An Internet of Things (IoT) platform is the most appropriate choice for integrating HVAC sensors into an existing network, as IoT devices are designed to connect and exchange data with other devices and systems over the internet, including HVAC sensors. By utilizing an IoT platform, the administrator can ensure that the sensors are not only connected but also able to be monitored and controlled centrally. A router, while essential for network communication, is not specifically designed for integrating environmental sensors. An access point provides connectivity for wireless devices but does not inherently offer integration and management features for HVAC sensors.