We are in the process of constructing a new home in a climate that now supports below 0 celcius daytime temperatures. I have installed a couple of electrical boxes on exterior walls of the second floor of our house. The electrical boxes have 3/4" EMT conduit leading up to the attic. The boxes and conduit are to be used for cat 5e and RJ-6 cable. Now that the insulation, vapour barrier and drywall is done and the house is being heated I seem to have condensation forming on the inside of the conduit. The condensed water then makes it way down to the box. I am now thinking that I should seal the bottom of the conduit as it enters the box and seal the top of the conduit in the attic to prevent air leakage and condensation. Any comments?