The flexible duct average temperature sensor utilizes several high accuracy high accuracy platinum RTD sensors spaced at equal distances. The probe is FT6 plenum rated cable and is available in various lengths. All probes are constructed to provide excellent heat transfer and a fast response. A transmitter that provides a high accuracy signal with excellent long term stability, low hysteresis and fast response is available with various ranges. A compact ABS enclosure with a hinged and gasketed cover is provided for ease of installation.