Furnace Annual Maintenance

Purpose

Define the comprehensive annual maintenance protocol for residential gas, electric, and oil furnaces. Performed in fall before the heating season. The single highest-impact safety service in residential HVAC - a missed cracked heat exchanger is a carbon-monoxide poisoning risk; a missed flue blockage is the same.

Scope

Applies to:

• Residential gas-fired furnaces (natural gas + LP)
• Residential electric resistance furnaces
• Oil-fired furnaces (limited inspection only - recommend oil-tech specialist for combustion-side service)
• Modulating, two-stage, and single-stage configurations

Excludes commercial / industrial furnaces and boiler systems (separate SOPs).

Responsibilities

• Dispatcher schedules fall visits in September - October before heating demand peaks
• Lead technician runs the protocol; presents any safety-related findings before leaving
• Customer witnesses the carbon-monoxide testing + signs off on the field report

Procedure

1. Customer briefing. "I'll be inspecting the heat exchanger, testing combustion, and verifying every safety system. About 60 - 75 minutes."
2. Visual inspection - exterior. Check the cabinet for rust, soot stains around vents, damaged insulation, or signs of moisture.
3. Replace the air filter. Document size + airflow direction.
4. Open the burner compartment. Vacuum out dust, lint, and combustion residue.
5. Inspect the heat exchanger. Use a borescope or inspection mirror + light. Look for:

• Cracks (any crack = condemn furnace; CO leak risk)
• Rust-through (same)
• Carbon buildup (clean if accessible)

1. Inspect burners. Flame should be sharp, blue, and stable. Yellow tips = incomplete combustion (dirty burners or bad air-fuel mix); document and clean or adjust.
2. Check the flue. Look for obstructions (bird nests, debris), corrosion, or improper slope. Flue should rise at least ¼" per foot from the furnace to the chimney connection.
3. Test the safety switches. Limit switch (high-temp), flame rollout switch, pressure switch. Each must trip at spec or be replaced.
4. Combustion analysis. Use a combustion analyzer to measure CO (room + flue), O2, and stack temperature. Document readings on the field report.
5. Test thermocouple / flame sensor. Clean the flame sensor with fine emery cloth. A weak signal (< 1 µA on most modern sensors) means imminent ignition failure.
6. Test ignition system. Cycle the furnace 3 times. Verify it lights cleanly on first attempt each time.
7. Inspect blower assembly. Wheel for dust buildup (clean if heavy), motor bearings (oil if applicable), capacitor (test µF if PSC motor).
8. Check thermostat operation. Cycle on and off; verify temperature differential is within spec.
9. Verify carbon-monoxide detector in the home is functional. Customer should have one near sleeping areas per most jurisdictional codes - flag if missing.
10. Document combustion readings + safety-system test results on the field report.

Acceptance Criteria

• No cracks or rust-through in heat exchanger
• Flame characteristic is sharp blue with no yellow tipping
• Combustion analysis within manufacturer spec (CO < 100 ppm air-free, typically)
• All safety switches operational
• Customer signs field report acknowledging combustion readings + flue inspection

References

• ANSI Z21.47 (Gas-fired central furnaces standard)
• NFPA 54 (National Fuel Gas Code)
• Manufacturer service literature for the specific make/model
• Manuall internal: Furnace Won't Ignite - Diagnostic Tree