Pump in HVAC systems are directly linked to pump and heat source energy, making them critical for energy savings. Typically, pumps operate at maximum speed to meet peak load conditions, leading to excessive energy consumption under partial load. Accurate flow measurement is essential for optimal pump operation, but physical sensors have limitations due to high costs, installation constraints, and space requirements. This study develops and validates a virtual flow meter using pump performance curves, heat exchange, and pressure-power theories with field data. The study developed virtual flow meters based on pump performance curves, heat exchange, and pressure-power theories. Results confirmed that the virtual flow meter using the pump performance curve theory achieved the highest accuracy.