Most control systems are temperature controlled, relying on constant minimum ventilation rate (MVR). A survey on the different conventional control systems used was conducted. Less than half of those surveyed used the recommended MVR settings. Under or overestimating MVR settings can negatively affect relative humidity (RH) and contaminant concentrations in the barn. A system that could automatically adjust ventilation according to room humidity and improve the overall conditions in the building and optimize energy requirements would be very useful. A computer model was developed to evaluate the benefits of temperature and humidity control (THC) systems that take into account the room RH over a more conventional temperature control (TC) system. Simulations comparing heating and ventilation systems were based on average temperature, energy demand and respective fluctuations of humidity and CO2 concentrations. Overall, the strategy selected as being optimum was THC with proportional control, a 75% RH set point and a proportional band of 5%.