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

Honeywell THM5421R1021 Equipment Interface Module for Prestige IAQ and RedLINK VisionPRO Thermostats

The Honeywell THM5421R1021 Equipment Interface Module (EIM) provides wireless equipment control for compatible thermostats, managing up to 4 stages of heat and 2 stages of cool in heat pump systems or 3 stages of heat and 2 stages of cool in conventional systems. This 24V module includes three sets of universal IAQ contacts for controlling humidification, dehumidification, and ventilation, plus four sensor inputs for wired sensors or dry contact devices.

Key Features & Benefits

• Multi-Stage Heating and Cooling Control: Controls up to 4 stages of heat and 2 stages of cool in heat pump systems and up to 3 stages of heat and 2 stages of cool in conventional systems for precise climate management.
• RedLINK Wireless Technology: Enables wireless communication between the thermostat and HVAC equipment, eliminating the need for extensive thermostat-to-equipment wiring.
• Universal IAQ Contacts: Three sets of contacts control humidification, dehumidification, and ventilation equipment for comprehensive indoor air quality management.
• Sensor Input Capability: Four sensor inputs accommodate wired sensors or dry contact devices for expanded system monitoring and control.
• 24-Volt Operation: Operates on standard 24V HVAC system voltage.
• Manual and Auto Changeover: Supports both manual and automatic changeover between heating and cooling modes.
• Heating and Cooling Applications: Designed for dual-purpose climate control in residential and light commercial installations.

Compatibility & Requirements

Compatible with all versions of Prestige IAQ Thermostats and the new RedLINK VisionPRO Thermostats. Each EIM pairs with a single thermostat and cannot operate multiple thermostats simultaneously. The system requires 24VAC control voltage. When using this module, the thermostat communicates wirelessly with the equipment, so extensive wiring between the thermostat location and the HVAC equipment is not necessary. Works with zoned hydronic systems that use 24VAC control voltage, suitable for radiant floor heating and other hydronic applications. Installation should be performed by a qualified HVAC technician.

Installation & Care

Mount the EIM near the HVAC equipment. Connect 24VAC power to the designated terminals. Wire the equipment control outputs to the corresponding heating, cooling, and IAQ equipment terminals according to the system type. Wire any sensors or dry contact devices to the four sensor input terminals as needed. Pair the module with the compatible thermostat by following the linking procedure in the thermostat menu. Verify wireless communication between the thermostat and EIM after installation. Check all equipment stages and IAQ functions for proper operation. Keep the module clean and dry. Avoid locating the module in areas subject to excessive heat, moisture, or vibration.

What's Included

• THM5421R1021 Equipment Interface Module
• Mounting hardware
• Install Instructions

Warranty & Support

This item replaces part numbers THM5421C1008, THM5421R1005, and THM5421R1013.

Frequently Asked Questions

Q: Do I need to purchase this EIM with a Prestige IAQ or RedLINK VisionPRO thermostat, or will the thermostat work on its own?
A: The EIM is only required if you want the thermostat to communicate wirelessly with your HVAC equipment. Without the EIM, the thermostat must be hard-wired directly to the equipment.

Q: Can I use this EIM to run a zoned hydronic heating system?
A: Yes, the EIM can control zoned hydronic systems that use 24VAC control voltage, making it suitable for radiant floor heating and other hydronic applications.