Sustainable energy sources are most often regarded as including renewable sources and usually also technologies that improve energy efficiency. Various techniques which combines heat emission and ventilation air supply have here been used to improve energy efficiency of heat emitters. The idea is to boost convective heat transfer by leading cold ventilation supply air through the heat emission device before it enters the room. As a result, a lower water temperature in the heat emitter is sufficient to provide the required heat output. Decreased supply water temperature to heat emitters results in energy savings in production and distribution of warm water for heating purposes. In heat pumps, for example, the condensation temperature can be lowered, which results in an increased Coefficient of Performance (COP) value. Results of this evaluation show that it is possible to lower the system supply temperature from 55 °C to 45 °C. Two different systems, i.e. a modified ventilation radiator and a thermal baseboard, were evaluated with Computational Fluid Dynamics (CFD) calculations, analytical models and measurements. Correct design parameters are critical for heat transfer conditions but also for the ventilation and thermal comfort conditions in the room. This study shows that combined heat emission and ventilation supply can provide a better overall performance compared to most conventional systems. Thermal radiation from enlarged heat emission surfaces (baseboard) can contribute to decreased room air temperature levels with constant operative temperature (comfort) levels. A lower room air temperature means energy savings both by decreased heat transmission through the building shell and by losses related to outgoing ventilation air. A correlation between sustainability and exergy is discussed in the report as well as the influence of indoor air quality and thermal comfort on health and work productivity.