You probably wouldn’t consider putting a water heater with its space consuming tank into your tiny home. With space being of primary consideration, what a tiny house, a small apartment, RV, Camper or boat needs is an electric tankless water heater.
In my first tiny apartment back in Switzerland I had one of those enormous tank water heaters that took away so much space in my already small one-room apartment that it was almost painful. It took forever to heat the water in it. Well, at that time I could only have dreamed about having one of these great electric tankless water heaters available today.