Heating oil is what I use. It's not the best way to heat, but I can't get gas here, and won't do wood. (See my intro post)

For backup, I've used the round non-vented indoor kerosene heaters. They work pretty well, but you have to be with them, and watch them, when they run. Doesn't happen often, but sometimes they'll go nuts and spew flame and soot as if they're built on purpose just to do that. Basically they're giant kerosene lanterns, if you remember the old railroad type lanterns as a kid.

With any of them, I have a battery powered CO detector, and a smoke detector. CO is nasty stuff as others have related on here.