I did not believe in them until I got one. Just this week I did an experiment. I arrived at my camper at 5:49. Outside temp 41 inside 42. 7pm-50°, 8:10-56°, 8:50-58° I am a camp host. This is my primary source of heating. Obviously it is not as fast as an electric heater or propane furnace. It does maintain the heat very well. Mine is ducted. I keep it set about halfway. Kept me toasty when the outside temps were in the mid 30s. I do use a small electric heater for immediate heat. But it is always in my way.
Nancy-7 year US Air Force vet married to Joe-22 year retired US Air Force vet
2008 Nissan Pathfinder
2014 Jayco Jayflight Swift 264BH