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How often to run exhaust fans - beginner?

Posted by growinsnow none (My Page) on
Wed, Jul 11, 12 at 18:20

Hey everyone - I'm new at hydroponics, and I'm setting up my first grow tent. My question is how often and for how long should I run the exhaust/intake fans? Everything I've found is geared to growrooms with HID lighting. I'm using a 300W 7-band LED grow light, and even with it running 24/7, with all vents to the growtent closed the temperature inside doesn't get above 79 degrees. With it off, the temp will drop to 68 at night. Is the purpose of the exhaust/intake fans mostly to drop high temps and humidity from HID lighting? Here's more info on my setup if that helps:

-DarkStreet Grow Tent 48"x48"x72"
-300W 7-band LED grow light (emits barely any heat)
-6" 240CFM exhaust and intake fan (2 fans)
-6" ducting
-Exhale CO2 bags for CO2 generation
*Grow tent is in a cement storage room in our basement, so temps stay pretty consistent.

Any help would be very much appreciated! Thanks!


Follow-Up Postings:

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RE: How often to run exhaust fans - beginner?

yes, normally exhaust fans are to remove excessive heat.
could be an oxygen / CO2 thing as well, but that isn't usually an issue.


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RE: How often to run exhaust fans - beginner?

LEDs are a joke. They work, but you might as well use spiral florescents, which give you more light for about 1/10th the cost if you build them yourself.

Your tent is 4x4x6= 96 cubic feet. Your exhaust blower moves that much air in 24 seconds. You'd be fine with a tiny computer fan instead of your big blower. I would just add more light, which would make more heat, and then you could put that blower to use.

And you don't need both an intake and an exhaust fan. One of them can be passive, which means just a hole. Air pressure will make fresh air find a way inside the tent if you are actively exhausting.

For most people, if you have access to fresh air at all, CO2 will be a waste of time. That CO2 generating bag thing would be most useful if you had everything sealed up in a closet and were not able to ventilate with fresh air. But it's tricky, because you don't know the CO2 level of the air without a meter ($500 US last I checked), and too much is bad.

If I were you, I would lose the CO2 bag, add more light, and run a smaller blower constantly to regulate temperature. Stanley makes a variable speed floor blower and sells it at Wal-Mart for $40. I think the 3 cfm settings are 90,120, and 250. Also, 4" ducting would be plenty, rather than the 6".


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RE: How often to run exhaust fans - beginner?

Everything Cole Robbie said is 100% true. Well said.


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