I am strongly considering installing a homemade outside air kit for my NC30 in my basement. It will be somewhat of a challenge since I would estimate about a 16' run with several bends. I also will have to core through a foundation wall in 2 different places. I have a suspended concrete porch with an interior concrete wall in the basement. I plan to run the pipe through the first concrete wall and into the storage room and then take it up just above grade and go through the concrete wall again. I do have access to HD hammer drills at work that could put a 2" or 4" hole in the concrete. I believe the NC30 has a 3" intake pipe coming out of the bottom. Here is my first dumb question. What if I tried to reduce this 3" pipe down to 2" or actually 1-1/2" since it has to make it through the hole? I hear that drilling a 2" hole in concrete is a lot easier because it significan't reduces the chances of hitting rebar with the core bit. I would have to think this would reduce the air flow. What do you think? If it is really going to hurt my air flow then I will go with a 4" hole & a 3" pipe. My reasons for wanting an OAK. 1. I just like the theory of pulling cold air from the outside vs warm air inside 2. Occassionally I have had smoke billowing into the room due to a negative pressure situation 3. I often in the off season get that foul & moist soot smell...particularly when it rains or when I run the attic fan. I would appreciate any of your thoughts on my plans to do this and in particular about the pipe sizing question. (Below is a crude diagram of the install)