I don't know what to tell him. My buddy is going to install my Timberline in his totally unfinished basement( 1700 sq.ft.), totally open w/dirt floor. It's a modular built into a hillside, with concrete foundation on 3 sides, low side is stud framing. There will be no negative pressure issues, as the upper half is not connected to the basement yet, and he built in a barn door, so air flow will be gentle. His plans- Stove, 4' of vert. dbl. wall, 2- 45 degree's to a horizontal(about 24") through a thimble, to a "T". Verticle for 14' after that, leaves 3' above ridge line. Question is, since the 14' of exterior pipe will be on the cold, windward side, CAN it be necked down to 6", to keep the thermal velocity up? Or should it stay at 8" for the entire run? His plan is to run it at night only, which will give him a 10hr.(avg.) burn.