For anyone using a grow tent for propagation of veggies or flowers:
I was thinking 4’x2’, and tall enough for 3-4 layers and storage top+bottom, but maybe that thinking is flawed. My wife propagated about 400 flowers last year, in addition to a few flats of veggies. Apparently she wants to expand this year 
i have a vivosun i believe is 6’ x 6’x 6’. i like grow tents because you can pipe excess moisture thru tubbing out a window so it doesnt cause a problem in the house. also contains the grow lights light inside of it so it doesnt anoy you. that light is also bad for your eyes. much easier to control temps as well. id go double the size you want as its not as big as you think in there. they get crowded quick.
I just bought a 2x2x4 grow tent and an appropriately sized LED light. I hear the argument for get bigger than you think you need, but this still represents a doubling of my under lights seed starting capacity, and it fit the budget better. Where I think it might be coming back to bite me is ventilation. I hadn’t really considered ventilation systems before I bought it, and it seems like even the wimpiest ducting fans would be overkill considering one of my primary goals for the grow tent was to have a spot that’s a little warmer than the house around it. From what I’ve read, you want the air to exchange at least once every 5 minutes, preferably every minute. The weakest fan I can find would exchange the air volume 5 times a minute! Not sure how I could keep anything warmer with that. I’m sure I can figure out a solution that doesn’t take too much energy, but I’ve got some thinking to do. @steveb4 any suggestions?
Depending on the fan type, reducing the input voltage into the fan will reduce the rotation speed. There should be some variable output power supplies out there.
I have seen those. Still debating based on budget. I have been thinking about just letting convection take care of it, since I’m only doing seed starts and some cuttings instead of growing out full-size plants. I don’t know what the CFM is, but I was able to see dust motes getting sucked in pretty quickly with the light on and one high and one low vent open. I expect a tray of 4" seedlings has lower CO2 needs, but I may just be fooling myself.
Edit: I’ve since estimated the flow at 4 CFS by looking at how far the dust traveled in 1s at the intake and knowing the opening size. The formula for flow is Q=V*a. Q is flow, V is velocity, and a is cross-sectional area. I estimated about 3 in/s over an opening of 40 sq inches. That comes out to 15 ft/min and 0.28 sq ft. 15 x 0.28 = 4.2 CFS. I rounded down to 4, but I wouldn’t be surprised if it was a smidge higher, as air is probably coming in from a lot of other small gaps, and I was trying to be conservative with the dust speed.
That comes out to changing out the air volume every 4 minutes. However, that is with the light on its highest setting, and no fans or other appliances inside. I expect it would run more slowly when the light is dimmer. Also, I have a feeling adding a circulating fan might mess up the smooth convective flow of air.
I think I saw someone using a computer case fan that runs off USB (cheap amazon buy)… maybe it’s flow rate would be a lot less (at least in my mind, should be fine). Practically speaking, I think if you setup the fan as a push (versus pull) you should be able to reduce the flow further, including by partially obstructing the outlet (or inlet). Or you can put a longer tube on the inlet or outlet to increase turbulance and reduce airflow. Just a few thoughts.
Thanks for the link! I’ve been looking at that sort of thing, too. The trick is a) connecting it to ducting (relatively easy) and b) finding it not on Amazon for a reasonable price (relatively hard).
Try searching amazon, home depot or home depot on “duct flange” or “duct collar”. You might have to make an adapter plate to go to the fan, which would be easy if you have a plywood scrap, saw, drill, and a few screws.
All that said, this is an awful small space. If it was me (and I haven’t used grow tents before, which is why I posted this up originally), I’d just cut a hole the size of the fan and mount it to the tent… it’s light enough. We use grow lights, just no tent yet… don’t think you will have mass humidity or other issues with this small setup.
If I go that route, I’ll probably build something out of a flange or collar or PVC. Also, I’ll probably go with this fan. It’s a little pricier, but it plugs in directly to AC power. And best of all, I don’t have to fund private rocket joyrides.
if youre growing seedlings, just leave your vents open and have a 10in. fan blowing over them. thats what im doing with mine right now. seedlings like high humidity anyway and as dry as the air is this time of year, i dont think humidity would be a issue. if you dont have room for a fan you can hang it from the top supports.
Thanks! I suspected that would work, but it’s nice to have confirmation. Most of the online info on using grow tents seems to assume you’re growing a crop of cannabis from start to finish. I understand the historical reasons why, but it makes it hard to find info on any other type of growing.
yeah a full sized plant in there would put out alot more humidity than a few trays of seedlings for sure. even some smaller plants are ok with just the desk fan in there.
I’m getting a fan that I can clip to the support poles. Once I have that, I’ll run that and my light with the vents open and see how the temps are. If it still needs a little extra heat, I’ll try the aquarium heater in a bucket trick, or even just running a seedling heat mat.
I’ve been thinking about this also. I have been starting seeds on narrow shelves I have made to go across a window in the house. When it warms a bit outdoors I made lampshade size coverings, round about 16 inches in diameter by 14 tall with 1/2 inch wire mesh then covered with greenhouse film and used shade cloth for the top. I put my small plants or seed starts on heat pads and cover with the enclosure. Mini heated breathable place. This year I plan to arrange a small closet in the garage to start seeds. It’s about 5 x 8 feet with a door. Add a small radiator heat source and my grow light. Safe from my indoor cats.
Yes! That’s the other major driver for the grow tent. Now I just need to do something about the squirrels.