I'm in the process of rigging up some air under fire in my barrel evaporator. Would like to plumb the air in from the back of the barrel via some 4" flex duct and a variable speed duct fan, and then with some 2" black iron pipe (1.5" ID, about 3.5 feet or so) into the barrel, and that pipe will have a bunch of holes drilled into it. Any thoughts or concerns whether that 1.5" line will be able to deliver enough air to run as hot as I'd like? Could probably go to 2.5" if I needed to, but 3" feels like overkill.