Reason I ask is because I have the double wall pipe (heat-n-glo SL pipe) and I actually had a layer of ice in between the walls of the pipe last year up on the top of the pipe. On warm days or when you fired up the fireplace, it would melt and the water would run down in the walls of the pipe onto the fireplace. Not cool!
Anyway, I am not sure if this was from all the condensation going up the pipe (put it in our new house while they were sheetrocking upstairs) or if it is a characteristic of the metal pipes... Maybe the triplewall is better?
there are 2 pipes. one is a fiberglass filled and i'am not sure what the other one is. but one gets wet like you are reffering too.