That is good details there John and yes I do remember early coal fired boiler / warm air furance those unit were huge and I did work on one steam boiler { 15 PSIG system } it took a while to get the steam up but once you got there it stay there for very long time and it last pretty long time before have to refired again.
Those common resdentail / light commercal- industrail burners you can able change the firing rate { size } by changing the nozzle size and adjust the air door a little.
Yeah they can burn almost any fuel it go thru but not gasoline { too fast for combustion chamber } they can burn #1, #2 Diesel fuel / Heating fuel , Keronse , Jet fuel , some case old engine lube oil { if preheated yeah it will burn pretty good }.
Merci,Marc
