Thanks Mike for the heads up about the rules of DIY. This newbie didnt know the rules. I am getting addicted to this site and certainly want to abide by the laws here.
As for the rafters, you guys really know your stuff. I googled heart checking and indeed it appears to be a common issue with these "vegetables" that we use to build our houses. There is nothing comforting about seeing cracks in the sticks that hold my roof up, but you make a great point that the engineers account for these flaws. The 2X12s were a bit of overkill anyway. Now back to finishing the stove venting. I promise not to get side tracked again.