Equipment Interface Module for all Prestige IAQ and new RedLINK VisionPRO Thermostats

Honeywell® Prestige Equipment Interface Module – Technical Product Information

The Honeywell® THM5421R1021/U Equipment Interface Module (EIM) is a centralized control interface designed for professional HVAC and building automation installations. Engineered for use with Prestige® IAQ and VisionPRO® thermostats featuring RedLINK™ wireless technology, the module enables simplified two-wire thermostat connections and provides full equipment staging and accessory integration. The EIM supports both heat pump and conventional systems, delivering advanced control of heating, cooling, humidification, dehumidification, and ventilation equipment through a single professional-grade interface.

Technical Specifications

• Product Code: THM5421R1021/U
• Manufacturer: Honeywell
• Compatible Systems:
  • All THX9421R5021 Prestige® 2-Wire IAQ Thermostats
  • All versions of Prestige® IAQ Thermostats
  • VisionPRO® Thermostats with RedLINK™ Technology
• Power Requirements: 18 to 30 VAC, 50/60 Hz
• Electrical Connections: Screw Terminals
• System Compatibility:
  • Heat Pump Systems: Up to 4 stages of heat and 2 stages of cool
  • Conventional Systems: Up to 3 stages of heat and 2 stages of cool
• IAQ Control Contacts: 3 universal IAQ terminals for humidification, dehumidification, and ventilation
• Sensor Inputs: 4 dedicated inputs for wired sensors or dry contact devices
• Enclosure Material and Color: Thermoplastic, Gray
• Dimensions: 9-5/16 inch (Height) x 4-13/16 inch (Width) x 1-5/8 inch (Depth)
• Mounting Configuration: Wall or equipment-mounted using integrated slots
• Operating Environment:
  • Temperature Range: 32°F to 120°F (0°C to 49°C)
  • Humidity Range: 5% to 90% RH, non-condensing
• Communication Interface: RedLINK™ Wireless Connection with thermostat and optional accessories
• Protection Features: Internal fuse and surge suppression for connected devices
• Field Configurability: Assignable IAQ terminals and sensor input functions through thermostat programming
• Compliance: UL Listed; FCC and Industry Canada certified for wireless operation
• Accessories (Optional): RedLINK™ Internet Gateway, Wireless Outdoor Sensor, Portable Comfort Control

Professional Summary

The Honeywell® THM5421R1021/U Equipment Interface Module provides HVAC contractors and system integrators with a flexible and centralized platform for connecting heating, cooling, and IAQ equipment to Prestige® and VisionPRO® thermostat systems. Supporting both conventional and heat pump configurations, the module offers up to six stages of operation with dedicated control for humidification, dehumidification, and ventilation. The four sensor inputs enable integration of temperature, outdoor, discharge air, or dry contact sensors for advanced system monitoring and control. Designed for professional installation, the EIM ensures reliable communication, simplified wiring, and optimized equipment performance within commercial and residential HVAC applications.