A procedure is described in which the flows of moisture by ventilation, diffusion and condensation from a room in a building are expressed in terms of their latent heat flow, and their generating vapor pressures in terms of dewpoint temperatures. This formulation permits vapor movement to be included in the environmental temperature procedure which is used to estimate temperatures in an enclosure. An example of its use is given in which relative humidity, condensation rates and environmental temperature are computed for a selection of values of background heat input, ventilation rate and degree of insulation, together with values of ambient air temperature and moisture content.