Most heat recovery units have two air filters. FIM28 air filter monitors inform you when they need to be replaced. The differential pressure over both air filters is monitored. When one of these air filters get polluted, the differential pressure increases. When a threshold value is exceeded, an automatic notification message is sent via email or SMS message by SenteraWeb. SenteraWeb is the online HVAC portal. FIM28 uses the local Wi-Fi network to connect to SenteraWeb. SenteraWeb offers the possibility to adjust settings (e.g. threshold value), to monitor connected devices or to receive notifications. Based on these notifications, you are notified in time that the air filter needs to be replaced 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 heat recovery unit.