I ran a little experiment on one of my BK Ashfords last night. Learned / confirmed I could only expect about 24 hours active cat on a short 15 chimney when the temperature was > 50F outside on a 4-year old combustor, which is still miles beyond any other similar size stove on the market, but short of what it can do with good draft in January.
The experiment was run with only a 75% wood load, as it was 50F outside and this 3 cu.ft. stove is only heating something like 1200 sq.ft., depending on how you count it. So, when I say "24 hours for a full load", I mean I measured 18 hours on a 75% load of wood.
I initially pushed for a longer burn, turning the dial below my usual 24 hour setting, and using
only 25% of a full load in 10 hours. Impressive, but the warm weather, short chimney, and 4-year old combustor were all conspiring to push me toward a cat stall, so I increased the air at the 10 hour mark. You will see this reflected in the 100F jump in cat temp at that point in the graph.
Summary point 1: I think my combustor is doing fine after 4 years, now into its 5th season, and after roughly 12 cords.
Summary point 2: You need to have an ideal setup to push toward 30 hours... and 15 feet of pipe at 50F outdoor temperature is
not ideal. But hitting 24 hours is easy, even under poor conditions.
In the future, I'll try the same on my other stove, which sets under 30 feet of insulated pipe and is straddling a cat with more than 30 cords on it over the last 4+ years. I may also repeat the above on the short pipe stove, but in colder weather, seeing if this old cat can still hit the 30 - 36 hour times it did when new.