Air filter monitor to measure differential pressure over two air filters. Typically, this device is used to monitor the air filters in air handling units with heat recovery. When one of the air filters get polluted, the differential pressure increases. When the threshold value is exceeded, an automatic notification message is sent via email or SMS message by SenteraWeb. This air filter monitoring device can be connected to SenteraWeb via an ethernet cable or via the local Wi-Fi network. SenteraWeb is the online HVAC portal. It can be used to adjust settings (e.g. threshold value), to monitor connected devices, data logging or to receive notifications. Based on this notification, you are notified in time that one of the air filters will need replacement soon. Maintenance and air filter replacement can be scheduled ahead. The LEDs on the front cover provide a visual indication. The enclosure can be mounted on a panel or wall nearby the air filter.