Lennox Furnace Manual G12

The Lennox G12 Series Furnace is a high-efficiency gas furnace designed for residential heating applications. This model features advanced combustion technology, variable-speed blower motors, and durable heat exchanger construction. The G12 series offers reliable performance with AFUE ratings up to 92%, quiet operation, and compatibility with various thermostat systems. Below are key sections covering safety, features, installation, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Durable aluminized steel heat exchanger, variable-speed blower motor, electronic ignition system, multi-speed inducer motor, and integrated control board.

Installation Requirements

Professional installation required. Ensure proper clearances and venting.

1. Location: Install in dry, clean area with adequate combustion air.
2. Clearances: Maintain 1-inch clearance from combustible materials.
3. Venting: Use approved PVC pipe for intake and exhaust.
4. Gas Connection: Use approved gas pipe and fittings; pressure test required.
5. Electrical: Connect to dedicated 115V circuit with proper grounding.
6. Ductwork: Ensure proper sizing and sealing.

WARNING! Gas furnaces produce carbon monoxide; proper venting is critical. Installation must comply with local codes.

First-Time Setup

Initial startup must be performed by qualified technician.

1. Verify all connections: Gas, electrical, venting, and ductwork.
2. Check gas pressure: Adjust manifold pressure per specifications.
3. Test safety controls: Verify limit switches and pressure switches function.
4. Program thermostat: Set heating parameters and fan controls.
5. Test operation: Run through complete heating cycle.
6. Measure temperature rise: Ensure within specified range.

CAUTION! Never bypass safety controls. Test carbon monoxide detectors after installation.

Technical Specifications

• Model Series: G12
• AFUE Rating: Up to 92%
• Input BTU/h: 40,000 - 120,000 (varies by model)
• Output BTU/h: 36,000 - 110,000 (varies by model)
• Gas Type: Natural Gas (LP conversion kit available)
• Electrical: 115V AC, 60Hz, 5-10 Amps
• Blower Motor: Variable-speed ECM
• Filter Size: 16x25x1 inches (standard)
• Venting: 2-3 inch PVC
• Sound Level: < 65 dBA
• Warranty: 20-year heat exchanger, 5-year parts

Controls and Settings

Integrated control board with diagnostic LED. Access via front panel cover.

Control Board Features: Status LED (flashing codes for diagnostics), dip switches for configuration, terminal strip for thermostat connection.

Thermostat Settings: Heat mode selection, fan control (auto/on), temperature setpoints, system mode (heat/off).

Configuration: Blower speeds, timing delays, accessory integration via dip switches.

Operating Instructions

Normal operation controlled through thermostat.

1. Set thermostat to desired temperature in HEAT mode.
2. Furnace will initiate heating cycle when room temperature drops below setpoint.
3. Inducer motor starts first to establish draft.
4. Hot surface igniter heats up, gas valve opens.
5. Burners ignite, heat exchanger warms.
6. Blower motor starts after heat exchanger reaches temperature.
7. Cycle continues until thermostat satisfaction.

Tip: Keep thermostat away from heat sources and drafts for accurate temperature reading.

Maintenance Procedures

Regular maintenance ensures efficiency and longevity.

1. Monthly: Check and replace air filter if dirty.
2. Seasonal: Inspect vent pipes for obstructions.
3. Annual: Professional inspection and cleaning recommended.
4. Burner inspection: Clean burners and check flame pattern.
5. Heat exchanger: Visual inspection for cracks or damage.
6. Blower assembly: Clean blower wheel and housing.
7. Drain system: Clear condensate trap and drain lines.

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

Safety Features

Multiple safety systems protect against hazardous conditions.

Care & Cleaning

Regular cleaning maintains efficiency and prevents issues.

1. Air Filter: Replace every 1-3 months during heating season.
2. Vent Pipes: Keep clear of debris, snow, or obstructions.
3. Burners: Professional cleaning annually.
4. Blower: Vacuum accessible areas annually.
5. Drain System: Flush condensate lines seasonally.

CAUTION! Never use water or liquid cleaners on electrical components. Always disconnect power before cleaning.

Regulatory Information

UL listed and ANSI certified. Complies with ASHRAE standards. Manufactured to meet DOE efficiency requirements. This product contains materials that may be hazardous if improperly handled. Dispose according to local regulations. For technical support or warranty service, contact Lennox Industries at 1-800-9-LENNOX or visit www.lennox.com.

Troubleshooting

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

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