Coefficient of thermal expansion (${\alpha }_T=-{\rho }^{-1}(\partial \rho /\partial T{)}_p$)

The fractional mass density decrease per temperature increase at fixed pressure. In the Boussinesq approximation, a temperature excess $\theta$ gives reduced gravity $g^{\prime }=g{\alpha }_T\theta$. It converts a heat budget into a buoyancy budget in natural ventilation.