Healthy and comfort indoor air becomes more relevant for the persons working or living in buildings. Keeping the indoor air temperature in a comfortable range is common for room air conditioning. Nevertheless, keeping the moisture in a comfortable range is often neglected, as the influence of too dry or too humid air on health is underestimated. To predict the moisture content in indoor air environments over yearly periods, we enhanced a dynamic building model with a moisture balance. Using this model, we analyzed the influence of moisture recovery systems in residential ventilation on the indoor air humidity compared to heat recovery systems. The comparison shows that moisture recovery systems significantly decrease the number of hours of dry air during a yearly period.