Fall tune-up checklist (before the first cold snap)

The first 30°F night in October separates households that did fall maintenance from households that didn't. The latter find us at 11pm. Don't be the latter.

What you can do yourself

1. Replace the filter. If you only do this twice a year, do it in spring and fall.
2. Run the heat for 15 minutes on a cool morning. The first time you turn on a furnace after summer, it'll smell briefly — dust burning off the heat exchanger. Open a window, let it run, confirm hot air is actually coming out.
3. Check the thermostat batteries. Replace them every fall whether they need it or not. Cheap insurance.
4. Look for blockage at the venting. Gas furnaces vent through PVC out the side of the house or through a chimney. A bird's nest or a clogged intake will shut the system down on the coldest day. Eyeball the outside terminations for obstruction.
5. Test the carbon monoxide detectors. Press the test button. Replace the batteries. If the detector is more than 7–10 years old (check the date on the back), replace it. Combustion equipment + winter sealed-up house = the time of year these matter most.

What we do on a fall tune-up

• Combustion analysis. We measure CO, CO₂, O₂, and stack temperature on gas equipment. This is how we catch a cracked heat exchanger before it becomes a safety call. Most contractors skip this. We don't.
• Clean the flame sensor. The #1 cause of a furnace that lights, runs for 30 seconds, then shuts off. A 5-minute job that prevents a midnight no-heat call.
• Inspect the heat exchanger with a borescope on accessible models. Cracks, rust, scaling.
• Test ignition components — hot surface igniter resistance, pilot assembly on older units, spark gap on others.
• Check pressure switches and gas pressure. Manifold pressure should be set to manufacturer spec. Out-of-spec gas pressure causes everything from short cycling to soot buildup.
• For heat pumps: verify reversing valve operation, defrost cycle initiation, and aux heat staging.