I live in an 80-year-old six-unit apartment building, and the single-pipe
steam radiator system doesn't work all that well.

I'd like to put in supplemental heating, and one good possibility seems to
be a natural gas stove-heater.

I see that there are vented and unvented models. It seems to me that
unvented might be a bit dangerous.

But I remember that years ago, many houses had room gas heaters with no
venting at all. You just lit them, and the heat filled the room -- gas fumes
and all -- and I don't remember any bad results.

Any guidance welcome.