Currently - 7 deg F to drop to -17 again tonight then above zero for a awhile.
I have a so called milk house heater in the kitchen as it would freeze without it. Keeps it too warm while i am away now 63 deg F. I should set it lower. In MN.
There was some local sob story on social media. No disrespect intended. Some couple returned to their house here in MN. The crawl space got real cold pipes froze and the water killed the furnace then more pipes froze. Then some flooding. They were looking for a cheap plumber.
Me? I would have put a heater in the crawlspace set to go on a low temp but well above freezing. Last winter the milk house heaters were going for $20. To be supper safe use the oil filled radiator type.
Also while present in the house, I have used the propane tank top "sunflower" heaters indoors with no problems.. I had CO and explosive gas monitors just in case. They do generate humidity.