Do It in October, Not November
First genuinely cold morning. The house is at 61, you're standing at the thermostat with your finger over the heat button, and there's a small part of you bracing for a noise you don't want to hear.
That's normal. The furnace has been sitting untouched since March. Dust settled on it. Something might have gotten bumped. And you're about to find out in front of your kids on a school morning.
The fix isn't complicated. It's ten minutes of looking at things, done on purpose, on a mild day, before you actually need heat.
Timing is the whole argument here. October in Cincinnati swings hard. Seventies on a Tuesday, 38 on Thursday. Everybody on the east side hits the heat button the same week, and that's the week the phones ring off the hook. If you find a problem on October 5th, you schedule a visit and it's an ordinary appointment. If you find the same problem on November 18th at 10pm, you're in a queue behind everybody else who waited.
Pick a 60 degree Saturday. Crack a window. Run the list below.
Filter First, Then Airflow
Change the filter before you run the system, not after. This order matters. A summer's worth of dust is sitting in that filter and in the blower compartment, and the first heating cycle is going to pull all of it across a heat exchanger that's suddenly hot. Start clean.
If you're not sure how often yours needs changing or which thickness you have, we broke that down in how often to change your furnace filter. Write the date on the edge of the new one with a marker while it's in your hand.
Then walk the house. Every room. You're doing two things.
- Open every supply register. Furniture moves over the summer. A couch slid six inches, a rug got rotated, a bed got pushed against a wall vent. People also close registers in guest rooms thinking it saves money, and it mostly doesn't.
- Clear the returns. These are the big grilles, usually in a hallway or on a wall near the stairs. If a bookcase or a laundry basket is parked in front of one, the system can't move air properly no matter how well the furnace runs.
This takes four minutes and it's the part most people skip.
Thermostat Batteries and Mode
Fresh batteries now, while it's warm out and you're not troubleshooting under pressure. Weak batteries in a digital thermostat can keep the screen lit while the call for heat never actually goes out, which looks exactly like a dead furnace.
Then switch it from cool to heat. Set the fan to auto. Push the setpoint about five degrees above whatever the room is reading, so the thermostat has a clear reason to call.
If you have a programmable or smart thermostat, look at the schedule too. Whatever cooling schedule it ran all summer is still loaded, and the setbacks are in the wrong places for heating.
Look at the Unit Before You Fire It
Go stand in front of the furnace with a flashlight before you send it a call for heat.
If it's a high efficiency unit, you also have two white PVC pipes coming out through the wall or the rim joist outside. Go look at them from the yard. Wasp nests happen. Leaf packs happen. Mulch gets piled up against them in the spring and nobody thinks about it again until fall. Both pipes need to be clear and open.
Back inside, look the cabinet over. You're checking for soot, oil residue, rust flakes on the floor under the unit, water stains, and on older units a cracked or frayed blower belt. Any of that changes the plan. If you see soot, oil residue, or visible damage inside the unit, the right move is to avoid turning the heat on and call for professional service. That's not being cautious for the sake of it. Soot means something burned that shouldn't have.
Also look at the space around the furnace. Paint cans, gas cans, boxes of holiday decorations, and stacked storage all migrate toward the furnace over a summer. Give it clear air on all sides.
Test the Detectors
Do this the same day, not eventually.
Press the test button on every carbon monoxide detector and every smoke detector in the house. Replace the batteries whether they chirped or not. It's October, it's the easiest month to remember, and it takes about as long as making coffee.
Then flip each detector over and read the date printed on the back. Detectors have a service life and they expire. A CO detector that's twelve years old will still light up and beep when you press test, because the test button checks the horn, not the sensor. If the manufacture date is old, replace the unit.
Any house running a combustion appliance needs working CO detection. If you only own one, it belongs on the sleeping floor.
The First Twenty Minutes
Now run it. Crack a window, set it well above room temperature, and let the furnace go for 20 to 30 minutes while you pay attention.
You'll likely smell burning dust in the first few minutes, and that's summer dust cooking off a hot heat exchanger. We wrote the full version of that, including how long it should last and which smells aren't dust, in why your furnace smells like burning.
What you're actually listening and watching for during those 20 minutes:
- Does it light within a minute of the call, or does it try several times first.
- Does the blower come on after the burners and stay on, or does it cycle off and on quickly.
- Any scraping, squealing, or rattling that wasn't there last March.
- Does warm air reach every register you opened, including the far corner bedroom.
- Does the smell fade as the run goes on, or does it keep coming back.
A smell that keeps returning after several full cycles, or that reads as plastic or electrical rather than dust, is not dust. Shut it down and call somebody.
What It Ran Fine Actually Tells You
Here's the honest limit of this checklist. A clean 20 minute run in October tells you the furnace starts, the blower turns, and air comes out of your vents. That's genuinely worth knowing and it's why you did it.
It does not tell you the heat exchanger is sound. It doesn't tell you the flame sensor is close to fouling, that the inducer bearings are noisy under load, that the gas pressure is off, or that the flue draft is marginal. Those show up on a 15 degree night in January when the unit is running long cycles back to back, which is the exact opposite of a mild October test.
That gap is what a real tune up covers. A technician measures things you can't see from the outside, checks combustion, inspects the exchanger, and cleans the parts that fail from being dirty rather than from being old. Our maintenance services page covers what's actually included.
Our technicians are salaried and earn no commission, and Repairs First means if a tune up turns up something small, you get quoted the small fix. Nobody here gets paid more for finding a reason to sell you a furnace.
If your first run turns up something you don't like, or you'd rather have somebody check it properly before winter, call and we'll get you scheduled. We work across Anderson Township, Mount Washington, Newtown, Mariemont, Madeira, Loveland, Milford, and Amelia. Call (513) 951-8539 or get in touch here.