Current methods for measuring energy flow rate in a pipe use a variety of invasive sensors, including temperature sensors, turbine flow meters, and vortex shedding devices. These systems are costly to buy and install. A new approach that uses non-invasive sensors that are easy to install and less expensive has been developed. A thermal interrogation method using heat flux and temperature measurements is used. A transient thermal model, lumped capacitance method LCM, before and during activation of an external heater provides estimates of the fluid heat transfer coefficient ℎ and fluid temperature. The major components of the system are a thin-foil thermocouple, a heat flux sensor (PHFS), and a heater. To minimize the thermal contact resistance 𝑅" between the thermocouple thickness and the pipe surface, two thermocouples, welded and parallel, were tested together in the same set-up. Values of heat transfer coefficient ℎ, thermal contact resistance 𝑅", time constant 𝜏, and the water temperature °C, were determined by using a parameter estimation code which depends on the minimum root mean square 𝑅𝑀𝑆 error between the analytical and experimental sensor temperature values. The time for processing data to get the parameter estimation values is from three to four minutes. The experiments were done over a range of flow rates (1.5 gallon/minute to 14.5 gallon/minute). A correlation between the heat transfer coefficient ℎ and the flow rate 𝑄 was done for both the parallel and the welded thermocouples. Overall, the parallel thermocouple is better than the welded thermocouple. The parallel thermocouple gives small average thermal contact resistance 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑅"=0.00001 (𝑚2.°C/𝑊), and consistence values of water temperature and heat transfer coefficient ℎ, with good repeatability and sensitivity. Consequently, a non-invasive energy flow rate meter or (BTU) meter can be used to estimate the flow rate and the fluid temperature in real life. / MS / Today, the measuring energy flow rate, measuring flow rate and the fluid temperature, in a pipe is crucial in many engineering fields. In addition, there has been increased use of energy flow rate meters in the renewable energy system and other applications such as solar thermal and geothermal to estimate the useful thermal energy. Some of the commercial energy flow rate meters are using an invasive sensor, has to be inside the pipe, including turbine flow meter and vortex shedding device. These systems are expensive and difficult to install. A new approach that uses non-invasive sensors, attached on the outside of the pipe, that are easy to install and less expensive has been developed by using the heat flux and temperature measurements. A parameter estimation routine was used to analyze the data which depends on the minimum root mean square 𝑅𝑀𝑆 error between the calculated and experimental temperature values. A correlation between the unknown parameter, heat transfer coefficient (ℎ), and the measured flow rate 𝑄 was done to estimate the flow rate. The results show that the new non-invasive system has good repeatability, 15.45%, high sensitivity, and it is easy to install. Consequently, a non-invasive energy flow rate meter or (BTU) meter can be used to estimate the flow rate and the fluid temperature in real life.