Thanks for the link! I went ahead and bought the pipe kit plus the concentric kit and a 45 degree kit. Might as well do it right.
Worked out to be cheaper to get everything through ACF Greenhouses than Menard's, even with their 11% rebate going on now. Looks like ACF has free shipping on...
Same thing here. Bought the 45K unit tonight, and am shocked at how difficult it is to source the items for the horizontal venting (and the price for Cat III / Stainless).
I plan to do woodworking in the 3 car garage so the 4" combustion air inlet kit is in my future, though I do not know...