The focus of the present research is to study a parametric simulation of a solar heating system. The system consists of vacuum solar panels, a storage tank in tank to provide heating as well as domestic hot water to a regular house. The simulation environment is Transol, a powerful software adapted for many types of solar systems. The results show the solar energy production as a function of different collector surface, accumulation volume, orientation, tilt and also shading. For all the simulations Constanta, Romania's climate is taken into consideration.