Now that our dry firewood is pretty much exhausted, we are finding it harder to stand nights that still drop below zero (this morning they still announced a frost warning!)
In an act of desperation, I opted to purchase a heater - but I didn't want a really large one, as I'm hoping this is just a very temporary need.
We brought it home, and I fired it up. It seemed to raise the temperature in the yurts at a painfully slow rate of three degrees an hour. It performed much better when we took it into the 100sf bedroom yurt and curtained off that area. But we didn't want to let it burn through the night, so we turned it off once the temperature was over sixteen degrees. As an extra precaution, we also kept our carbon monoxide detector close by wherever we used the heater.
One thing of note, it seems to be a very humid heat. This was the first time we had noticed condensation or humidity during cold weather in the yurts.
The next day I instead opted to use it as a kotatsu heater in the larger yurt. This seemed a much more realistic use for it. I think this is about the best we can hope for all things considered. Best just pray for warmer weather, soon!