Probably old hicks and rednecks

I'd prefer coal or wood. Both cost much less and can be obtained for free in some cases. I don't use it, unfortunately. I rent and have no choice.

Probably millions...in poorer nations. Coal furnaces in the U.S. have been modernized (they had to be to meet home air safety regulations), and so they are very efficient and RELATIVELY clean compared to the former commonplace coal-burning furnaces and heating stoves. Also: they are few and far between in the U.S. I knew a co-worker who bought a house with a (relatively) new coal-powered furnace, and he was excited about it at first, but after one Winter he and his wife learned to HATE it and replaced it with a wood-burner. The main problem: the coal dust, which they could not stop from tracking EVERYwhere in the house every time they re-coaled the furnace. *** But you can imagine that there are many nations with cold winters that have ready access to coalbut do NOT have access to reliable electricity or to natural gas (especially in rural areas), AND fuel oil in such nations is probably taxed tremendously as is gasoline in many non-U.S. nations, and so in those high-fuel-cost no-natural-gas nations coal is probably the most economical reliable option for rural homes, even for middle-income rural homes. It might even be the most economical reliable option in urban homes in some nations.