Help with Fans & Venting Needed PLz - New to Growing

Discussion in 'Grow Room Design/Setup' started by newtogrowing, May 24, 2010.

  1. Hi Guys,

    I am in the process of assembling my first grow tent, and attempting to grow my first batch... Im intending for this grow to be 'experimental' so I can learn, and make adjustments based on results, etc... BUT, for now, I am hoping someone may be able to help me out with a few specific things here... Have had a look throughout the forums, and found a few guides here & there which assist, but was hoping, if I could give you my specifications, someone here may be able to give me the best advice & recommendations, to suit my design & requirements... Anyway, here goes...

    I am hoping to keep this grow as stealthy & inexpensive as possible, but it doesnt have to be completely so...

    I have bought a 90cm x 45cm x 180cm grow tent (3' x 1.5' x 6'); black exterior, mylar interior. Now, in this tent, I am going to be hanging a 250w HPS from the ceiling. The tent has 2 air holes; one is for exhaust at the top right corner of the tent. The other is for intake at the bottom left corner of the tent.... Both of these holes can be adjusted to hold 100-200mm fans (one for intake, one for exhaust, obviously)...

    I am only gonna be growing 2 or 3 small plants in here, to start off with, mainly so I can get the hang of it all, n whatnot...

    Now, what I am hoping for help with....

    The tent will sit in the corner of my bedroom, next to an open window (hence the, not completely stealthy thing) on the 2nd floor of my house.

    Now, my questions come (primarily) in relation to airflow & ventilation, and the positioning of the fans...

    Given that I am using a 250W HPS in this size space, how hot is it likely to get? How much is it likely to increase the tent temperature??? Currently, during the day, my indoor temps are probably around 18-25 degrees C (64-77 degrees F) and a bit lower, during the night....

    What I was hoping/intending to do is, install a small Ezi Air inline fan at the top hole, for exhaust - only 100mm 21W... I wanted to leave the intake hole open, but only use passive intake, as opposed to a fan for intake (this is where the budget comes into it all)... Do you think this would be enough? And would succeed in creating sufficient airflow/ventilation???

    Given the temperatures here, my plan was to set EVERYTHING (lights AND fans) on the same 18/6 timer... So everything will come on at 4pm, and run the whole way through, till 10am... This way, during the coldest part of the day & night, the light will be on, and when its warmest during the day, everything will remain off... Im thinking, by turning the fans off with the light, as the temps are a little lower than ideal, having the exhaust fan off while the light is off will help maintain the temps a bit more, keeping some of the heat from the lamp, before it cools.. (?) and that way, by not creating negative pressure, I wont be sucking in as much fresh air during the day, so it wont cause too great a drop in temperature, when lights are off.... Does this make sense to you all? Does it sound achievable, and suitable for my sort of setup??? This is my primary concern....

    Next, still on fans, comes the airflow & circulation, within the grow tent... How can I achieve this? Again, given the size of my tent, and size/power of my lamp, do you think merely having the exhaust fan installed & operating with the passive intake, at opposite corners of the tent will ALSO ensure there is sufficient air circulation within the tent itself???

    The only oscillating fans I can find are (smallest) 30cm diameter... Given the length of my tent is only 90cm, wont this be a bit too big??? From what I have gathered, it is fairly crucial that I have an oscillating fan in there, to make sure the stems get strong & air is circulated... So are there any other ways I could achieve this??? And if I have to get an oscillating fan, should I aim it directly at the plants themselves, so the entire plant gets blown with (light) air, as it moves back n forth??? If I were to do this, using my 250w light, will I still need to get another fan between the light & canopy, to blow the heat away? Or do you think a 250W wont put out enough heat for it to really be a concern???

