A heating and/or cooling system for maintaining an environment at a desired temperature. The heating and/or cooling system includes a heat pump, a temperature sensor disposed to measure a temperature of the environment, and a system controller. The system controller may be configured to control a condensing temperature within the condenser such that the condensing temperature is set as low as possible while maintaining the condensing temperature a predetermined amount above the desired temperature that is being maintained. The system controller may also be configured to control the evaporating valve in order to vary, based on the measured temperature, an evaporating temperature in order to reduce the difference between the evaporating and condensing temperatures.