Heat pump technology has gained an incredible market in the domain of sanitary hot water production in Southern Africa. Air source heat pump water heater is an efficient and renewable energy device for hot water production. The device is capable of generating a heating energy output of 2 to 4 units by utilizing an electrical energy input of 1 unit. The additional output energy is extracted from the ambient as aero-thermal energy. The book deals with the performance monitoring and development of mathematical models to predict the coefficient of performance using different predictors. The different models can be utilized by the heat pump manufacturers and energy saving companies to derive the savings from this technology when used to retrofit geyser.