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Thread: Exhaust Vs Intake

  1. #1
    bobhead is offline Registered+
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    Smile Exhaust Vs Intake

    Hi, I would greatly appreciate some advice.


    I have enough money to buy an inline fan. I have a small grow tent (4x2x6).
    Is it better to exhaust my 400w HPS or Intake cold air. My room can stay cold with my AC unit.

    Also, if I exhaust, should I intake the heat right next to the light.
    I read that in-taking the heat can burn out the fan, and that air should be blown through the light. But my light reflector will not allow that.

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  3. #2
    Ocotillo is offline Registered+
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    The customary method, in this case, would be to suck the air from the light and blow it out of the tent. An intake hole at the bottom of the tent is usually enough with no "intake fan". This is passive intake and works if your exhaust fan has decent CFM flow. YMMV.

  4. #3
    neceros's Avatar
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    I agree with Ocotillo. Air pressure will ensure that new air is brought in once you exhaust spent air.

  5. #4
    bobhead is offline Registered+
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    Thanks for the response.
    I think I will buy a 6" 400CFM fan.


    Instead of mounting it right next to the lights, I was thinking about placing it on the outside of my tent. Do you think 400CFM would have enough power to exhaust my tent?

  6. #5
    neceros's Avatar
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    Well, 400CFM means 400 cubic feet per minute, which even more simply put means it will take a minute to move 400 cubic feet of air. You said you have about 600. Personally, this should work for MY needs, but I don't know if it'll be enough for you.

    Trial and error.

  7. #6
    bobhead is offline Registered+
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    I see. Perhaps I shall add some inline duct fans for intake. Would that be better than having passive intake.

    I have oscillating fans as well; will the circulating air affect the efficiency of the exhaust?

    I did read the first thread about blowing hot air by the way; I'm still a bit confused. Anyone care to elaborate on static air pressure?

  8. #7
    Ocotillo is offline Registered+
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    So, you have 480 cf volume tent plus an air conditioner. I think you will be doing great (unless your in a 120f degree garage) and you could always add an intake fan if needed.

    About pushing rather than pulling the hot air.... Like our friend Rusty said, pushing the hot air will allow hot air to leak through hood seems and hose connections if you have any leaks. Your hood seems to have only one duct so you can't really push it through anyway so it's a moot point. You don't have to put the fan right at the hood. Your preferred method (fan to duct, into tent, to hood) sounds good. Anyway, you could, and may want to make adjustments along the way. I'd figure on that.

    There is a theory about the heat from the bulb will cause your fan to burn out, melt, explode, catch fire, insert disaster dujour here ___________. I say BULL! You have a 400W bulb, it'll be no problem. Even with a 1,000W bulb the duct barely gets luke warm to the touch. I think that theory is over thought and scary urban legend.

  9. #8
    bobhead is offline Registered+
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    Ah I see. I think I'll use some 6 inch hoses then. Of course this will limit its suction capabilities?

    I'm just gonna have to wait and see how powerful the fan actually is.

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