Abstract: Devices, systems, and methods for controlling a temperature within an interior space of a building, and modifying a pre-existing temperature control system by replacing a gas heater with a heat pump. In one embodiment, a temperature control system includes a cooling unit, a heat pump, and ductwork connecting the cooling unit and the heat pump. In one embodiment, a method of operating a temperature control system includes providing to an interior space of a building heated air with a heat pump, providing cooled air with the heat pump, and providing dehumidified air with the heat pump. The method may further include providing supplemental cool air to the interior with the heat pump. In one embodiment, a method of modifying or retrofitting a pre-existing temperature control system includes replacing a pre-existing gas heater with a heat pump, while retaining a cooling unit and ductwork of the pre-existing system.