Resideo Llc RTH21B/N 7 Day Programmable Thermostat

Product Description

The RESIDEO LLC RTH21B/N is a 7-day programmable thermostat built for residential heating and cooling systems. It supports 1 Heat / 1 Cool configurations and is compatible with forced air systems running gas, oil, or electric heat sources, as well as hot water heat and 750 mV millivolt systems. The thermostat offers multiple scheduling modes including 7-day, 5-1-1, 5-2, or 1-week programming, and scheduling can also be disabled entirely for manual operation. A large display with clear font makes daily use straightforward. Power is supplied by 2 AA batteries, not included. Licensed HVAC technicians and qualified installers handle residential thermostat replacements as part of standard system maintenance.

This thermostat is suited for residential applications where a simple, reliable programmable control is needed. It works with forced air systems using gas, oil, or electric heating, as well as hot water heat and 750 mV systems. It does not work with electric baseboard heat operating at 120 to 240 volts. The flexible scheduling options make it a practical fit for retrofit installations in single-stage residential HVAC systems where low-voltage thermostat wiring is already in place.

Key Features

• Supports 7-day, 5-1-1, 5-2, and 1-week programming schedules
• Compatible with forced air (gas, oil, electric), hot water heat, and 750 mV millivolt systems
• 1 Heat / 1 Cool single-stage configuration
• Large display with clear font for easy reading and daily use
• Battery-powered operation using 2 AA batteries (not included)
• Scheduling can be turned off for simple manual temperature control

Compatibility

Compatible with forced air systems using gas, oil, or electric heat sources, hot water heat systems, and 750 mV millivolt systems. Not compatible with electric baseboard heat operating at 120 to 240 volts. Designed as an OEM-style replacement for single-stage residential low-voltage thermostat applications.

Installation Notes

Installation should be performed by a licensed HVAC technician or qualified tradesperson in accordance with local mechanical codes. Always shut off power to the air handler or furnace control board before disconnecting the existing thermostat wiring. Confirm the system voltage is low-voltage (typically 24 volts) before installation, as this unit is not rated for line-voltage electric baseboard applications. Verify all wire connections are secure before restoring power and testing system operation.

Technical Specifications

• System Configuration: 1 Heat / 1 Cool
• Compatible System Types: Forced air (gas, oil, electric), hot water heat, 750 mV millivolt
• Incompatible System Types: Electric baseboard heat (120 to 240 volts)
• Programming Options: 7-day, 5-1-1, 5-2, 1-week, or scheduling off
• Power Source: 2 AA batteries (not included)
• Package Quantity: 4 per package
• Weight: 3.56 pounds
• Unit of Measure: EA

Standard Information

• Brand: RESIDEO LLC
• Manufacturer Part Number: RTH21B/N