A room using carbon black mortar slabs (CBMS) as the electrical floor heating element has been built in our lab. Studies showed that an electrical power of about 123.8 W/m(2) resulted in the indoor temperature rise of 10 degrees C within 330 min. Temperature distribution along the height of the room was uniform. Temperature rise was slightly higher if floor tiles rather than the wood flooring was used. In the process of heating, self-heating of CBMS has consumed more than 30% of the generated heat by Joule effect, which was advantageous for the stability of the thermal state. The indoor air absorbed over 50% of the generated heat. Results derived from repeated tests show that the electrical power of the CBMS system was stable during several cycles of heating. Further, the procedure and power consumption for the system to maintain a certain indoor temperature were studied. Continuous tests for 72 h has shown that the higher the indoor controlled temperature was, the longer the working time and the shorter the rest time in every cycle of heating were required. Accordingly, the power consumption to maintain the heat state increased with the controlled temperature increasing. (C) 2007 Elsevier B.V. All rights reserved.