Noob - DIY Growbox Critique

Hi GrassCity,

I'm always a bit nervous posting as a noob, but after trolling the boards for the last few months, I figured it was time. Believe it or not, I started my build as a substitute for the bad lighting my garden was receiving on my patio. Before I knew it, I had a full-blown negative pressure setup, built from the ground-up through trial and error.

Anyway, I would greatly appreciate any critique from the experienced and novice horticulturalists on the boards regarding my particular setup. I feel that I have done sufficient research, even some testing with various flowering and fruit-bearing plants, to merit a step up to the real thing. So flame if you must; I am a noob after all, but I hope some of those comments are at the very least followed up with some useful suggestions.

I have included a picture of my cabinet as reference with the specifics listed below. Thanks everyone!

-Dimensions: 4'x2'x4'

-Lighting: (1) 600w HPS/MH, housed in (1) CoolTube with reflectors; 6” diameter openings

-Ventilation:
(1) 450cfm centrifugal fan connected to (1) fan speed controller, sucking air from outside (RIGHT SIDE) the box and through the light fixture to keep the temps down.
(1) 250cfm inline fan (sold as a standalone inline, but it is definitely a booster) connected to (1) carbon filter dumping the exhaust out the top. All seams are sealed, so negative pressure is achieved through a passive intake vent measuring 3”x8” located on the bottom right.
*To clarify, I have the heavier fan sucking air through the light for temp control, and the smaller of the two facilitating the air exchange through the passive intake and exhausting out the top through the scrubber.

-Medium:
​(1) 1.5 cubic foot bag of FFOF
​(1 each) Dr. Earth nutes for flowering and vegetation
​pH buffers, testing strips, moisture meter, micro lens, etc.
​
-Other:
*(1) rigid stainless steel screen (not pictured) for ScrOG (2”x1.5” grated openings)
*6” diameter ducting all throughout
*Reflectix Double-Bubble Foil insulation
*High density rubber foam insulation tape (1” width); seals doors and large gaps measuring >/ ½”.
* (3) 5-gallon buckets for later use, contingent on the success from my first attempt.
*Polyurethane sealant applied to joints and cracks measuring < 1/2”
*(2) Heavy-Duty analog timers rated at 1700watts each
*(1) Humidity/Temperature monitor docked at plant level; out of direct light or heat – for accuracy.

I have my concerns about the bubble insulation as well as with my choice to use the smaller fan exclusively for scrubbing. From what I have gathered reading through the forums, the bubble insulation works great as a sound dampener but I'm afraid its too efficient at retaining thermal transfer within the box (higher temps). It was not exactly cheap so I would hate replacing it with equally expensive Mylar, but if that's my only alternative, so be it. As for the inline fan, I am fairly confident that the “booster” is not pulling 250cfm's, leaving me to wonder if I could get greater air exchange, thus lower temps, if I swap the fans' duties (450cfm on the exhaust, 250cfm to cool the light). Thoughts?

I hope I'm not asking too much as a first-time contributor; I'm just eager to share what I've learned from the folks repping GC. Thanks guys and gals.

 

Posting from my phone had its challenges. Updated with specs and pictures

 

Thanks for the feedback! With regards to your suggestions, unfortunately my build is located in my garage; beach climate. So you can imagine how hot it can get in there, one test run recording interior temps of 92F. I've read that some strains can actually thrive off such high temps, but I am definitely not going to test that theory. I settled on cutting a 1"x3" lateral opening in the aluminum ducting leading to the first opening into the light fixture. I then covered it with carbon filter and sealed around the patch filter. There was an instant increase in circulation as well as a noticeable increase in suction from both the passive intake and facilitated exhaust entry. My only concern now is that I may decrease the efficiency of the carbon filter if the negative pressure nets too high. So long as this mod keeps my temps down, fixing a poor air scrubbing is a piece of cake.

In terms of soil and the buckets, my thoughts exactly on the soil suppressing light leaks. I'm not sure if my picture shows it, but I have the buckets cut about an inch short on the bottoms and supported by high tensile mesh screening. I then have the bottoms sealed back up and leave it to physics and a semi-elaborate tubing systems feeding the run off outside.

So currently, my only main concern is keeping my temps down. If my modification on the ducting doesn't work, my next option is to adjust my "day" photo periods until I have my light running during the cool night time hours and my darks during the hotter parts of the day. My absolute last resort would be rigging together something to funnel the consistent breeze that blows across my garage into the intake chamber. In a nutshell, it's means that ill have to do a lot more work. Cheers.

 

Thanks! Check out my grow log if you get a chance and let me know what you think. Maybe you can add something from your recent grow. Im going to need all the help I can get.
 
 
Strawberry Dream - Indoor Grow