Funny I was thinking about propane heaters not that long ago thinking it would be great for the garage. I'd like to be able to work in there in the winter, but it's not insulated or finished, but it could be useful to at least take the edge off but then I started to wonder how they're even vented. Though in my situation I could put it in the garage, let it run for like an hour or two, then turn it off when I go in. I'd just want to get the temp to above freezing so things like power tools work better.
I guess the answer is clear, they're not meant for indoor use. I've seen propane heaters used in outside settings with tarps around (but not air tight) where workers are say, pouring concrete or something, I think this is mostly what these are made for.
For emergency I suppose it would be ok though, like set it up in the basement pointing at the water pipes, and stay upstairs near a CO detector. Some of the heat will also go upstairs but the CO will have dissipated a bit, I think. You'd probably want to crack a basement window open a tad to let fresh air in. This would not exactly be the most efficient way for heat but work in an emergency.
Now if I were to setup something more permanent I'd probably just setup a propane furnace that is permanently installed and vented correctly with a fresh air combustion intake and exhaust. A furnace from a camper or motorhome would probably work.