I have not really been following this thread so I don't know all the details of the problem, but it sounds like you are not happy with the wood consumption of your system and are trying to figure out where all the btu's are going, correct? I also am not sure if this has been suggested yet, sorry if it has. What I did was isolate my underground pipe where it enters the house. It takes 3 valves and 1 loop, similar to the bypass of a water softener. Then get a 5 gallon bucket and pull the return pipe off the owb and catch the water for 20 seconds. Measure and multiply by 3, you now know your gpm through just the underground pipe. Build a small fire to get your boiler up to high set point then turn off the fan, noting what time it is. Let the circulator loop through only the boiler and underground line, the longer the better but at least 4 hours. At that point check the water temp at boiler and figure btu loss. It is a pain in the neck but it will tell you if there is a problem with the underground line set. No more guessing.