanks for the info on intake/exhaust ratios. I'm not sure how much drag the reducer's going to add either but I don't think all that much with the low flow fan. The fan is 4" diameter and I plan to mount it straight to the coupler, thinking that would be the least amount of backpressure?

Yes the intakes have light traps and the closet door will be shut all times as well, unless I'm actually looking in on the plant. Wasn't planning on the exhaust having one as there's no windows or anything in the attic, just a small vent about 50' away that never really get's direct sun.

The shoplights are just an idea, I can toss smaller CFLs on the sides instead if you think heat might be better controlled that way. The colors can be changed, I was planning on throwing them in for flowering.

[DreadedHermie]

Conventional wisdom is double diameter for passive intakes.


That's not very accurate... maybe you knew what I meant. :o

"Double the number of ports" (same diameter) is the recommendation. Looks like your exhaust is actually 3" (with a 4" pickup). So, 2 x 3" intakes, minimum. More is better, if you can keep the light out.

Plan looks do-able; now's the time to test it for ventilation, temps, and light leaks, before you get all green in there. Good luck! :thumbsup:

[redtails]

Thanks for the words of wisdom and good wishes. I've got more 2" ducting so I'll add another of those, effectively doubling the exhaust diameter and maybe another if needed.
The fan should be here tomorrow or monday at the latest so I've got time to test before my planned turkey day start. Got the light leaks taken care of, just need the other two done.