Basement Air Question

From My memory of my Winnebago ,Its on propane if its out of the floor! You will also notice a big clue is your furnace burner on if you stand outside by the furnace burner exhaust . It will automatically come on if the inside temp difference is too great or the heat pumps cant provide enough heat When on the heat pump setting. Normally that happens as I said , if its too cold outside for the heat pumps to heat properly (40deg outside or lower), Or as I said youve set it for 70 and the temp inside is 50 the furnace will come on also as the heat pumps cant raise the temp that fast. The furnace will shut off as soon as the heat pump can keep up.
If you want just elect heat use some small aux heaters The pump will default to furnace backup. Heat pumps (reverse air conditioning ) will not work in cold temp!