Just another exhaust question.

Discussion in 'Growing Marijuana Indoors' started by whackyac, Mar 25, 2016.

  1. So I have a 4x4x7 (L x W x H) grow tent with a 400w HPS light. Should an 8 inch inline duct booster fan be sufficient for the exhaust in this tent? I also have an 8 inch fan for intake.
  2. I would say yes, as long as you keep the ducting as short as possible as not to impede the airflow. I would also stress that these booster fans stop working after a while, and can be a safety hazard.
  3. That's more then enough

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  4. A safety hazard in what way? As in making the tent too hot and catching fire? I have a thermometer do you think I would be able to catch the fan failing before anything bad happened? Im also only planning on using this fan for around 5 months.
  5. Booster fans are weak. They don't pull their rated cfm unless they're working in conjunction with another main fan. That's why they are boosters.

    In feet lengthxwidthxheight= cubic feet

    If you want to turn the air over 3 times a minute take cubic feet X 3= cfm for an actual inline fan needed to turn the grow space over 3 times a minute. This would not apply to a booster fan since they're made to run with another fan

  6. fire hazard no telling when they quit but i know they do. You really need to access risk/gain, usually they are good for 5 months atleast but if you have a hps you should invest in a reliable and safe inline fan also like killset mentioned you may not get ideal cfm.
  7. The inline fan isn't a booster fan if this helps any, but I think that exhaust is more important?
  8. Do you have an inline fan (Grounded plug, sounds like a jet engine) or a booster fan ( has three wires sticking out & looks like a tin can) ...?
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  9. Its actually a a 7 inch room fan sealed to a duct. Its like 700 CFM
  10. What do you mean? Any pics of the fan?
  11. Its this fan with a short 8 inch duct sealed with duct tape.
  12. That's not an inline fan and won't even come close to 700 cfm. I actually have that fan. You need a real inline fan. My 440cfm inline fans blow my fan like that out of the water. Not even close.
  13. Would an inline booster fan work fine? If not could you point me in the right direction for a cheap inline fan?
  14. No they are boosters to work along side another main fan. Alone they don't even pull half the rated cfm. You need a better set up. Having the proper ventilation does more then help with temps. It also makes sure there's a steady supply of co2. You need a real inline of the right size in that size grow
  15. Could I possibly get away with only buying one of these. If I did have one would it be more important to use as intake or exhaust?
  16. #16 killset, Mar 27, 2016
    Last edited: Mar 27, 2016
    I take it you missed where I gave a formula to figure out the minimum fan size. It's something you may want to remember for future tent/fan purchases.

    4×4x7=112 cubic feet

    So you're tent is 112 cubic feet and the minimum recommended amount to turn a grow over with an online fan is 3x a minute. I do 5 because I like even more control and run multiple hoods in line.


    So the minimum cfm you would want to keep a steady supply of fresh co2 is 336. Now filters, bends, long duct runs create drag. So it's nice to go bigger. It's also nice to double that cfm and get a speed controller. This will do 2 things

    1 give you added control when needed

    2 a larger fan turned down is quite then a smaller fan on full blast

    Also remember....incoming temps are just as important as fan size. If you're already pulling in air in the mid 70s or more don't expect it to stay there with a heat source like a light no matter how strong the fan is. There really is no substitute for a quality in line fan. I've been burned by the cheap ones and had to rebuy better ones so I'll reserve my opinion on the brand of fan because I don't know your financial situation. Sometimes you gotta do what you gotta do. I stick to quality products and take whats proven to last, run quite, efficient so on and so forth, over price

    So 700 + a speed controller would be fine. You probably won't need you run it full blast.
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