Abstract: A control system for heating or cooling equipment prior to startup. A temperature sensor senses the temperature of equipment whose temperature is to be controlled. Using an input device, the user of the invention may provide input parameters such as the equipment's expected start time, the size of the equipment, and the rating of the heating or cooling device(s) to be used. A computer utilizes the input parameters and the temperature of the equipment to calculate an activation time at which the heating or cooling device(s) should begin heating or cooling the equipment to provide the equipment with a desired temperature at the expected start time. At the activation time, the computer provides an initiation signal, which causes the heating or cooling device(s) to begin heating or cooling the equipment. In a more specific embodiment, the invention may be utilized to efficiently preheat an engine in frigid conditions by selectively applying power to one or more heaters.