Lennox G20 Furnace Manual

The Lennox G20 Furnace is a high-efficiency gas furnace designed for residential heating applications. It features advanced combustion technology, multiple firing rates, electronic ignition, variable-speed blower motor, diagnostic LED system, and compatibility with various thermostat systems. Below are key sections for safety, features, installation, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Installation Requirements 3. First-Time Setup 4. Specifications 5. Controls and Settings 6. Venting and Combustion Air 7. Operation Modes 8. Maintenance Procedures 9. Safety Features 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Stainless steel heat exchanger, variable-speed blower motor, electronic ignition system, pressure switches, flame sensor, diagnostic LED, gas valve, and control board.

Feature	Description
Heat Exchanger	Stainless steel construction for durability and efficiency
Blower Motor	Variable-speed ECM motor for quiet operation
Ignition System	Hot surface electronic ignition
Pressure Switches	Ensures proper venting operation
Flame Sensor	Monitors burner flame
Diagnostic LED	Displays error codes for troubleshooting
Gas Valve	Modulating valve for precise gas control
Control Board	Microprocessor-based control system
Air Filter	Standard 1-inch or 4-inch media filter compatible
Thermostat Connections	Compatible with conventional and smart thermostats

Installation Requirements

Professional installation required. Ensure proper clearances and venting.

Location: Install in approved location with proper clearances to combustibles.
Venting: Use approved PVC pipe for direct vent installation.
Gas Supply: Connect to proper gas line with sediment trap.
Electrical: Connect to 120V AC power with proper grounding.
Drain Lines: Install condensate drain lines with trap.

WARNING! Installation must be performed by qualified HVAC technician. Improper installation can cause fire, explosion, or carbon monoxide poisoning.

First-Time Setup

Initial startup must be performed by qualified technician.

Verify installation: Check all connections, clearances, and venting.
Gas pressure: Set manifold pressure according to specifications.
Electrical: Verify proper voltage and grounding.
Startup sequence: Follow manufacturer's startup procedure.
Test operation: Verify proper heating cycle and safety controls.

CAUTION! Never attempt to adjust gas pressure or perform startup without proper training and equipment.

Specifications

Input Capacity: 40,000 to 120,000 BTU/h (varies by model)
AFUE Rating: Up to 96% efficiency
Gas Type: Natural gas or propane (conversion kit required)
Electrical: 120V AC, 60Hz, 15 amp circuit
Blower Motor: Variable-speed ECM
Sound Level: As low as 65 dB
Venting: 2" PVC pipe for direct vent
Dimensions: Varies by model (check specific model data)
Warranty: Limited lifetime heat exchanger warranty

Controls and Settings

Access control board via front panel. Diagnostic LED displays error codes.

Thermostat Settings: Compatible with single-stage, two-stage, and modulating thermostats.

Control Board: LED status lights indicate system operation. DIP switches for configuration adjustments. Blower speeds adjustable for heating and cooling modes. Gas valve modulation controlled by microprocessor.

Venting and Combustion Air

Direct vent system uses separate intake and exhaust pipes.

Vent Pipe: Use approved PVC pipe sized according to installation manual.
Clearances: Maintain proper clearances from windows, doors, and air intakes.
Slope: Ensure proper slope for condensate drainage.
Terminations: Use approved vent terminations with proper spacing.

Tip: Regular inspection of vent system required to prevent blockages.

Operation Modes

Multiple operating modes for efficient heating.

Heating Mode: Provides warm air through duct system.
Blower Operation: Variable-speed for optimal airflow.
Ignition Sequence: Pre-purge, ignition trial, main burner operation.
Shutdown Sequence: Post-purge for safety.
Standby Mode: Ready for thermostat call for heat.

WARNING! Never block air vents or returns. Maintain proper airflow for safe operation.

Maintenance Procedures

Regular maintenance required for optimal performance and safety.

Air Filter: Replace every 1-3 months depending on usage.
Annual Inspection: Professional inspection recommended annually.
Heat Exchanger: Visual inspection for cracks or damage.
Burners: Clean and inspect for proper flame pattern.
Flame Sensor: Clean annually with emery cloth.
Drain System: Flush condensate lines and trap.
Blower: Clean blower wheel and housing.

CAUTION! Turn off power and gas supply before performing any maintenance.

Safety Features

Multiple safety systems protect against hazardous conditions.

Safety Feature	Function
Flame Rollout Switches	Detects improper burner combustion
High Limit Switch	Prevents overheating
Pressure Switches	Ensures proper venting
Flame Sensor	Confirms burner ignition
Ignition Control	Safe ignition sequence
Gas Valve	Automatic shutoff on fault

Regulatory Information

UL listed and ANSI certified. Complies with national safety standards. Manufactured to meet or exceed industry standards for gas-fired furnaces. For technical support, contact Lennox at 1-800-9-LENNOX or visit www.lennox.com.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Furnace won't start	Power, thermostat, safety lockout	Check power supply; verify thermostat settings; reset if locked out.
No heat	Gas supply, ignition, filter	Verify gas valve on; check for ignition; replace dirty filter.
Short cycling	Dirty filter, airflow, high limit	Replace filter; check vents; verify proper airflow.
Blower won't stop	Thermostat, control board	Check thermostat fan setting; inspect control board.
Error codes displayed	Various system faults	Refer to diagnostic chart in service manual.

Reset Procedure: Turn power off for 30 seconds, then restore.

Service: 1-800-9-LENNOX; www.lennox.com