How about one of those infrared heaters?
That's a something. I don't have any experience per se, because my riggin has been to survive off-grid in case of catastrophe. in fact, even the jenny is an interim, and not really allowed for till now... This spring I am putting in a failover circuit in the fuse box, and a 220 plug on an exterior wall. Then the jenny just gets plugged in and will run the whole house (sans 220 and nuke). I am gathering batteries too, and solar... All *for* up in the holler, but this place is my test bed. So before too long, I will have rudimentary passive generation and enough power storage to last a while before I need to charge again, even without the solar.
Which means infrared will become feasible.
I DID buy me one of them fancy ones the Amish make, in the cherry-wood cabinet. And I used it here, believe it or not during construction when I was remodeling after purchase... Actually that was rather radical - all the way out to the studs, with plate replacement and floor replacement in about half of it...
It was a mild winter that year... Once I got dried back in I plugged that little IR heater in near the center of the place. It ran balls out all the time, but sealed up good, like the house was, though without any insulation, that little heater kept the place above freezing. And I left it run in December, when we were largely absent - and the electric on the place was about 40 bucks.
I figure four of those would probably heat this place fairly. Say over 50... But they would not be running balls out, so I can't quantify the actual cost of running them, vs BTU. But yeah... that would seem to be an option with the jenny running.