Photovoltaic systems are increasingly being used in residential buildings. The absorbed heat of PV panels is normally dissipated to the ambient air via a natural convection and radiation. This paper will describe how to convert a PV system to a PV/T system, to make it possible to utilize PV modules thermal energy for different applications as well as increasing the electrical efficiency of the panels. This paper focuses on the design development of an existing roof mounted PV system of a house in Sydney to a PV/T air system including a PV/T air collector and an air handling system from the collector back end to bedrooms of the house. Thermal and electrical energy output of the new system is examined in this study. Additionally a payback period analysis is conducted to evaluate the economic benefit of such a PV/T system.