We’ve got a ~1200 sq ft rental that we heat with a ventless LP wall heater. But we are quite a ways south of you, although it can get pretty cold here. I doubt the house has any insulation in the walls and it does a good job of keeping it warm at less than half throttle. There are ceiling fans in all rooms to help circulate the air. Tenant is a single guy so it suits him fine. Pretty efficient he says.