Traditional thermal resistance in heat transfer is definded as the ratio of the temperature difference to the heat flux, and it is only valid for one-dimensional, steady heat conduction without an internal source. As the definition of the temperature difference is not unique for multi-dimensional problems, the thermal resistance may be different for the same problem. In order to overcome this drawback, the thermal resistance based on the entransy dissipation rate has been defined as the ratio of the entransy dissipation rate to the square of the heat flux. This work has extended the application scope of the thermal resistance to the multi-dimensional conditions. For the same consideration, in the present work, the application scope of the thermal resistance is further extended to the non-seady heat transfer conditions based on the entransy dissipation rate. Here, the thermal resistance is called the impedance. Its applications in the determinations of the ideal volumetric specific heat of an external wall for active and passive condi tions show that the ideal volumetric specific heat is a δ function in summer or winter for the above two conditions.