Do I need a separate exhaust fan

[JohnnyRotten840]

Hey all! I'm doing my first grow and am utilizing my a 3 by 3 by 6 foot grow tent with a 600 watt hps light.

The light is a sealed air cooled with a 220 cfm fan

I have a intake fan at 110 cfm but currently no exhaust fans, I have just been letting one of the 10" holes stay open.

Is it necessary to add an exhaust fan? My temperatures are a constant 82 during the light and 78 without the light. The intake runs non stop and the fan on the light is on a timer with the light.

My plants look fine, but at 2 weeks old they are only about 8" tall. I had some ph issues I just fixed about 6 days ago, and just started a good nutrient feeding (half recommended dose to start) so I'm hoping that this lack of exhaust fan isn't conributing

Thanks for. Any help!

 

[Dwight Monk]

If you going to only have one or the other I would think a passive intake would be better than a passive exhaust. I force air out of my shed (exhaust fan pulls air thru a carbon filter canister) but it just intakes thru a carbon filter mesh (like a prefilter on air filter) passively like a vent does.

 

[Crane]

8 inches is plenty for two week old seedlings. It's not so much about lenght but lush growth and closely spaced leaf nodes.

And I also concur that an exhaust fan is better if you only have one. Imagine it as drawing hot air out of you grow space but at the same time it's also drawing cool fresh air in through your intake opening. Those temps you mention sound pretty low for a 600W grow, is the air cold outside the grow space? Or is the fan from the air cooled lamp hood routed out from the grow tent? That would function as an extraction fan surely.

 

[JohnnyRotten840]

8 inches is plenty for two week old seedlings. It's not so much about lenght but lush growth and closely spaced leaf nodes.

And I also concur that an exhaust fan is better if you only have one. Imagine it as drawing hot air out of you grow space but at the same time it's also drawing cool fresh air in through your intake opening. Those temps you mention sound pretty low for a 600W grow, is the air cold outside the grow space? Or is the fan from the air cooled lamp hood routed out from the grow tent? That would function as an extraction fan surely.

The fan from the grow light exits outside the grow tent and into a large empty space. The room the tent is in is kept at 70 degrees

 

[Crane]

Oh yes then the lamp fan is your exhaust fan. It's sucking air out the whole tent, just doing it through the lamp hood. Those sound like really optimal temps.