No worries, Freeburn! It's a lesson I'll never forget! So, assuming that I'd just threaded them by hand instead of cranking them in tight with a pipe wrench, they wouldn't have bonded and I could take it apart? That's good info and will be duly noted for the next version! The change in hole patterns was driven by some calculations I did. When I figured the mass of air needed to completely combust the volatile gasses from my average size fire, I just didn't think my 3/4 inch pipe and 1/16 inch drilled holes (about 36 in each upper burn tube) were giving the fire anything close to the needed air supply. On the other hand, I also calculated the BTU's needed to preheat that volume of air and the surface area of pipe required to transfer the heat to the moving air volume. Unless I want to put almost 13 feet of 1 inch pipe in my furnace, I'm just going to have to make due with a smaller air supply! My goal last night was to start working toward the happy middle ground between not enough air and too much air for my current system to sufficiently preheat. The holes were in a set of 3, staggered rows per tube, with 12 holes per row. The middle row is at 6 o'clock and the side rows are at about 4 and 8. I left the side rows at 1/16 inch and drilled the center holes out to 1/8. I also added a 1/8 inch hole to the tip of the end cap on each burn tube to try and supply some air to the gasses that sneak by the baffle without contacting the burn tube area. BTW, each burn tube is a 1/2 inch iron pipe, 12 inches in length. I immediately saw a dramatic increase the secondaries, a 75 degree increase in stove front temp and a 50 degree increase in flue gas compared to a nearly identical burn the night before. Actual burn time was identical. I'm now debating drilling out the side rows to 3/32. At the moment, it looks like the increase in volume was beneficial and didn't exceed the system's ability to preheat it sufficiently. If I increase the volume again, I risk reaching the point where the preheating isn't sufficient given the new increase in air mass needing heating. I'll burn with it as is for a few weeks before making a decision. I'll also try to remember to get some pics up tomorrow, including the burn tube patterns.