sledge&wedge
ArboristSite Operative
You might consider going to smaller diameter pipe inside the barrel so that you have a bigger heat transfer surface to really suck the heat out.
Definitely a consideration to keep in mind. I thought about that initially, but I found a 6" duct-booster fan for cheap when I was ordering parts so I am going to start with that. However, I am planning to position the 6" tube dead center of the upper barrel so that I can go in and install some smaller tubes around it if I feel I need more heat. Thanks for the suggestion.