EDIT: I mis-clicked and left out part of the burn data. Corrected efficiency is 56%. I changed numbers to match corrected data. Balance of post stands, but improved efficiency from dry wood in later posts is blown out of the water. Pretty sobering data. I ran a detailed analysis of the live burn that I did two nights ago. Worked out to 48% efficiency. Either I'm missing something big, or I have a lot of room for improvement. Here's how it came out: 94 lbs wood at average 30% moisture = 65.8 pounds 'bone' dry at 8600 BTU/lb = 565880 potential BTU Top floor: 94 minutes at 180 BTU/min = 11,700 BTU EDIT: 17010 Main floor: 93 minutes at 300 BTU/min = 15,900 BTU EDIT: 27750 Bottom floor: 71 minutes at 380 BTU/min = 7410 BTU EDIT: 26980 Hot Tub: 36 minutes at 586 BTU/min = 21,120 BTU Hot water: 47134 BTU -> 50979 BTU = 3845 BTU Storage: 81717 BTU -> 301817 BTU = 220,100 BTU Total delivered heat energy = 316,805 BTU Storage BTU is calculated as usable BTU, assuming that 120 degrees is the lowest usable temperature. In the storage tank, the top and bottom temperature probe covers the top and bottom quarter of the tank, while the middle covers the middle half. The hot water tank is 40 gallons. Hot tub heat load is based on the previously measured ability to raise the temperature of the 550 gallon hot tub by 8 degrees per hour. I've clearly lost some efficiency in that the EKO, refractory, steel, and water, is at 140 degrees when the circ shuts down. That heat energy is lost to these calculations, although some percentage of it ends up heating the basement as opposed to going up the stack. This was also a really short burn, with the house needing very little heat and the storage and hot water tanks not depleted at all. Am I missing something, or am I really only getting 56%? My wood consumption has been right exactly on track from previous seasons - a bit under two cords from October 15th until now.