Just called my friend with the soap stone stoves— one is 12 years old and one is 16 years old. He burned the first one up fairly quickly. Something about you divert the air from the fire around the "cat’ until a certain temp, then you move the exhaust so that it goes to the “cat” and at the same time have to shut the air down to keep from getting flames up into the “cat”. He has to put in a new “cat” every two or three years, when he operates it properly. I don’t know if it is important to the soapstone stove or just good heating practice, but he has learned to clean the chimney annually.
I guess when it come to secondary air, I will have to let others work on it and when I see something I can copy, I will. My basic understanding isn’t good enough for experimenting. I had a heater made out of 2 - 55 gallon barrels, with one of the kits you buy. Over time, there is a 6 inch pipe about 4 inches long between the two barrels. It rusted out after time. I have wondered why the leaks in that pipe did not work as “secondary air”. TomC