Abstract: An apparatus and method for measuring the efficiency of a heating system in which the temperature of the flue, or stack, is measured during a heating cycle and data collected to show the elapsed time and maximum temperature achieved. This data is compared to predetermined limits and if the elapsed time and/or the maximum temperature exceeds the predetermined limits, an error message is generated that may be video, audio, and/or an email sent to a predetermined email address. Other statistics may be generated and temperature data from more than one heating cycle may be aggregated together.