How Often Should a Gas Furnace Be Maintained?
A gas furnace should be professionally serviced once a year by a licensed HVAC technician. Annual maintenance keeps the furnace running safely and efficiently, catches problems before they become breakdowns, and is essentially required to keep manufacturer warranties valid. For southern New Hampshire homes that run heat seven months a year, it is one of the highest-payoff things a homeowner can stay on top of.
When to schedule
The right window is late summer through October, before the first cold snap. Demand is lighter, scheduling is easier, and any problems found can be fixed before you actually need heat. Our schedule fills fastest right after the first 20°F night of the season.
What a complete gas furnace tune-up includes
A proper annual service covers a long checklist. The high-impact items:
Combustion analysis
The single most important safety check. A digital analyzer measures the exact composition of the flue gases (CO, CO2, O2, and stack temperature). Proper combustion should produce:
- CO under 50 parts per million in the flue (manufacturer specs vary)
- CO2 in the manufacturer's specified range (typically 8 to 10 percent for gas)
- Stack temperature in the manufacturer's specified range
Out-of-range readings point to a burner that needs adjustment, a compromised heat exchanger, or a venting problem.
Heat exchanger inspection
The heat exchanger separates combustion gases from the air you breathe. Cracks or holes let CO into the home. A technician inspects visually and, when access allows, with a borescope. A failed heat exchanger is a hard-stop reason to red-tag and replace the furnace.
Burner inspection and cleaning
Burners accumulate rust, dust, or spider webs that disrupt the flame. Cleaning and adjustment restore proper combustion. A yellow or flickering flame instead of a steady blue signals something is wrong.
Ignitor and flame sensor
Modern furnaces use a hot-surface ignitor, a small ceramic element, instead of an old-style pilot light. Ignitors degrade over time and are a common cause of no-heat calls; a weak one shows up in pre-failure resistance testing, and replacing it during a tune-up is cheap insurance against a January failure. The flame sensor is a small metal rod that confirms ignition; oxidation on it causes intermittent shutdowns, and cleaning takes minutes.
Blower assembly
- Confirm the blower wheel is clean (dust on the blades cuts airflow significantly)
- Inspect the blower motor for proper amperage draw
- Verify the capacitor is at the correct microfarad rating
- Listen for bearing noise that signals motor end-of-life
Air filter
Replace the filter or note when it is due. A clogged filter is the most common reason a furnace overheats and shuts down on safety, and a frequent cause of the January no-heat call.
Gas pressure and connections
- Measure inlet and manifold gas pressure against manufacturer specs
- Inspect gas line connections for leaks using leak detection solution or a gas leak detector
- Verify the gas shut-off valve operates properly
Venting and intake
For high-efficiency condensing furnaces with PVC venting:
- Inspect both intake and exhaust pipes for blockages, separations, or animal nesting
- Verify the condensate drain is clear and the trap is functioning
- Check the venting slope
For non-condensing furnaces with metal venting:
- Inspect the flue for rust, separation, or blockage
- Verify the draft inducer is operating correctly
Safety controls and thermostat
- Test the high-limit switch
- Test the pressure switch (induced-draft furnaces)
- Test the flame rollout switch
- Verify thermostat operation and accuracy
Why annual service pays off
Gas furnaces produce carbon monoxide as a normal byproduct of combustion. Properly vented, none of it reaches living spaces; a cracked heat exchanger, blocked vent, or improper combustion can change that, and annual combustion analysis is the most reliable way to confirm safe operation. Service also prevents most midwinter no-heat calls, which usually trace back to a clogged filter, weak ignitor, sticky pressure switch, or dirty flame sensor. A properly tuned furnace can use up to 5 to 15 percent less fuel than the same unit with degraded combustion or restricted airflow. And most major manufacturers (Bosch, Trane, Lennox, Goodman, Carrier, Rheem) require documented annual professional service to keep warranty coverage, so skipping a year can void coverage on a several-thousand-dollar repair.
What homeowners can do between visits
- Check or change the air filter monthly
- Keep at least 30 inches of clear space around the furnace
- Listen for unusual noises during operation
- Watch for any soot or scorching near the burner area
- Test CO detectors monthly and replace batteries annually
Schedule a tune-up
If your gas furnace has not been serviced in over a year, or you want to get on a regular maintenance schedule, contact A.J. LeBlanc Heating or call 603-623-0412. Serving New Hampshire families since 1928.
Frequently Asked Questions
How often should I service my gas furnace?
Once a year, ideally in late summer or early fall before the heating season begins.
Is annual service required for the warranty?
For most major manufacturers, yes. Warranties typically require documented annual professional service to remain valid.
What is the best time to schedule furnace maintenance?
September and October. Demand is lighter and any problems found can be addressed before you actually need heat.
Can I service my furnace myself?
Filter changes and visual inspections, yes. Combustion analysis, gas pressure adjustment, heat exchanger inspection, and electrical work require a licensed technician with proper instruments and (in NH) a gas fitter license.
How long does a tune-up take?
A complete tune-up typically takes 45 to 90 minutes depending on the system, accessibility, and what is found during the inspection.