There is no comparison to coal vs. wood in a hand-fired boiler. Wood provides short fires...try to burn it clean and the boiler overheats, try to control the fire and it produces creosote. My Itasca boiler would hold a considerable amount of wood, and if I was lucky it would still have a bed of coals in the morning. When I used to reload it in the morning it would really roar to get the house back up to temperature! The smoke & vapor plume above the chimney was impressive, but hardly a sign of efficiency.
Nut coal was a different story, the boiler kept the house toasty overnight on all but the below zero days, and after a few days the creosote in the boiler and chimney started to flake off. There is still nothing better than a stoker, but anthracite in a hand-fed boiler is a good way to split the difference.