Difference in fuel consumption is obtained by dividing efficiency "after" by efficiency "before" or 74.39%/61.72%=1.205%, respectively. It follows the original boilers would have consumed 20.5% more fuel. In case of efficiency division the measurement uncertainty is canceled out for being the same in both cases (when a number is divided by that same number the result is 1). It follows the result is 100% accurate.

Unmatched performance. Lowest maintenance costs in business. More than 50% less area needed to generate same amount of steam by sub 2.5sq.ft./HP design.

Thermal Imaging - FLIR

Warga boiler: minimized exterior losses by all sides water-backed