Several important design parameters for the construction and operation of a Tian-Calvet heat-flow calorimeter used in the study of adsorption and catalysis are presented. Both heat transfer and adsorption dynamics must be considered in the design. Improper choice of length scales for adsorption and heat transfer, and of the temperature used in making the measurements, can result in serious errors. A general methodology for ensuring that adsorption equilibrium is achieved is discussed.