Some crack for the graph addicts..... I finally got my thermocouples installed. I didn't get them in until part way into the fire, but it's better than nothing. The first one is in the secondary combustion chamber. It's near the outer wall, and shielded from the actual combustion by a baffle. Combustion gases have traveled through my labyrinth before they get to it. The second is in the flue, just outside the boiler, about 3" past the bypass damper. I calibrated them as best I could. I wrapped them both together with a calibrated thermocouple and stuck them in the combustion gas path at about 900 degrees. I then calculated the gain and offset values required so that my readings matched the calibrated unit at room temp and at 900 degrees. In the graph, the thermocouples are the two lower analog signals. Multiply the readings by 10 - that would give you a peak secondary combustion chamber temp of just under 1200 degrees, for instance. The digital I/O is as follows, top to bottom: - Baseboard demand. Introduces cold water, as you can see towards the right side - Wood boiler recirc valve. Opens to keep inlet temp above 140. - Tank zone valve. Opens to dump heat to tank - Hot tub zone valve I was surprised by a few things. The flue temp was WAY higher than I expected. I have a magnetic flue thermometer about 3' downstream from the thermocouple, and it never broke 300 degrees during the fire. The dips in the flue and secondary temps are from the EKO controller idling momentarily as water jacket temps reach 80 C. I plan on doing enough burns to get a good baseline, then tinkering. I might even try something as radical as cleaning the HX tubes! One problem, though: the temperatures in the secondary chamber vary wildly from spot to spot, and I can't be sure that any changes in secondary temps are due to anything more than changing the flow pattrens so that the probe is in a hotter or cooler spot. I'm interested in any thoughts, insights, questions, or analysis. Does this all make sense? Does this suggest that there are things I could / should be doing differently?