    Primarily, I am really looking for help in regards to where I should position the fans to ensure maximum airflow, ventilation & circulation within the tent, whilst maintaining a decent temperature... And oscillating or not... I just know, unless I can find a smaller oscillating fan (which I cant) its gonna be a major struggle to fit it in my tent... As a last resort, could I hang it from the ceiling, by chain??? And the turn it on once it is just hanging there, to blow back & forth??? I thought it'd be best to position the fan blades in line with the plants, so the air is blown directly onto them, as the fan oscillates, but if someone disagrees, or has a better suggestion, PLEASE let me know... Could it be placed in a top corner of the tent, on a higher setting, so it would blow down, across the tops of the plants, or will this not work as well?

    At what height should I be hanging a 250W HPS, above the plant tops? I know about testing it with ur hand and all, but just wanted to see if anyone had any experience with these, to suggest something... I was thinking roughly 8inches, but wanted to hear what everyone else thinks...

    And finally.... The ventilation.... My room is probably about 4.5m x 3m x 2.5m or 15' x 10' x 8' (very rough).... The tent will be in the corner of the room, away from the door, with the door closed... Window is directly next to the tent and open, all the time...

    Could I just use the exhaust fan to blow the air out of the tent, directly into my room (ie, with no ducting) and still have the passive intake coming through the bottom... As the window is always open, there is bound to be enough fresh air coming in, and the exhaust air will be able to get out the same way.... Am I right in thinking that??? Or, do you think I will need ducting, to aim the exhaust air to blow out the window, at the flyscreen???

    And finally, on that - how bad is it likely to smell if I were to do it this way??? If im blowing the exhaust & 'fumes' out the 2nd storey window, is the smell going to linger as bad as it would if it sat at ground level...? Im mainly thinking in relation to neighbours, etc??? Is it likely to reek them out, or probably not so much, as it is smaller, and the hot air will rise, hopefully taking some of the smell with it...???

    I know Ive gone on for a bit, but am hoping someone can suggest something, based on my specifications, and all ur knowledge & expertise... Any help would be much appreciated...

  2. ... Anyone...?
  3. I haven't been getting a lot of help in this fourm either. But if I was u I'd buy a 250 cfm inline fan from hid hut
    And a carbon filter. If your light has a hood vent thru room hood filter fan. That way you get rid of heat and smell. Just leave the intake
    Hole open. It will suck air with the fan.
  4. You know, I've been growing for several years, and have been in the heating and air conditioning biz for about 10 yrs. Your questions are quite valid, and I would be concerned just as you are. A 250W HPS will generate approx 1000 BTUs of heat. That is not all that much if you were in a LARGE room, such as a garage or similar, but your room is your tent, and it is not very big. My suggestion to you would be to set it up the way you want and turn it on overnight and see what your temps are. Depending on your temps you might be able to get away with just an exhaust fan and have incoming air passively .... but you will need to enlargen the intake hole at least 2 or 3 times its size.

    If that doesn't work, and its still too hot, you will want to determine the outside air temp vs the inside temp in the room, and bring in air to the tent the air that is colder by venting it coming in straight from the source. You will need a fan that will bring that air in, it will not be passive.

    Again, I would say set it up without plants in it, and see what temps you get. You might also consider running the light during the night as the ambient temps are lower at that time than at high noon.


  5. Those inline fans are not ment to pull air thru a carbon scrubber(they are designed for a straight pipe to boost the air flow further away from main unit). Spend a little more and get a inline/cage fan.
  6. Arent inline cage fans less legit then a inline exhaust fan? They say on there website what kind if carbon filter you can use with them
  7. What kind of fan are you talking about?

    I thought you were talking about this kind....

    those would be the kind I would stay away from.

    I run this kind in my rooms and have no issues with them at all...Grow room ventilation - squirrel cage fans, whisper fans - - Vortex Powerfans 6" Inline Fan- 450CFM

    Cage are not my choice...but would not choose the first for anything other than maybe bringing in fresh air.

    If I was mistaken on the fan you were talking about sorry about that.

  8. yea i was talking about a inline high output fan, not one of those. like a vortex type
  9. ah sorry about that...just misunderstood

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