Honeywell Home THM5421R1021/U Prestige® 2-Wire IAQ Equipment Interface Module

The THM5421R1021 is a Prestige 2-wire IAQ equipment interface module from Resideo (Honeywell Home).

RedLINK is the wireless link Resideo uses between a thermostat and the rest of the system. Instead of pulling a wire from the equipment to every sensor and module, the devices are enrolled to the thermostat or to a wireless adapter and talk to it directly — which is what makes a sensor in a room with no thermostat wire, or an outdoor sensor with no conduit to the attic, a realistic job rather than a demolition project.

Enrolment is the step that decides whether it works. Each device has to be added to the system at the thermostat or the adapter; a RedLINK device that has not been enrolled is inert, and one enrolled to the wrong system stays enrolled until it is cleared.

The equipment interface module is what makes the 2-wire installation possible. It lives at the equipment and carries all the terminals — heat, cool, fan, humidification, dehumidification, ventilation — while only two wires run up to the thermostat. On a retrofit that is the whole argument: a Prestige system on the existing pair, with no new cable through finished walls.

IAQ here means the module also drives the indoor air quality equipment — humidifier, dehumidifier, ventilator — rather than leaving each one on its own control fighting the others.

Goes with: THX9421R5021WW.

• Brand: Resideo (Honeywell Home)
• Manufacturer Part #: THM5421R1021/U
• Type: Prestige 2-wire IAQ equipment interface module
• Supply voltage: 18 to 30 Vac
• Connections: Screw terminals
• Operating temperature: -40 °F to 165 °F
• Category: RedLINK Accessories