Humidification sensors and transmitters affect humidifier output and, therefore, affect a humidification system's ability to meet design requirements. Sensor and transmitter readings must be accurate and pertinent. Figure 1 shows recommended locations for sensors and transmitters. Figures 2 through 4 also show recommended locations for high limit humidistats and airflow proving switches. Note: Do not interchange duct and room humidity devices. Room humidity devices are calibrated with zero or little airflow, whereas duct humidity devices require air passing across them.