In this study the artificial disturbance was introduced into the natural convection field above horizontal heated sources and the stability of their convection fields was experimentally examined. The Experimental data were processed by smoothing and lowpass-filtering technique and the largest Lyapunov exponent which is one of the indicators of the chaotic characteristics was calculated. The results were arranged by the method based on a dimensional analysis. As a result, following facts are confirmed;(1)the stability-instability characteristics above the heated wire evaluated from the experimental data agree well with the analytical results, (2)the difference in the characteristics compared with the case of heated wire is large near heated cylinders, (3)the data-smoothing method based on the Kalman filter is effective to compute the largest Lyampunov exponent and (4)above the heated sources the chaotic characteristics of the thermal convection field are similar to the stability ones.