Tell me more about how you measured efficiency. I think anything in the 80+% range is good, and obviously the higher the better. I have used two methods. Both methods use weighed wood burns and assume 20% moisture content and 400F average flue temperature, and with those assumptions wood has heat content of 6040 btu/lb of available energy
1) Conduct burn with the entire output going to storage, no other system demand, measure the increase in temperature of the storage over a period of time, calculate stored btu's. Not measured in this method is heat loss from the boiler itself, the plumbing and the storage tank. For my system the plumbing and the storage tank are both quite well insulated.
2) Conduct burn with known boiler gpm flow rate, log supply and return temperatures over time, and calculate btu output of the boiler over time. Not measured in this method is heat loss from the boiler itself.
Both of these methods measure heat captured to the system.
1) Conduct burn with the entire output going to storage, no other system demand, measure the increase in temperature of the storage over a period of time, calculate stored btu's. Not measured in this method is heat loss from the boiler itself, the plumbing and the storage tank. For my system the plumbing and the storage tank are both quite well insulated.
2) Conduct burn with known boiler gpm flow rate, log supply and return temperatures over time, and calculate btu output of the boiler over time. Not measured in this method is heat loss from the boiler itself.
Both of these methods measure heat captured to the system.