In recent years, many researchers have been attracted to the application of phase change materials (PCMs) in the production of construction materials. PCMs are substances with large latent heat capacity and their combination with building materials such as concrete and gypsum would lead to an enhancement in their thermal characteristics, mostly thermal inertia and also the capacity of storing thermal energy. One of the problems associated with the use of PCMs is the correspondence of their melting temperature range with the temperature of the ambient in which they will be used. This paper is aimed to introduce an innovative apparatus for investigating some characteristics of PCM-containing wallboards such as the amount of the reduction of maximum indoor temperature, the time delay to reach the maximum indoor temperature, and the cycling stability of PCMs in melting and freezing cycles. The compatibility of the melting temperature of the PCMs with the ambient temperature to ensure the charge/discharge process of PCMs can be studied as well. The analysis of the test results carried out by this apparatus will help the researchers to a better understanding of the thermal behavior of any kind of PCMs in many different environments. In this study, thermal performance of a precast concrete sandwich panel incorporating PEG 600 as PCM is evaluated using the introduced apparatus. (C) 2018 Elsevier B.V. All rights reserved.