This work presents and verifies the model and air transfer in a horizontal, naturally ventilated air cavity that could be under a flat roof or under a building as a crawl space. In this article, this space is represented as a rectangular air channel with a cooled top and heated bottom and walls each either heated or cooled. Temperature of all wall surfaces varies along the attic space length. The model allows estimating temperatures of air and wall surfaces along the channel for a low velocity of airflow in the channel. The results of calculations were compared with a field experiment and agreed within estimated errors of the model, that is, <9%.