The BTU mod adds a high fire max time and a new auger timer, so you end up with a max high fire timer, a high fire burn rate(BTU) timer and a low fire timer. Plus you change the auger motors to I think 4 and 2 rpm from 2 and 4 rpm (from memory on the rpms, but you get the idea) Sounds confusing, but you end up with a separate control for high and low fire and still thermostatically controled. The high fire max time is so to keep you from going full out all the time. I put a new aluminum feed tube on this fall and now it feeds too much corn for my air settings. The PVC tubes must really restrict the corn flow. The BTUs are infinitely adjustable now with in range, though they print up a chart showing 80K, 90K,100K, 132K and 165K BTU settings. The only time the low fire timer comes into play is very early and very late in the year and even then I can turn the high fire timer to below 80K and the low fire to 1min and 12min. But this all assumes that I'm home to do it all. The windows get opened a lot when I'm not around during these times. I have never went beyond what I calculate to be 115 to 120K BTU, that was a few years ago, breezy and -35F. This year I went to 100K for a couple of days, but I have no idea what my new flow rate is. I'll have to check it out when it gets warm, so that I have it nailed down for next year.
