System Sensor D4120 Duct Mounted Smoke Detector

The System Sensor D4120 duct-mounted smoke detector delivers reliable HVAC smoke detection within air handling units and ventilation ducts, triggering alarm or shutdown to prevent smoke from circulating through a building. As part of the InnovairFlex series, this four-wire, photoelectric detector operates on 20–29 VDC, 24 VAC, or 120 VAC and is designed for round or rectangular duct mounting. It detects smoke in ductwork across an air velocity range of 100 to 4,000 ft/min (0.5 to 20.3 m/s) and tolerates 0% to 95% non-condensing humidity at temperatures from -4°F to 158°F (-20°C to 70°C). Its relay configuration includes a DPDT alarm relay and an SPST trouble relay, enabling integration with HVAC fire protection and building management systems. Typical applications cover air handling equipment in commercial properties and industrial facilities, where reliable duct smoke detection is essential; suitable for repair, retrofit, expansion, and replacement projects. Common replacements include System Sensor D4120W, DNR, and DH100ACDC.