I used to push the air through the fan and it worked OKAY. However I bought a cheap ducting fan, did a switcheroo, and have one fan pulling in cold air from outside into the grow box... and one 45-watt 6" ducting fan that's pulling the heat from the cool tube, and blowing it onto my clone dome in a different room. The other end of the cooltube connects to an exhaust for my box.
So right now in my grow box, I have one fan as an intake to the grow box, and one fan pulling from the only exhuast in my grow box... through the cool tube... all the way into an adjacent room where that fan is, and there is no other exhaust in my grow box. With that said, the cool tube is significantly cooler, can definitely touch it, and temps never exceed 75F...
again, with no exhuast for the grow room... i only installed one exhuast the cool tube is using it. Just make sure both ducting ends of the cool tube lead to outside of your flower/grow area. And I suppose pulling has worked out better for me, mainly because there's a source of cooler air to cross the bulb as oppose to my other grow room.
Here's a pic of my set up to get a better idea:
Cooltube pulling air to go that ---> way
You can see my intake fan pulling in cold air from the outside to the growroom (on the left), and the intake for the cool tube (to the right of that) leading to the top of the grow box.
(I used to use the intake for the grow room as my fan for the cooltube to push air out the top exhuast while intaking from the grow room, so sucking out the growroom air and exhuasting, didn't work out too well... needed to have both ends lead to different rooms) * Again no exhuast for the grow room because of this and temps will NEVER go above 75, I'm lucky, didn't have to drill any more holes
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