Net zero energy houses and implementation of photovoltaic (PV) technology present established method for reducing fossil fuel use and CO2 emissions. This paper deals with a type of net zero energy house defined as net zero energy cost house. It is a house where the amount of money the utility pays the house owner for the energy which is exported to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year. The possibility of achieving net zero energy cost house from old thermally non-insulated house has been analyzed in the paper. This has been accomplished by software simulation of five variations of refurbishment methods applied to the house and installation of PV system. The results have shown that the investigated house in Serbia can become net zero energy cost house in economically most profitable way by investing mostly in house refurbishment and after that investing in PV system. This paradigm is valid until the prices of PV panels and inverters become 28% of the current prices, when it would become more profitable to invest exclusively in a PV system. (C) 2014 Elsevier B.V. All rights reserved.