Energy consumption, thermal environment and environmental impacts were analytically and experimentally studied for different types of heat emitters. The heat emitters studied were conventional radiator, ventilation radiator, and floor heating with medium-, low-, and very-low-temperature supply, respectively. The ventilation system in the lab room was a mechanical exhaust ventilation system that provided one air change per hour of fresh air through the opening in the external wall with a constant temperature of 5 degrees C, which is the mean winter temperature in Copenhagen. The parameters studied in the climate chamber were supply and return water temperature from the heat emitters, indoor temperature, and heat emitter surface temperature. Experiments showed that the mean supply water temperature for floor heating was the lowest, i.e. 30 degrees C, but it was close to the ventilation radiator, i.e. 33 degrees C. The supply water temperature in all measurements for conventional radiator was significantly higher than ventilation radiator and floor heating: namely, 45 degrees C. Experimental results indicated that the mean indoor temperature was close to the acceptable level of 22 degrees C in all cases. For energy calculations, it was assumed that all heat emitters were connected to a ground-source heat pump. Analytical calculations showed that using ventilation radiator and floor heating instead of conventional radiator resulted in a saving of 17% and 22% in heat pump's electricity consumption, respectively. This would reduce the CO2 emission from the building's heating system by 21% for the floor heating and by 18% for the ventilation radiator compared to the conventional radiator. (C) 2015 Elsevier B.V. All rights reserved.