There are many indoor pollutants in the residentia lbuildings. Of those radon is a major and harmful indoor pollutant in most countries. Radon sometimes entries to the house through building materials. High insulation and tightness in order to increase energy efficiency and to lower energy costs is led to the indoor air quality problems. Ventilation is a good method to dilute radon contaminant and maintain indoor air quality. The more fresh air is brought into the indoor environment, the better the indoor air quality can be achieved, if the fresh air comes from non polluted ambient source. However ventilation can consume a lot of energy (currently 29-59% of energy building use), especially in cold climate same as Sweden, energy consumption could be much more. Though for coping with high energy consumption the building tightness is acted very well, but for ventilation plays against. This contradiction makes a poor indoor air quality. The aim of this paper is to simulate and visualize radon treatment and mechanical ventilation rates for achieving to indoor air quality. The Fluent (CFD) program software is employed for simulation.