Marty S said:
Measuring 'stove top' or flue temps just above the stove are meaningless to determine this since the critical stack temperature for creosote formation is many feet away. Of course, if one is way off base and burns wood only by 'smoldering', creosote will form in the chimney closer to the stove and maybe there too.
I'm in 100% agreement about the meaninglessness of stove top temps to monitor the burn inside the firebox. But while I understand what you are saying about flue temps, I disagree that they are meaningless. We need some indicator to give us feed back about the quality of the burn, and the only way I can think of doing that is to monitor flue gas temps. IMO, the hotter the better (up to about 1000ºF). Hot gases rise faster in the flue, and velocity is the name of the game. Cool flue gases linger in the flue long enough to collect on the walls which is the problem. Fast rising gases improve the draft as well, providing hotter temps and more complete combustion inside the box, particularly in the burn zone. When the draft in the flue is improved, the air can be cut down which will increase the velocity of the intake air, giving you a livelier and more energetic burn. This is the principle behind a forge blower, where as more air is delivered faster to the coals, temperatures inside the fire itself rise dramatically.
Here's a composite photo I took last year of my old stove during a starting burn using three progressively smaller intakes air openings, each one 1/2 of the one before. No flue pipe temperature data because I din't use a flue thermo back then, but all I can say is that the stove was warm to the touch when I began and the flue pipe was scathingly hot before I started to reduce the air. Each time I halved the air, you could hear the stove accelerate and see the temperature inside the burn zone increase by the change in color. At 1/8 air, the coals inside were yellow-white... well over 2000ºF. Unfortunately, the fire was so bright that I had to make adjustments in the exposure to prevent it from blowing out the photo, so you really can't see what it looked like in person.
If I were to use stove top temps at the time I took the photos (taken about five minutes apart) at that particular time to monitor the burn, I would have predicted it would have been making massive amounts of creosote, but that was how I ran that stove with thin splits and dry wood, and there was never a trace of creosote in the flue anywhere near the stove. I'll guess that stove top temps eventually rose to about 700-800ºF within about 1/2 an hour from then.
This is the first time I've posted a photo on this site, so I hope it shows up. And don't beat me up about the condition of my poor little Jotul clone. It was a great little heater that cost me nothing but some stove cement, a couple of feet of gasket rope and a few hours work on a buddy's guitar. It saved me about $50,000 in electric heat over 18 years of 24/7 burning from Nov-Apr each season, and ate about 80-90 full cords of wood without complaing too much until the very end. And while it looks like it is leaking air badly around the joints, it was still quite air-tight, and shutting the air down completely in that stove would snuff the fire right out.