About 2 years ago, I attended a presentation by a guy named Tim Woolf. He was a preparedness specialist for the Mormon Church (He had a website but it is no longer working).

He addresses this issue. The Mormon church tasked him with investigating home heaters. He decided on a kerosene heater. He described it as having a flat top on it that could double as a cooking surface (he just described it and I never saw it). Anyway, as part of his assignment, he allowed the natural gas to be shut off to his house for an entire winter (he lived in the Provo area of central Utah - not Minnesota, but still significantly cold). He said that it heated his house to the point that other than having to shut it down daily for refueling, they could not tell that their furnace was not running. (I'm guessing that he had 2 or 3 of them running, one in sleeping areas, one in living areas, etc., but he implied that they only used one). For the entire winter he went through less than a 50 gallon drum of kerosene.

His points were:

-Propane is not safe for indoor use because of carbon monoxide.
-It takes a lot of Propane to use as a heat source.
-The amount of propane that would have to be stored for long term heat is probably illegal to store.

Anyway, I have several propane heaters. I use one for ice fishing and I just bought the Home Depot version of the Mr Heater, and for their intended purposes they are great. I also have a Coleman 2 Burner and a Camp Chef 3 burner and I love both (I just went to Sportsmans Warehouse and bought the correct adapter hose and can run any of them off of 20 lb bottles). But if you are looking at a backup to heat your house, especially potentially for a week or 2 at a time, propane is probably not the best choice. I actually checked Home Depot on their recent clearance of space heaters to see if they had a kerosene heater and they were out of the ones that seemed appropriate for the purpose you describe.