been burning exclusively black locust for the last week and i can definitively say that the coaling is significantly less than sugar maple. was mixing the two or burning just the maple and was having serious coal buildup at the end of the day. i like a constant house temp and don't accept a 10 degree variation between loads like many on here. don't see in the directions for eng. 30 where you let the load burn down to nothing to reload, this 6 or 8 or 10 hour reload is a bunch of crap, i've got 3100 sq ft to heat. i feed it at least every hour