Six Things to Check Before You Turn the Heat On for the First Time
Late October, first genuinely cold night, and somebody walks over to the thermostat and moves it to heat for the first time since April. Two things can happen next. Either the house fills with that burnt-dust smell for a quarter hour and then gets warm, or nothing happens at all and the morning starts with phone calls to contractors alongside half the county.
Which one you get was mostly decided a month earlier. The equipment sat untouched all summer while dust settled on the heat exchanger, thermostat batteries drained, something built a nest in the flue, and condensate dried into residue around the burner. None of that announces itself. It waits for the first call for heat.
So the argument for checking things in September comes down to timing. Whatever you find lands in a calm schedule instead of an emergency one. A tech booked in mild weather arrives at a normal rate with parts available at the supply house, while the same heating system repair service on the first freezing Saturday means after-hours pricing and a two-day queue behind everyone else who waited.
Below: six checks that fit in one evening, a test run worth doing deliberately, and how to sort what you find into things you handle, things that go on a schedule, and things that mean shutting the system down tonight.
Set Aside an Evening in September
Budget about an hour. Twenty minutes of that is the test run, where you mostly stand around listening.
Bring a flashlight, a new filter, a screwdriver, a couple of AA batteries and a step ladder. That’s the whole kit.
Why September rather than November: contractor schedules have room, supply houses have stock, and at 60 degrees outside a furnace that refuses to start is an inconvenience instead of a crisis with pipes at risk.
One boundary before the list. Everything here is visual inspection and a controlled startup. Opening the combustion chamber, touching gas piping, or pulling a heat exchanger belongs to somebody licensed, and there’s no clever workaround worth trying.
The Six Checks
Order matters a little. The airflow items come first so the test run at the end happens with a clear path, which is the only way the sounds and timings mean anything.
1. The filter
Everything that circulated during four months of cooling went through this filter. A loaded one restricts airflow across the heat exchanger, the furnace runs hotter than it was built to run, and the high-limit switch shuts it down mid-cycle.
Replace it whether or not it looks bad. Write the date on the cardboard frame with a marker so next year isn’t guesswork. Check the arrow, which needs to point toward the blower, and gets installed backwards constantly.
Worth a thought: MERV rating. A very dense filter in an older duct system creates the same restriction a dirty one does, so a high number does not automatically buy you cleaner air.
2. Registers and returns
Closed dampers and a sofa parked over a grille raise static pressure across the entire system, and the furnace pays for it the same way it pays for a dirty filter.
Open every supply register, including the guest room and the finished basement nobody uses. Clear furniture and rugs off the return grilles. Check whether any branch dampers got set for summer and never moved back.
Signs something’s wrong here: whistling at a register, or a door that pulls itself shut when the blower runs.
3. The thermostat
Dead batteries produce more “my furnace won’t start” calls than any mechanical fault in the building.
Swap the batteries. Set the mode to heat, raise the setpoint five degrees above room temperature, and listen for the click. Then count how long until anything happens downstairs.
On programmable models, check the schedule left over from last winter and look for a Hold that got set in March and forgotten. Both cause behavior that reads as equipment failure.
4. The area around the furnace
A burner needs combustion air, and the storage that accumulated around it since spring cuts into that supply while creating a fire hazard nobody planned.
Clear thirty inches on all sides. Get the paint cans, solvents, cardboard and stored paper out of there entirely. Look at the louvered vent in the utility room door if there is one. Check the floor for rust staining left by last winter’s condensate.
While you’re down there, note anything for the tech: soot marks on the cabinet, rust along the seams, standing water in a drain pan.
5. The flue outside
Summer belongs to birds and wasps, and a flue is an appealing piece of real estate. High-efficiency systems venting through PVC have a different issue, where the termination gets blocked at ground level by leaves and mulch.
Find where the vent exits the house. Confirm the screen is clear. Check that shrubs, mulch and lawn edging aren’t crowding the opening. On metal flue pipe, look for separated sections and rust at the joints.
Corrosion or a joint that’s pulled apart goes on the call-now list, not the call-eventually list.
6. Carbon monoxide detectors
Detectors expire. Seven to ten years from the manufacture date printed on the housing, regardless of whether the unit still chirps when tested.
Press the test button. Read the date. Confirm there’s a detector on every level and one near the sleeping areas, since a single unit in a hallway does not cover a three-story house.
The Twenty-Minute Test Run
Do this on a quiet weeknight rather than an hour before company arrives, because you want to hear the thing.
Raise the setpoint five degrees and note the time. Watch how long passes between the call for heat and the burner lighting, which should be seconds rather than minutes. Go downstairs and listen through the first two minutes. Walk the house and check flow at the farthest register from the furnace. Then leave it alone for twenty minutes.
Smells. Dust burning off for the first ten or fifteen minutes is expected and always alarming the first time. Burnt smell still present after an hour is not. Sulfur or rotten eggs means leave the house and call the gas utility from outside, and that call comes before any thought about a contractor.
Sounds. A click at ignition followed by steady blower hum is what normal sounds like. A whump or small boom when the burner lights is delayed ignition, worth writing down and reporting. So is grinding, squealing or metallic knocking.
Cycling. A furnace that fires, runs three to five minutes, shuts off, then fires again is telling you about airflow or the high-limit switch far more often than about the burner. That symptom is the reason the filter check came first.
Sorting What You Found
Three buckets, sorted by consequence of getting it wrong rather than by difficulty.
You handle: filter, batteries, registers and returns, clearing storage from around the furnace, cutting back whatever grew over the vent termination, replacing an expired CO detector.
Schedule a tech: short cycling, bearing noise, weak flow at distant branches, rust along cabinet seams, water in the drain pan, and any furnace over fifteen years old that hasn’t been looked at in two seasons.
Shut it off and call tonight: sulfur smell, a CO alarm, soot around the furnace, a separated flue, or a breaker that trips again right after you reset it.
What the September Visit Actually Covers
Since people reasonably wonder what they’re paying for, here’s the work list a real inspection includes.
Heat exchanger inspection for cracking, done with mirrors and instruments rather than a glance. Static pressure measured across the system. High-limit switch and flame sensor tested rather than assumed. Ignition components checked, including electrode gap and ignition delay. Venting and draft verified. On oil systems, nozzle and oil filter replacement plus combustion setup with an analyzer, which is the part that actually determines efficiency. Blower amp draw and capacitor condition, both of which carry over from the cooling season.
Set that against a night call in January at emergency rates, plus whatever the wait costs in hotel bills or frozen plumbing, and the arithmetic stops being interesting.
Furnaces rarely break in October. They just spend October showing you everything they collected since April.
Homeowners who want the longer technical version of any item on this list can find seasonal service and furnace diagnostic write-ups at regionserviceco.com, published by Region Home Services, a Bensalem, Pennsylvania heating contractor in business since 1974.