lighting question

Discussion in 'First Time Marijuana Growers' started by greennewb, May 7, 2011.

  1. #1 greennewb, May 7, 2011
    is a 250 watt hps light decent enough for a grow area that is 2'5" long x 1'6" wide x 4'7" high? probably only growing two plants in it.

    my grow area is a cabinet. will it be necessary to have an exhaust for this size of area and light mentioned or is it good enough that the door will be open the majority of time during lights on times?

    thanks.
     
  2. #2 420patient, May 7, 2011
    As long as you got good ventilation and can keep it cool your good 2 plants max tho.
     
  3. #3 greennewb, May 7, 2011
    thanks. i am assuming that you are saying that i don't need to include an exhaust then.

    EDIT: and i will most likely be using at least two extra cfls as well just for some extra coverage.
     
  4. #4 PizzaPalace, May 7, 2011

    You will most likely need some good exhaust fan.
     
  5. #5 fyrhazzrd, May 7, 2011
    As small as your area is you can probably get away with a 4" vortek exhaust fan.
     
  6. #6 greennewb, May 8, 2011
    thanks. i was thinking about getting a 4" PC fan.
     
  7. #7 fyrhazzrd, May 8, 2011
    a 4" PC fan may not move enough air to keep it cool. It's worth a shot though.

    You will need something that is rated at about 26.5 CFM to properly ventilate your space. If it were me, I would use a booster fan that they sell at Home Depot. They run about $30 and are rated around 60 CFM, but usually run about half that in reality.
     
  8. #8 greennewb, May 8, 2011
    PC fan not good enough? is it normal for fans to run lower than what their CFM is stated as? i was looking up some PC fans and even the cheapest ones were 26 CFM or higher.

    thanks for the help :)
     
  9. #9 fyrhazzrd, May 8, 2011
    I never really looked at PC fans to see what they're rated at I just assumed they were around 10 CFM or so.

    I don't know from experience about the booster fans at HD, I'm just going by what people here on the forum have said. They may hold their CFM rating, but I don't know for a fact if they do or not.
     
  10. #10 gho0ost, May 8, 2011
    pc fan is gonna be good for a small box like a pc case lol. you need something bigger. booster fan at least. with ventilation its always better to have more cfm than not enough.
     
  11. #11 greennewb, May 8, 2011
    found this formula online today. does this sound accurate?

    Q = V x P x C x dT
    where
    Q = amount of light in kW
    V = volume of air being ventilated in m3/s (m3/s = CFM / 2119)
    P = density of air (assume 1.2 kg/m3)
    C = specific heat capacity of air (assume 1.02 kJ/kgK)
    dT = temperature difference between ambient and grow space air in degC (assume 26 degC is best temp; and room temp is 21)

    therefore, in my case:
    V = Q / (P x C x dT)
    V = 0.25 / (1.2 x 1.02 x 5)
    V = 0.041 or about 86 CFM

    this seems a little high for my basic needs i think.
     
  12. #12 greennewb, May 9, 2011
    just found another source that states the following:

    "Your fan should be big enough to move the volume of your area 2 to 3 times every minute. A 70 CFM fan would be adequate for a 35 cubic foot area, and would be optimal for roughly a 23 cubic foot area."

    my grow area is around 16.6 cubic feet, so does that mean a 50+ CFM fan is optimal?
     

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