yeap did that one time once when the heater was down for the count kept the kitchen warm enough but had to use space heater as well to unfreeze pipes in bathroom. Pretty good hack for sure that is essentially what your gas furnace does heats up a metal/ceramic element and then air is forced around it through it etc to provide heat ;)
I still think the jail boxes they used on the southern side of their homes was more interesting they were huge clay fired black boxes they would place on their south facing wall and they would open up vents during the day to let the warm air in from the sun manually.