Proper Ventilation, Approx. 440 CF Room

[Sinner420]

Now, I'm working on my grow room operation this weekend. This includes installing necessary implements that would otherwise disturb the environment at a later date. What I'm most concerned about at this time is the Inline Fan that I want to buy online (I'm buying online not only because of transportation issues, but prices are just way better). So, with my room being about 440 cubic feet, I was understanding from all that I've read or viewed about ventilation that I would probably want to use a 6" Inline Fan for proper air evacuation. However. Without wanting to have to buy a different fan at a different date, I wanted some opinion on this question; Is it really necessary to evacuate ALL the air in the room in just one minute? I mean, because my operation is legal and I'm only allowed to grow up to 12 plants total (in all stages of growth), is it really necessary to have 440 CFM of pull? I mean, It's not a huge price difference from a 4" Inline, to a 6", but I don't really want to spend what might not be necessary. Also, in the near future, I will be putting a 3'x3'x6' tent in the room for veg or budding because I won't be able to achieve both in the same light space (different light cycles). So, I'll probably add another fan to use just for the tent, then upping the CFM pull throughout the room, hypothetically. Another small issue is that because I rent the house I'm in, I can't make any drastic changes by making a new hole for the air to evacuate the house, so, I'll be using the dryer vent hole that is not in use presently. This is 4", and I was thinking of back-flow possibly harming the function of a 6" fan, even though the duct wouldn't be reduced until the out-take point of exit.
Alrighty experts and novices, tell me what ya think!! I'm heading down to work on the room soon, so I'll get back to any comments as soon as possible. Thanks for any help and Happy Holidays!

~Sinner420

 

[Tom Bombodil]

Hey sinner, cute babies u got there!

I'm fairly novice myself, but it seems like what i originally heard to be change the air "once every 2-5 minutes" sometimes gets repeated as "2-5 times per minute". I suspect that in the repeating the numerator and denominator of that ratio have been flipped... Im sure someone is going to disagree with me here and insist that it should be several times per minute, but the plurality of opinions seem to agree that "once every few minutes" is the way to go. So that means somewhere in the 200cfm range should do it.

More experienced ventilators, please chime in!

If it were me, I'd get the 440... You mentioned that you've already got plans for expansion, and you are right that the price between the 4" and the 6" are not large.

 

[Sinner420]

Boy, it's been a while since I wrote this! Since this post I've moved and my grow room is now a 9'x9'x7'. Lucky for me I got a great deal on a grow tent off Craigslist (3'x3'x7'). It came with a 400 watt H.I.D. light fixture, air cooled hood with reflector, digital ballast, and Hortilux Blue MH 400 watt bulb (used). Also got a couple light hangers with it, a 6" can fan @ 250 cfm, and a 1" clear water pump (which I didn't need, I'm using soil) the guy threw in for an extra $10.00. I couldn't pass that up. All this stuff for $210.00 total! In the end, I had to go online and buy a new bulb, a Sodium 400 watt. Found a pretty good one for $18.00. It had a decent spectrum and seems to be doing quite well.
My current issue dealing with the ventilation is that I don't know what I want to do with this 6" can fan. I've been using the 4" inline fan that pushes/pulls 190 cfm as a outtake and bulb cooler from the start. It has to vent down about 25' of pipe, but there isn't much I can do about that unless I want to just outtake into the basement, not outside. Of course, I used a 6" to 4" reducer flange to be able to vent because the air cooled hood has a 6" hole on either side. Now, soon as the weather gets a bit warmer (I'm in MI) then I'm considering changing the whole ventilation setup, starting with using the 6" can fan to cool/outtake the tent, room. If I do that, then I think I will use the 4" inline fan to pull fresh air from the outside, or inside the house, into the room. I'm just not sure what would be best yet. I can tell you that my relative humidity hasn't been a big issue, but it does get as high as 83% for short periods of time. I'm going to try and draw up a diagram of my room and post it in the next few days, it may help me to show others what I'm dealing with, enabling ya'll to help me out better with this decision.
I know that air is one of the very important elements in a good grow. My next cycle is some awesome Grand Daddy Purple and I really want them to flower and bulk up good. The only way this is going to happen is if I get optimal ventilation, lighting, and watering, which hasn't been a problem (watering). We'll get back to ya's with a diagram soon. Until then, anybody got any ideas???

 

[Tom Bombodil]

Hey sinner, congrats on the great deal you got.

If you have both a 6" and a 4" fan, you may consider setting up a completely independent air ventilation system that handles your heat, and then a smaller ventilation system that handles the air exchange for the plants. The heat generated by the lights requires a much higher volume of airflow i think, while the plants themselves only need a air exchange every 0.5-5.0 minutes (depending on who you ask).

I've currently got a 6" hurricane fan (460cfm) cooling my 400w light and a small 120cfm axial fan exchanging the room air. At this time they both exhaust into the main room that the flower chamber is built into, flower chamber is 3'x5' footprint inside the 10x12 main room, so basically the main room I'd functioning as a lung room for BOTH the light exhaust and the plant exhaust... Works great for me, maybe because of the relatively small ratio of flower room size to the main room size.

The 400w doesn't need all that airflow in my opinion, i got the 6" 460cfm hurricane for overkill and also with Assn eye towards future expansion. In your situation, using a 400w light in a much larger flower room (9' x 7' ft? ), you may consider reversing what I'm doing and use the smaller 4" fan to cool the light and the larger 6" fan to exchange the air in the room. That's what I'd do, my only uncertainty would be the long 25ft run of vent... May

 

[Tom Bombodil]

Prove to be a bit much for the 4" to push or pull... If that turns out to be the case, just try reversing it and using the 6" for the light, i think the 4" would be just enough for the plants air exchange if heat was handled by the 6". 9x7x8 (assuming an 8 ft ceiling) means 264 cubic feet of air, so I'd say anything around that volume per minute or higher would do the job for you allowing for some efficiency loss due to ducts and bends.

Please let us know how its going, or maybe you've already designed a plan since this last post. Good luck sinner buddy!