OK, I just tested in latest dev.
Out on the street, one charcoal, one 2x4, and 7 whiskey burned HOT and for well over 100 minutes. (I know because I had enough time to build a stone fireplace (40 min.), light the same fire in it, and wait two halves of an hour afterward.) The fireplace fire stayed Small, rather than Raging as the open fire did, but I think an hour with no sign of damage to the wood & coal is enough to get some use out of the fire.
Sorry, xpyder.