Why did you do this?
Seemed like a good idea at the time, and I had nothing better to do that afternoon. I already had the smoke machine, and I wanted a nice ground-hugging fog for Halloween. To get the type of fog I wanted (about ankle deep), I needed to cool the smoke as it came out of the machine. I looked around online for inspiration, and ended up basically ripping off Allen's design.
You will need a moderately sized trash can, and about 20 feet of aluminum dryer exhaust duct. Now, I know that dosn't look like 20', but trust me, it is. Those little 3' pieces each stretch out to about 8' long. As for the trash can, I just found one that I liked. Round helps. You will also need some metal duct tape (not duck tape).Oh yeah. You'll also need a smoke source (duh!). I ordered mine online for about $30. Pretty basic: you put fog juice in the top, push the button, and smoke comes out.
Only one really. You'll need a jigsaw, or some other type of saw capable of making a round hole. A large hole-saw would work well, but I already had a jigsaw. A pair of tin snips is also nice. If you don't have some, you should go to the hardware store and get some. They can cut almost anything.
First, figure out where you want the holes. You'll probably want one on each side of the trash can. I just held the duct up and traced around it with a permanent marker.
I found it useful to drill a starter hole so I had a place to begin cutting with the jigsaw. You don't have to, but I would recommend it.
Now, stick the jigsaw in the starter hole and just follow the line. Pretty straightforward. Don't even know why I bother to mention it.
Next, you have to join the duct pieces together. I did this by cutting a slot in the end of one piece, stretching it over another, and taping it all up. It worked out just fine for me. When I was buying all the parts though, I saw that they had little aluminum joiner rings. If you want a slightly more professional joint, get a couple of those and attach them with pop rivets or screws.
Now, cram it all into the trash can. Feed one end through one of your holes, then spiral the duct around inside the trash can. When you're about out of duct , feed the remaining end down through the middle and out the other hole.
Testing and Aftermath
All that's left to do now is test it. I ran the initial test without any ice. When you want to produce a good shallow fog, pour about 25 pounds of ice into the garbage can with the duct work.