A theory is presented for the transport in porous media of water in response to a temperature gradient and the transport of heat in response to a water pressure gradient. These processes are formulated by exploiting the appropriate equation of energy dissipation and the Clapeyron equation. Several general forms of the Clapeyron equation are developed in order to readily find expressions for the transport coefficients of concern. The cause of the coupled flow processes is related to the heat of vaporization, the heat of fusion, and the partial specific heat of wetting of the soil water. The present paper applies the basic theory to the transport processes via the vapor phase. A second paper is concerned with the liquid phase.