Today's question comes from Brenda. "Hey Dan, I noticed 82% efficiency on the Lennox gas fired steam boiler. What does that mean exactly?" Well all boilers are rated according to AFUE, which mean annual fuel utilization efficiency. Like if you had a gallon of gas and it's 82% AFUE, then it means 82% of that fuel is going to get converted into heat, and the rest is going to be a waste byproduct. 82% isn't bad, but you can get higher on some new stuff, like 90% - 98% AFUE. You're never going to get to 100% AFUE. There is always going to be some waste byproduct, because thats just how combustion works. And it's a good gauge of efficiency.