Well the 80 effeciency of the boiler is the burn chamber efficiency. Then convert that heat to the cast iron and lose some, then to the water and lose some, then to the pipe and lose some, then to the fin-tube and lose some then to the air and lose some...
Wood stove convert to cast iron and lose cast iron to air and lose some and done. I have a Jotul stove... Se the efficiency below... Not too far off the boiler.
Technical data for Jøtul F 600 Firelight CB
Maximum heat output: 81,500 BTU/hr
Heating capacity: Up to 2,500 sq.ft
Overall efficiency: 71%
Log length: 24"
Burn time: Up to 10 hours
Finish options: Blue/Black, Ivory, and Jøtul Iron™ Enamel, or Matte Black Paint
Flue outlet: Top, and rear
Flue size: 6"
Weight: 465 lbs
Accessories: Fire screen, Floor bracket kit, Bottom and rear heatshield
Jøtul has a policy of constant improvement and upgrading. Products therefore may differ in specification, design, material or dimensions at any time without prior notice.
Technical documentation for Jøtul F 600 Firelight C