Lennox Y6548 – Honeywell THM5421R1021 is a reliable 2-Wire IAQ Equipment Interface Module designed to expand system compatibility for modern HVAC controls. This module allows Honeywell Prestige IAQ thermostats to manage advanced residential and light commercial systems using only two conductors, delivering clean installations and stable communication between the thermostat and HVAC equipment.

Engineered to support multi-stage configurations, the THM5421R1021 works with heat pump systems up to 4 heat / 2 cool or conventional systems up to 3 heat / 2 cool. It integrates indoor air quality accessories, zoning control, and equipment protection features, making it an ideal choice for upgrading older systems or simplifying new installations.

This Lennox OEM-associated module ensures precise control, improved energy efficiency, and dependable system performance. Compatible with RedLINK wireless accessories when used with the appropriate gateway (sold separately), it offers a flexible path for modernizing HVAC controls without rewiring.

 

Key Features:

• Supports 4H/2C heat pump or 3H/2C conventional systems
• Simplifies complex installations using 2-wire communication
• Compatible with Honeywell Prestige IAQ thermostats
• Integrates IAQ accessories such as humidifiers, dehumidifiers, and ventilation
• Works with RedLINK when paired with a separate gateway
• Enhances system diagnostics, staging, and equipment protection
• Ideal for retrofit or new HVAC installations

 

Specifications:

• Model: THM5421R1021
• System Compatibility: Up to 4 Heat / 2 Cool (Heat Pump) or 3 Heat / 2 Cool (Conventional)
• Communication: 2-Wire IAQ communication
• Voltage: 24 VAC
• Mounting: Wall or near-equipment panel
• Application: Residential and light commercial HVAC