Most processes (whether physical, chemical, or biological) produce or consume heat: measuring thermal power (the heat production rate) is therefore a typical method of studying processes. Here we describe the design of a simple isothermal heat conduction calorimeter built for use in teaching; we also provide an example of its use in simultaneously determining the rate constant and the reaction enthalpy of the first-order base hydrolysis of propyl parabene. (Contains 5 figures and 1 table.)