Abstract: A container and rail assembly system which holds phase change material (PCM). The container is comprised of a cuboidal shape akin to pizza box and the rail assembly incorporates rails as attachment mechanisms to affix the containers to surfaces within the conditioned space. Said container and rail assembly place the PCM in a location within the conditioned space that is not used or less likely to be used. Said container and rail assembly also place the PCM within the airflow of the conditioned space where the PCM is in closest proximity with the air that is emanating from the heating or cooling system.