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Need help with passive ventilation


New Member
I have a 4x4x5 veg tent temps are around 79-81f...I would like to get it down to 75 if possible! I need to know the best setup with my equipment for a passive system:
4x4x5 tent
400 watt mh
409 cfm sunleaves 6in inline fan
160 cfm 6in duct booster fanx2

I also have a 5x5x6 flower tent I need the same help with? my temps get 82 in there :(...
5x5x6 tent
1000 watt hps
728 CFM vortex 8 in inline fan
250 cfm 8 in duct booster fanx2



Well-Known Member
Where are you exhausting?

I used to have temp issues running 600w in a 2x4x5' tent, ran up to 85-90 sometimes 93. I recently got it down to 76 at canopy by adding a much larger hanging fan, extremely loud but she gets it done.


New Member
Cool the room cool the tent. You have more exhaust than is needed. Can you draw or explain how you have your tents rigged. My 4x8 tent is rigged as follows:

400 cfm fan attached to the wall flange. (fan inside tent). 18" outflow pipe vented directly outside. The 6' fan is ducted through 2 air cooled fixtures. The second fixture is my air intake for the exhaust system. On the opposite end from the fan my tent has 2 8" duct pass throughs. I put a 6" flex duct in each one and have it routed to the floor. These are my passive intakes. I closed off the flap intakes at the bottom as they leak too much light for my liking. With 2 600 watt bulbs going I can get anywhere from 5 to 15 degrees warmer in the tent than ambient. I control the heat with a good fan speed control. If I have heat or humidity problems I correct the room and that corrects the tent. My RH stays fine in the winter while in veg with out any help. In the summer I run a dehumidifier inside the room with the central air on and my plants stay happy.

What are you using the duct boosters for? They would probably be unnecessary unless you were venting a long way from your tent. Like half way across the house. And you don't say what kind of fixtures you have. Are they air cooled? If not that would probably be your answer. Good luck!


New Member
Air cooled hid lights are awesome. Like was said an explanation of how you are setup..or even some pics will help wonders to give you good information..
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