The Fenwal 12-E27121-000-05 Detect-A-Fire 225°F is a reliable fixed-temperature fire detection device designed for HVAC applications. It operates by sensing a specific temperature threshold of 225°F and triggering an alarm or control function to ensure timely fire detection. https://www.partshnc.com/12-e27121-000-05-fenwal-detect-a-fire-225f