Ready to start building! - final opinion from you wise growers please?


420 Member
Hi everyone, first time posting here — have read and read regarding building my first grow box but would still appreciate some opinions from those more experienced, before I go creating vent holes, buying fans etc. No photos I'm sorry as it's all in bits and pieces still!

Main Q is to do with ventilation — what sizes you'd recommend for intake/exhaust and fan size/CFM.
My box is small: ~95x60x50cm or ~3.1x1.6x2ft = 10cubic ft approx. Planning on single plant grows.
Plywood box and going to use soil.
Light: Supergrow LED Halo only 25W, but 420-720nm and I have read this should do for a single plant.
Was thinking that a small fan and CFM would do with the small size of box and not expecting too much heat from LED light. Was thinking one exhaust vent with in-line fan, one intake vent with passive intake only (with HEPA filter/lightscreens). There can be no odour so planned on internal carbon filter attached to exhaust fan (sucking through filter direct to outside box). I like the look and reviews for Noctura or Silenx fans.

So, small box, minimal heat from LED — ventilation is more for air circulation than removal of heat so I figured a 4" exhaust fan would do and pulling through a 4" carbon filter. Anyone think I should go bigger — 6" with 6" filter? I'm worried too small a fan will not pull through a filter...but also worried if I go too powerful it'll pull through the filter too fast and not give enough time to remove odour. Perhaps stick with 4" but also use a small inlet fan? Also figured if I start with small vent holes, I can always expand them if need be...but can't do the opposite once I've sawed holes in my box!

Opinions on whether this will work, or any other tips from those who are more experienced and wise would be much appreciated, thanks.
Thanks Antics for replying and advice. Now you have me worried! I chose LED in the end mainly because I wanted a stealthy and small grow and figured these were best from my reading, because of low heat and ability to have the lights in close proximity to plants! In fact one of my concerns before reading your reply was how i was going to set up a way of adjusting the height of the light as I figured i'd have to have it low down close to the plant in the early stages! I had read in some threads about keeping a distance sometimes due to yellowing of the leaves yet in most threads/photos I see LEDs right up almost touching the leaves...esp in say PC grows. Also I was just wondering if I needed to get another LED in case one wasn't enough in this space!

Height was chosen based on where I decided to put the box - under a workbench; prob the most inconspicuous place I can without there being a big wooden box just standing there out in the open. You've left me with much to think about. I did a recent outdoor grow of a bag seed and got it to ~4ft tall before bailing out - developed male flowers then seeded like a hermy. Kept about 7 or 8 seeds so may try my box out anyway with the LED on them rather than experiment on my beauty seeds (Herer and Widow). If problems I may have to go CFL.

Thanks again!
Well don't get worried man lol I'm going by information I have based on the LEDs I've seen.

I just want you prepared for the possibility that the light could damage the plants, its going to depend on the light itself, and all manufacturers build them differently, with different components, so it's hard to tell what a light will, and won't do.

Typically, lights of lower wattage run into a problem of not being strong enough to grow Cannabis effectively, but the light you have claims that its a strong light to grow with, so I don't want to say it absolutely won't work, but my gut feeling is that if it does work, yields can be lower than hoped for.

So definitely just focus on a successful grow from seed to harvest, and don't set any expectations as for how much you want to yield. Just grow your best, and let the light do its thing, and see where your yield falls. You can always upgrade in the future. :)

Some LEDs that people use are weak... when I started looking for LED panels, I saw some great deals, $30 for an LED panel with like 100 LEDs and I was all excited, until I read that the light was only 14 watts. That would reduce the intensity enough to where it can touch leaves without damaging them.

Lights all cover a specific area, the LED manufacturer should have those specs. They're usually rated by dimensions they'll cover, like 2'x3' @ 24" height, as an example.

Don't scrap your plans, just be prepared to make changes on the fly if necessary. All grows that test new equipment are the same way, when I first started using my LED, I had to deal with adjusting the light to the correct height, when I first started using coco, I had to start watering daily, and supplementing CalMag. Every change you make requires you to observe the plant closely in how she reacts, and you have to make the best decision based on what she tells you.

