Quick ventilation question (about to order a fan)

Discussion in 'Growing Marijuana Indoors' started by HighOnTheHill, Jun 9, 2009.

  1. Grow cab is 22" x 31" x 61"

    So that's 24ft^3

    I was just told that a 268 CFM fan WILL NOT do the trick as far as cooling my cab. At least without a cooltube, which I'm not using.

    So I'm looking at a 565 CFM fan, and am about to go to WalMart and get one of those MoneyCards and order this shit.

    The fan is exchanging the air 23.5 x per minute.

    Is this going to keep a 400w HPS cool? No cooltube, just straight venting right outta the top of my cabinet.
  2. I think a 286 CFM fan is already overkill in such a confined space, I would definitely not go any higher.... and even if you did, and I'm wrong, then you can add a second fan. Used to be in the residential HVAC biz for about 10 yrs.

  3. Okay this is totally getting frusturating. I wanted to order it today, but I don't know what's going to work and what's not.

    I was told that 565 CFM isn't even enough without a cool tube =/

    There's a guy Amoril (I think thats right) who's growing in a space slightly smaller than mine, with a 400w HPS with no cool tube running a 700+ CFM fan and his temps are at 78 degrees.

    Then again, the 565 CFM fan... err, well. Half the websites you order it from claim 700+ CFM for the same fan, cant remember the exact number. Wish I woulda seen this post an hour ago, but I've been busy trying to fix my pH.
  4. Well, I have a friend, just for comparison: He has SIX 1000W lights in his room. He runs his cool lights for 5 of them (one is in the veg room not hooked to it. The complete room is 29ft by 8ft with a height of 7 ft. He has ONE fan handling all of it. This is ONE 1000 CFM fan. He has been running this for about 3 yrs. and is thinking of re-doing the room and would like to add 5-600 CFM to what he uses now.

    If you put a 500 CFM in your grow area or cabinet, you're gonna have to tie the plants down so they don't fly out the exhaust..... I'm exaggerating of course, but believe me it is overkill.

  5. IMO, get the biggest fan that you can afford, and get a speed controller. This allows you to turn the power back, reducing the cfm and indirectly the noise, if noise is a problem.

    after the speed controller, Im probably running about the 550cfm mark.

    BTW, its not so much airflow that I cant work with it. Like I said in the other thread, I had to add bars running along the sides of the tent to keep them from going concave on me (vacuum in the tent is strong). Once that was accomplished, the plants just look like theyre in the path of an oscillating fan....

    imo, its a good thing to have plants moving lightly from air circulation. Helps in a ton of ways....mold/disease resistance, stronger stems, etc.

    you can always turn a fans speed down, its much harder to increase it ;)
  6. also, just wanted to point out something that I thought about. youre making all these comparisons, trying to solve your problem...which is cool.

    but, youre not asking one very important question.

    what is the ambient temp / temperature of the air on the intake. This is going to be your hard cap on temps....in all practical purposes, youll be doing awesome if you get within 5 degrees of this temperature.

    so, when I hit 78, you have to consider that we like our A/C units where Im at, and use them frequently, cause it gets HOT. Oddly enough, it was mild the last few days, the a/c wasnt on as much, and the temps were low 80s periodically. Im ok with that, just pointing out how much room temp plays a role in the grow temp.
  7. You will want to be careful if you use a dimmer or speed controller. with many/most fans you can cause damage to the winding of the motor when not run at a different RPM than it was manufactured for. .....Amoril is correct that wind is good for the plants, as well as the temperature cap in regards to temperatures. Good luck!
  8. A variable speed fan controller from a hardware store works great. Controller for a motor not a light.

    Amoril has it down to get a bigger fan and run at half speed. Much quieter.

    Consider building a simple box around the fan. Won't take much mass to stop the sound emanating from fan motor and blades.

    Attach the fan with bungees or some other "lossy" technique. This will significantly reduce the vibration conduction.

    If the exhaust portion is too loud, consider transitioning from say 6" duct to a 12" boot at the end. The radical increase in duct volume will slow the air considerably, creating a cheap muffler.

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