When should you turn your furnace on in Missouri? Not when it gets cold — try today, on a mild day, for about ten minutes. We pulled three heating seasons of our own service calls to answer this, and the pattern is the same every year: our no-heat calls go from almost zero to completely slammed in the third or fourth week of October. If something is wrong with your furnace, you’ll want to find out in September, while an appointment with a quick turnaround still exists.
What our own dispatch data shows
Most articles on this question say “before it gets cold” and leave it there, but we went and looked at 544 no-heat calls across three heating seasons.
| Season | First no-heat call | The week it broke open |
|---|---|---|
| 2023 | September 26 | Week of Oct 27: 39 calls |
| 2024 | September 6 | Week of Oct 13: 11 calls |
| 2025 | October 10 | Week of Oct 20: 18 calls |
Three different years, but all the same window. The third or fourth week of October, the phones go from quiet to overwhelmed.
In addition to October, the first week of December is equally slammed. In each of the last two years, we had 30+ calls that first week. So waiting past the October cold snap doesn’t just put you behind the October rush, it puts you into December, when everyone who limped along through November and Thanksgiving calls at the same time you do.
One more number worth noticing. Every single year, somebody found out early — our first call of the season came September 26, September 6, and October 10. Those homeowners turned their heat on to check, found a problem, and got an appointment that week instead of sitting in a line.
That’s the whole point of this page: turn your furnace on before you need it.
The ten-minute test: how to turn your furnace on safely
Here’s how to turn your furnace on for the first time this season. Pick a mild day. This takes about ten minutes and costs nothing.
- Go to your thermostat and switch it from cool to heat.
- Turn the target temperature up about five degrees above the current room temperature.
- Let it run for ten to fifteen minutes. Don’t turn it on for thirty seconds and walk away — a lot of problems don’t appear until the furnace has been running a while.
While it runs, check four things.
1. Did it actually fire?
You should hear the inducer motor start, then the burners light, then the blower come on roughly thirty seconds later. If the blower is running and the air coming out is cold, the furnace isn’t firing.
2. Does it stay running?
A furnace that lights and then shuts down after a few minutes is telling you something — usually an airflow problem or a safety switch doing its job. Note what happened and call us.
3. What does it smell like?
Burning dust is normal for the first few minutes of the season. Dust settles on the heat exchanger all summer and burns off. It should clear within five-ten minutes.
What isn’t normal: a smell that never clears, anything electrical or like burning plastic, or anything that smells like gas. If you smell gas, leave the house and call your gas utility from outside.
4. Test your carbon monoxide detectors
While you’re standing there, push the test button on every level of the house, especially near bedrooms. That detector is the only thing in your home that can actually sense carbon monoxide.
Why turn your furnace on in September instead of November
Two reasons, and we’ll be honest that one of them is ours.
Yours: in September, a problem is an inconvenience. In late October, it’s an emergency, and you’re behind a queue that could be thirteen calls deep in a single day. In December, it’s even worse.
Ours: we’d rather you call us in September. It’s calmer work on a normal schedule, and nobody is sitting in a cold house waiting on us. That isn’t generosity — it’s the same interest you have, pointing the same direction.
Your furnace also sat idle from roughly May through October, through the most humid months of the year. Condensation forms, Flame sensors corrode, Insects move in and we pull nests out of burner compartments every fall. Ten minutes in September is how you find that out before it’s late.
When to call instead of troubleshooting
Call us and don’t keep testing if the furnace won’t fire at all, if it lights and shuts down repeatedly, if a smell doesn’t clear after fifteen minutes, or if a CO detector has ever alarmed.
And anything involving gas, combustion, or venting is technician work. Not because homeowners aren’t capable, but because the failure modes involve carbon monoxide.
Related questions
When should I turn my furnace on for the first time? On a mild day in September or early October, before the first cold snap. In our service area the no-heat rush begins the third or fourth week of October, so testing before then means a problem gets a normal appointment instead of an emergency one.
Why does my furnace smell like burning when I first turn it on? Dust settles on the heat exchanger over the summer and burns off when the furnace first runs. That smell is normal and should clear within five to ten minutes. A smell that doesn’t clear, or that smells electrical or like gas, is not normal.
How long should I run my furnace to test it? Ten to fifteen minutes. Shorter than that and problems like short-cycling or airflow restrictions won’t have time to show up.
Is it bad to turn the furnace on when it’s warm outside? No. Running it briefly on a mild day is exactly how you test it safely, with time to fix anything you find.
What temperature should I turn my furnace to in Missouri? There’s no single number — it depends on your house and your comfort. Most Missouri homeowners start running heat regularly in late October, which is precisely why the test should happen before then.
Next step
If your ten-minute test turned up anything — no ignition, short cycling, a smell that lingers — call us now while the schedule is still normal.
Schraer Heating & Air Conditioning, serving the St. Louis Westplex since 1946: Warren, Montgomery, St. Charles, Lincoln, Franklin, and St. Louis Counties. Schedule service or call 636-200-3276.
636-200-3276