The heat transfer coefficient (h), is used in thermodynamics to calculate the heat transfer typically occurring by convection. A simple way to calculate (h) is to define it through the classical formula for convection, the present study includes correlations different natural convection can be used to calculate heat transfer coefficients theoretically for the experimental tests done inside and outside close system. All the results obtained from the experimental tests, theoretical calculations and from the literatures show that, heat transfer coefficients (h) are increasedwiththe temperature increasing. The experimental results for all the tested materials appears that there are similarity for the rules of sequence step in the change of heat transfer coefficient (h) with respect to the thermal conductivity coefficients (k) of these materials, and they are in a row from the highest value to the lowest value; Copper, Aluminum, Steel and Brick respectively for both of (k) and (h). The results show a good accuracy and compatibility of the comparison between numerical results with the present experimental work, also give a good agreement between the present experimental work and the numerical results with the experimental results obtained from literature approved in this study.