I'm not a good mathematician, but I can decipher those numbers for you: 25,000,000 btu's available per cord of good hardwood, not even the very best. Something like white oak, mulberry. divided by cubic feet per cord (128) multiplied by cubic feet the firebox holds (3.75) multiplied by the efficiency of the stove (.8) divided by hours burned (17) Looks about right to me Solar. My old Royal Heir seems to be holding up to the numbers I cranked after buying, before running. People that have not run a cat stove with thermostatic air control just refuse to believe the results. It is not magic, they cannot put out more btu's than the wood can give, but it is a very controlled burn, and very little heat goes up the chimney, with very little fuss over running the stove. I'm anxious to see how my stove holds up under colder weather to see if it still will handle our heating needs, and distribute that heat as well as it has in the shoulder season.