In various exemplary embodiments, systems and methods for encapsulated heaters are provided. A submersible, encapsulated heating system, a submersible, encapsulated heating system with a built-in thermostat, an encapsulated heat exchanger with flow-through heating, and a liquid, floating, encapsulated heating system are disclosed. The heater includes at least one heating element within the housing. The heating element is a positive temperature coefficient (PTC) of resistance heating element. The heater includes a pair of thin, flexible foil electrode strips disposed upon opposing sides of heating element, configured for flexibility to make an intimate contact with surface areas on each heating element. Within the housing, the heating element and the pair of thin, flexible foil electrode strips are encapsulated with an inert polymer to make the heater submersible. The encapsulated heater is configured to electrically heat a medium to a predetermined temperature and to maintain the temperature of the medium.