Honeywell THM5421R1021 Equipment Interface Module Controls up to 4-Stages of Heat

Original price was: $119.87.Current price is: $98.70.

14 in stock

SKU: 943222 Category:


What it is:

  • A device that acts as a bridge between your thermostat and your HVAC equipment, enabling more complex control and advanced features.
  • It’s compatible with select Honeywell Prestige IAQ and RedLINK VisionPRO thermostats.

Key features:

  • Controls up to:
    • 4 stages of heat and 2 stages of cool in a heat pump system
    • 3 stages of heat and 2 stages of cool in a conventional system
  • IAQ (Indoor Air Quality) management:
    • Three sets of universal IAQ contacts to control humidification, dehumidification, and ventilation.
  • Sensor inputs:
    • Four sensor inputs for wired sensors or dry contact devices, allowing integration with additional sensors for enhanced comfort and energy savings.


  • Expands control capabilities for multi-stage systems
  • Enhances IAQ management for healthier indoor air
  • Connects with additional sensors for optimized performance
  • Streamlines wiring by reducing connections at the thermostat
  • Facilitates remote access and control through compatible thermostats


  • It’s typically mounted near your HVAC equipment and wired to both the thermostat and the HVAC system.
  • Professional installation is recommended.


  • Ensure compatibility with your specific thermostat model before purchase.

Additional notes:

  • It’s not a standalone thermostat and requires a compatible thermostat to function.
  • It doesn’t have its own user interface or display.
  • Consider consulting a qualified HVAC professional for guidance on installation and compatibility.

Additional information

Weight 1.19 lbs


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