Lennox Furnace Manual G8

The Lennox Furnace G8 is a high-efficiency gas furnace designed for residential heating applications. This model features advanced combustion technology, variable-speed blower motor, electronic ignition system, and comprehensive safety controls. The G8 series offers reliable performance with AFUE ratings up to 98%, quiet operation, and compatibility with various thermostat systems. Below are key sections for safety, features, installation, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Durable steel heat exchanger, variable-speed ECM blower motor, hot surface ignitor, flame sensor, pressure switches, and integrated control board.

Feature	Description
Heat Exchanger	Stainless steel construction for durability and efficiency
Blower Motor	Variable-speed ECM for quiet operation and energy savings
Ignition System	Electronic hot surface ignitor for reliable starts
Flame Sensor	Safety device to detect burner flame
Pressure Switches	Verify proper venting operation
Control Board	Microprocessor-based for precise operation
Gas Valve	Modulating for precise temperature control
Air Filter	Standard 1-inch or 4-inch media filter compatible
Thermostat Connection	Compatible with conventional and smart thermostats
Safety Switches	Multiple safety interlocks for protection

Installation Requirements

Professional installation required. Ensure proper location and clearances.

1. Location: Install in dry, level area with adequate combustion air and service access.
2. Venting: Use approved PVC or metal vent pipe per local codes.
3. Gas Supply: Connect to proper gas line with sediment trap and shut-off valve.
4. Electrical: Connect to 120V AC power with proper grounding.
5. Ductwork: Ensure proper sizing and sealing for optimal airflow.

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

First-Time Setup

Initial startup must be performed by qualified technician.

1. Verify installation: Check all connections, clearances, and venting.
2. Gas pressure: Adjust manifold pressure to specifications.
3. Electrical: Verify proper voltage and grounding.
4. Startup sequence: Follow manufacturer's startup procedure.
5. System check: Verify proper operation of all safety controls.
6. Commissioning: Test complete heating cycle and safety features.

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

Technical Specifications

• Model Series: G8
• Fuel Type: Natural Gas or LP (with conversion kit)
• Input BTU/h: 40,000 - 120,000 (varies by model)
• AFUE Rating: Up to 98%
• Blower Motor: Variable-speed ECM
• Electrical: 120V AC, 60Hz
• Gas Connection: 1/2" NPT
• Vent Size: 2" or 3" PVC (depending on model)
• Filter Size: 16x25x1 or 20x25x1 standard
• Sound Level: As low as 65 dB
• Warranty: Limited lifetime heat exchanger, 5 years parts

Controls and Settings

Integrated control board with LED status lights and diagnostic codes.

Control Board Features: Self-diagnostic capability, status LED, flame rollout switch, pressure switch, limit switches, ignitor control.

Thermostat Settings: Conventional 24V thermostat with W, R, G, C terminals. Compatible with programmable and smart thermostats.

Blower Speeds: Adjustable for heating and continuous fan operation. DIP switches on control board for speed selection.

Gas Valve: Modulating or two-stage operation depending on model. Manifold pressure adjustable by qualified technician.

Operating Instructions

Normal operation controlled by thermostat.

1. Set thermostat to desired temperature and HEAT mode.
2. Furnace will initiate startup sequence when heat is called.
3. Inducer motor starts first to establish draft.
4. Pressure switches verify proper venting.
5. Hot surface ignitor heats up.
6. Gas valve opens and burner ignites.
7. Flame sensor confirms ignition.
8. Blower motor starts after heat exchanger warms up.
9. System runs until thermostat is satisfied.

Tip: Keep thermostat setting consistent for optimal efficiency.

Maintenance Procedures

Regular maintenance ensures optimal performance and safety.

1. Monthly: Check and replace air filter as needed.
2. Seasonal: Inspect vent system for obstructions.
3. Annual: Professional inspection and cleaning recommended.
4. Burner inspection: Clean and verify proper flame pattern.
5. Heat exchanger: Inspect for cracks or damage.
6. Blower assembly: Clean blower wheel and housing.
7. Drain system: Clear condensate trap and drain line.
8. Electrical: Check all connections and components.

WARNING! Turn off power and gas supply before performing any maintenance. Some tasks require qualified technician.

Safety Features

Multiple safety systems protect against hazardous conditions.

Safety Feature	Function
Flame Rollout Switch	Detects flame outside combustion chamber
High Limit Switch	Prevents overheating
Pressure Switches	Verify proper vent operation
Flame Sensor	Confirms burner ignition
Ignition Control	Safe start-up sequence
Gas Valve	Automatic shut-off if flame not detected

Carbon monoxide detectors recommended in living spaces.

Care & Cleaning

Regular cleaning maintains efficiency and extends equipment life.

1. Air Filter: Replace every 1-3 months depending on usage.
2. Combustion Area: Vacuum dust and debris annually.
3. Blower Assembly: Clean blower wheel and motor annually.
4. Drain System: Flush condensate trap monthly during heating season.
5. Vent System: Inspect for obstructions seasonally.

CAUTION! Always disconnect power before cleaning. Use only approved cleaning methods and materials.

Regulatory Information

UL listed and ANSI certified. Complies with ASHRAE standards. Manufactured to meet or exceed industry safety standards. Natural gas models certified for use with natural gas. LP models require factory-approved conversion kit. Installation must comply with National Fuel Gas Code (NFPA 54), local building codes, and manufacturer's instructions. 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, switch	Check circuit breaker, thermostat setting, door switch
No heat	Gas supply, ignitor	Verify gas valve on, check ignitor operation
Short cycling	Filter, limit switch	Replace dirty filter, check high limit switch
Blower won't stop	Thermostat fan setting	Check thermostat fan setting (ON vs AUTO)
Unusual noises	Blower, inducer motor	Inspect blower wheel, inducer motor bearings
Error codes flashing	Control board diagnostics	Refer to diagnostic code chart in service manual

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

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