Now I just wanna know how you attached your humidifier to it!
The humidifier intersects the incoming air duct before it reaches the terrarium:
Just remove the directional flow cap out of the humidifiers output hole on the top of the tank. It's used to aim the fog where you want it in the room you won't need this. It pulls out for cleaning on most models I've seen. Then just stick a 1 1/2 - 2" diameter sump pump hose in the open hole (the hole is 2") and duct tape it in place. Then cut a hole in the 4" duct and stick the loose end of the sump hose in there and duct tape that in place. Turn the humidifier on and watch for any escaping fog vapors put more tape where there are leaks and then you're all set to hook up to a controller.
Note: I used to use clear tubing to go from the humidifier into the duct but it's rather expensive and algae actually grows in the clear tubes eventually blocking the airflow. The black sump hose should not have any algae grow in it and I got 25 feet of it for like $6. I only need 12" or so for this project.
Oh, the humanity!!
That's interesting... thanks for posting! Having just done something like this myself, I had problems getting my fan to force all its air flow down the duct even though it was a 4" fan and a 4" duct. Do you feel like you get all 85 CFM out of the other side of your duct?
I just bought myself a duct fan - it's rated for 50dB. The Radioshack fan I have is rated at 36dB. Hmm. I hope it isn't too loud... that would be a real bummer. I might have to switch my fans for something more like yours...
And the 12VDC fan - I actually have that same Radioshack fan but the AC model that puts out 60CFM. Is there an advantage of DC over AC besides the apparent difference in air flow?
Any bends in the duct will reduce your flow by an exponential amount, the straighter the duct work the better for air flow. You wouldn't actually want 85 CFM blasting full bore into the terrarium as it would dissipate the humidity very rapidly, as long as there is a slight breeze keeping the air moving it's enough to keep it cool.
This is how I had the duct setup on my old 3 level succulent shelf (note no humidifier) using two 4" Ts and 1 90* elbow at the top to deliver airflow to each shelf.
I used to use the AC fan from Radio Shack but I like the DC ones now because of the switchable power supply which gives you more or less air flow and reduces the volume if the top setting is too loud. I sleep in the same room as my terrariums so I couldn't use the 4" diameter Inductor duct fan. I bought one and wired it up but it sounded like a rattling jet flying outside the window. I knew I couldn't sleep with that going 24/7. There may be a way to quietly mount them to something and if you don't sleep in the room it may not matter either if you can go out and shut the door. At the hydroponics shop they sell a fancy high power and quiet fan (at least how they have it mounted it's quiet) but they want over $100 for it and at the speed it runs it would likely eliminate the humidity I'm trying to build up in there.