It's a never ending learning process, and sometimes things will change from strain to strain. But, it's also fun watching them grow, and rewarding when you can sit back and relax, and enjoy your hard work.

I dont think 25w LED will be enough, maybe if you keep the plant very low. Have you considered side lighting. That will help a lot. In a small box I would have light on top and the 3 sides as well. Your 4" fan should be more than adequate, but I would be concerned about the lack of light. I would maybe put the 25w light on top and line the sides with some red/blue LED strips, they can get very close to the plants without burning and dont put out much heat.
Since everyone gave you pretty good advice about the LED's ill help with fan size.

Your box size is very similar to mine so let me show some pictures real quick,


I used a Passive Air Intake with a lighttrap and filter. For my outake fan my local Hydro store actualy carries pretty high CFM computer fans. This one was labled at 171 CFM, lets just assume 120 CFM. Theae boxes being so small only need like 50 CFM for an air exchange between 3-5 times a minute. With my air being sucked in through my lighttrap and not having a shit load of holes it creates a significant resistance which is why I went with a higher CFM fan. Could easily make a diy carbon filter but im judt using it for veg atm.

In my 2x4x6 tent I use a 4" phresh filter to a 4" fan rated on the box at i believe 190 CFM. Don't be mistake its small for my space and i wish i went with the 6" but it does the job and im sure it would work great for your box but be careful, they take up a lot of room unless it will all be in the outside exposed for people to see.


Again this is a 2x4x6 so be warned, it will significantly reduce the limited space you have. I would consider other options.

Keep us updated and let us know how it goes, and welcome!
SixthEddie great setup.I grow short and wide so your setup is perfect for me.currently growing on 2 sq ft,6-23watt cfls.I miss my hps!!
Hi everyone, thanks for the additional replies and advice/photos! Apologies for the delayed response - didn't get alerts for some reason after Anitcs' last reply so only noticed my own thread again today with more replies, whilst trying to revisit wiring instructions for my fan.

So I haven't made significant changes or commenced building yet as I have still been trying to decide on whether I should cut down my wood to my original plan (small, to hide away under a work bench) or keep it a bit bigger but it would be out in the open and obvious to family, in-laws etc. I bought a Noctura fan 92mm so am going to wire it up to test it out. Been trying to work out a good way to make a carbon filter that will do the job but also that the fan will be able to draw air through - lots of differing instructions out there but many of them make large-ish or heavy filters. My idea is to try a metal pencil holder but to try to keep it light, only use a portion of the capacity to fill with activated carbon, perhaps by using carbon filter pads filling up at either end with the carbon in the middle. Maybe 4 or 5 cm length with activated carbon. I assume I can test it by say, lighting/putting out a match inside the cab and smelling for smoke on the outside, over the exhaust fan outlet? Looking at a nice louvered wall vent to cover passive intake with built in bug screen but was also going to try vacuum cleaner filter material on the inside to keep dust and finer particles out. For light blocking, I thought that over the wall vent, a decorative car hood/bonnet vent cover aimed in another direction, covering the louvered vent.

It's amazing how I think I get my head around something but then further reading just confounds things - am so itching to get going but then I want to get this right. As Antics said, I guess i'll just have to bite the bullet and give it a go and learn from mistakes. I just hope I have enough bag seeds that I can germinate and practice on before I use my beauties...
Thanks again everyone for your advice - much appreciated!
I have revised my plan! Going to stick for now with the smaller box size but use a set of T5 lights - from what I can gather, i'm hoping that a set of 4 x 2" light s will see me right for a single plant in this size box. Gonna keep my LED to experiment with and will no doubt be used at some point, if even only for supplemental light in a bigger box (one day). Will try 2 x 6400k and 2x 2700k. Still unsure if placing lights vertically will be ok vs at the top. Will fit better up the in-side of the box.

Also revised my carbon filter plan - found two differing sized metal pencil cup holders with mesh sides. Going to put one into the other with activated carbon from the pet store in the space between them to maximise air flow/surface area through the carbon.

Exciting getting there - look forward to providing some photos at some point!
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