I am looking for a ventless propane heater to install in an 8' X 36' park model mobile home with two slide out room extensions (only about 400 sq. ft. total). I bought the home used and the forced air furnace had been removed. Also I am off the grid so I prefer something that doesn't require electricity. The heater would be centrally located with the LR and kitchen on one side, hallway, bath and bedroom on the other. I am not sure how many BTU's would be required. I see them advertised for heating x amount of sq. ft. but is that one big open room with no hallways, doorways, etc.? I was also wondering if anyone has any experience with the ventless heaters and what you contend with as far as fumes. Seems to me if you are burning gas there has to be emissions of some sort. Anyway, I was hoping to draw on some of your experience before I purchase a unit and wind up disappointed.