In case of a fancoil unit which supplies conditioned air in parallel to the floor near the bottom of the fancoil unit, the occupied zone is apt to be influenced by the draft usually. When the supply air velocity is decreased in order to avoid this, in some cases, a short circuit phenomenon occurs where the warm supplied air returns to the air inlet directly not coming into to the occupied zone. Here, with the method of three-dimensional numerical calculation similar to that introduced in the previous report, the study of the fundamental characteristics for this phenomenon and the influence of relating factors was carried out. As a result, it was shown that the short circuit phenomenon occurred at some Archimedes number frequently, and factors such as the supply air temperature, the supply air velocity, the width of air outlet of fancoil unit and the thermal characteristics of wall were deeply concerned. When the distribution of air velocity and temperature is nearly two-dimensional, a sort of hysteresis phenomena were sometme found when the short circuit is generated or not in the occupied zone under the different initial values of calculation even with the same calculating conditions.