Lennox G8Q3 Furnace Manual

The Lennox G8Q3 is a high-efficiency gas furnace featuring multi-speed blower operation, electronic ignition, and advanced safety controls. This upflow furnace is designed for residential heating applications with AFUE ratings up to 80%, suitable for various climate conditions. Below are essential sections covering safety, installation, operation, maintenance, and troubleshooting procedures.

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

Features at a Glance

Key components: Gas valve, heat exchanger, blower assembly, electronic ignition system, pressure switches, limit controls, and diagnostic LED.

Feature	Description
Heat Exchanger	Durable aluminized steel construction
Blower Motor	Multi-speed PSC motor for airflow control
Ignition System	Direct spark electronic ignition
Gas Valve	Automatic gas control with safety shutoff
Pressure Switches	Verify proper venting operation
Limit Controls	Prevent overheating conditions
Diagnostic LED	Flash codes for troubleshooting
Filter Rack	Standard 1-inch filter accommodation
Flue Outlet	3-inch diameter for vent connection
Electrical Connection	120V AC, 60Hz power requirement

Installation

Unpack and inspect all components. Ensure proper clearances and level mounting surface.

Position furnace: Place on stable, level surface with required clearances.
Connect gas supply: Use approved gas piping; pressure test for leaks.
Install venting: Connect flue pipes according to local codes.
Electrical connections: Connect 120V power and thermostat wiring.
Ductwork: Connect supply and return ducts securely.

WARNING! Gas appliances require professional installation. Follow all local codes and manufacturer specifications.

First-Time Startup

Complete installation verification before initial operation.

Verify gas connections: Check for leaks with soap solution.
Electrical check: Ensure proper voltage and grounding.
Venting inspection: Confirm proper draft and clearances.
Thermostat setup: Install batteries and configure heating mode.
Initial ignition: Follow startup sequence per manual instructions.

CAUTION! Never bypass safety controls. Only qualified technicians should perform startup procedures.

Specifications

Model: G8Q3 Series
Input Capacity: 40,000 - 120,000 BTU/H
AFUE Rating: Up to 80%
Gas Type: Natural Gas
Electrical: 120V AC, 60Hz
Blower Speeds: Multi-speed operation
Vent Size: 3-inch diameter
Filter Size: Standard 1-inch
Operating Pressure: 3.5" W.C. natural gas
Dimensions: Varies by model size

Controls and Settings

Access control board via front panel. Diagnostic LED provides status codes.

Thermostat: HEAT/COOL/OFF selector, temperature setting, fan AUTO/ON control.

Gas Valve: Manual shutoff, pressure regulation. Blower Control: Speed taps for airflow adjustment. Limit Switches: Automatic high-temperature cutoff. Pressure Switches: Verify inducer operation. Ignition Control: Direct spark sequencing with trial for ignition.

Venting Requirements

Category I venting; follow local codes for materials and clearances.

Use approved vent materials: Galvanized steel or AL29-4C.
Maintain proper slope: 1/4 inch per foot upward from furnace.
Clearance to combustibles: Follow manufacturer specifications.
Termination: Roof or sidewall per code requirements.

Tip: Always verify draft after installation and annually during maintenance.

Operating Instructions

Normal heating cycle operation and user controls.

Set thermostat: Move to HEAT position and set desired temperature.
System startup: Inducer motor starts, pressure switch proves draft.
Ignition sequence: Hot surface igniter glows, gas valve opens.
Flame verification: Flame sensor confirms ignition.
Blower operation: Blower starts after heat exchanger warm-up delay.
System shutdown: Gas valve closes when thermostat satisfied.

WARNING! Never operate without filter. Keep combustion air openings clear.

Maintenance Procedures

Regular maintenance ensures efficient and safe operation.

Monthly: Check and replace air filter as needed.
Annual: Professional inspection and cleaning.
Blower cleaning: Remove dust and debris annually.
Heat exchanger: Visual inspection for cracks or damage.
Vent system: Check for obstructions and proper draft.
Electrical: Tighten connections and check components.

CAUTION! Disconnect power before servicing. Only qualified technicians should perform internal maintenance.

Safety Features

Multiple safety systems protect against hazardous conditions.

Safety Device	Function
Flame Rollout Switch	Detects flame outside combustion chamber
High Limit Switch	Prevents overheating conditions
Pressure Switches	Verify proper venting operation
Flame Sensor	Confirms burner ignition
Gas Valve	Automatic shutoff during malfunctions

Regulatory Information

ANSI Z21.47/CSA 2.3: Certified for natural gas operation. UL listed. Must be installed in accordance with National Fuel Gas Code (NFPA 54) and local building codes. For technical support, contact Lennox Industries at 1-800-9-LENNOX or visit www.lennox.com.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No heat	Thermostat, power, gas supply	Check thermostat setting; verify power; ensure gas valve open.
Furnace locks out	Safety device tripped	Check diagnostic LED; reset power; inspect safety controls.
Blower doesn't run	Motor, capacitor, control	Check voltage to motor; test capacitor; verify control signal.
Ignition failure	Gas, igniter, sensor	Verify gas pressure; check igniter operation; clean flame sensor.
Short cycling	Filter, limit switch, airflow	Replace filter; check limit switch; verify proper airflow.

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

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