This work presents a computational simulator created to estimate the behavior of a greenhouse fitted with a solar-thermal collection system and an auxiliary propane-butane (LPG) heating system. The simulator enables parametric studies on the following variables: size and design of the greenhouse, construction materials, crop, geographic location (climate) of the site, type and number of solar collectors, thermal storage volume, and type of temperature control. The simulator calculates the energy consumption in the auxiliary heater needed to keep the temperature of the greenhouse within the established limits. The simulator was developed using TRNSYS (Transient Energy Systems Simulation Tool). For a given set of parametric values, the program analyzes a year of operation and simulates the operation of the system at 10-minute intervals. Energy expenditures are summed throughout the year of operation, producing yearly totals that can be compared with the results from different parametric combinations. We present an economic analysis that considers a project life of 10 years, the cost of the solar collection system, thermal storage, and auxiliary heater, as well as the cost of LPG and inflation. Our analysis shows how to reach an optimal design of the heating system that will maximize the operation profits