Your Furnace Knows Winter Is Coming. Do You?

Why bother tuning up a furnace that still “works”?

If the heat came on last year, it’s tempting to assume it’ll just keep going. But furnaces are a bit like that friend who insists they’re fine while limping on a twisted ankle. They can still move, sure, but they’re not exactly in top form.

A few reasons it’s worth giving your system some attention before winter:

• You catch small problems (like a weak flame sensor or dirty filter) before they become “no heat” emergencies.
• You help your furnace run more efficiently, which usually means lower gas or electric bills.
• You reduce the chance of safety issues, like carbon monoxide leaks or overheating.

Think of it less as “furnace maintenance” and more as “making sure your house doesn’t turn into a walk-in freezer in January.”

Start with the thermostat: is your furnace even getting the message?

A surprising number of “broken furnace” calls turn out to be… thermostat problems.

Take Erin, who lives in Minnesota. Her furnace “died” one November—at least that’s what she told the technician. Turned out her thermostat was still set to Cool from a warm fall day, and the batteries were nearly dead. The furnace never got the memo to turn on.

Here’s what you can do before winter:

• Switch your thermostat to Heat and set it a few degrees higher than the current room temperature. Wait and listen: do you hear the furnace start up?
• Replace the batteries if your thermostat uses them. If you can’t remember the last time you changed them, that’s your answer.
• If you have a programmable or smart thermostat, set or review your winter schedule so the house warms up before you wake and before you get home.

If the thermostat screen is blank, flickering, or unresponsive, deal with that now. It’s a cheap fix compared to an emergency furnace call when it’s 20°F outside.

The air filter test: can your furnace breathe?

If you only do one thing before winter, let it be this: check the furnace filter.

Imagine trying to run while breathing through a thick scarf taped over your mouth. That’s your furnace with a clogged filter.

Before winter:

• Find the filter slot—usually in the return air duct or inside the blower compartment.
• Slide the filter out and hold it up to a light. If you can barely see light through it, it’s time for a new one.
• Replace it with the correct size and type. Follow the arrows on the frame so the air flows the right way.

Some people, like Jake in Ohio, set a reminder on their phone every 1–3 months to check the filter. He noticed his gas bill dropped a bit and the house felt more evenly heated once he stopped letting the filter go “until I remember it exists.”

If you’re not sure what kind of filter to buy, a basic pleated filter is usually fine for most homes. Super high-MERV filters can restrict airflow if your system isn’t designed for them, so when in doubt, ask an HVAC pro.

Dust, clutter, and that scary furnace room corner

Furnaces don’t like to be smothered. They need space and air.

Before the cold sets in, take a good look around your furnace area:

• Clear boxes, paint cans, and storage bins away from the unit. Aim for at least a couple of feet of clear space around it.
• Sweep or vacuum up dust, pet hair, and cobwebs around the base and nearby floor.
• Make sure nothing flammable (cardboard, rags, chemicals) is stored close to the furnace or water heater.

Maria in New Jersey discovered that her furnace kept shutting off on very cold nights. The technician eventually found the problem: a mountain of storage boxes stacked so close around the unit that airflow was restricted. Once she cleared the space, the random shutdowns stopped.

It’s not glamorous work, but a clean, uncluttered furnace area makes everything run smoother—and safer.

Vents and registers: is the warm air trapped?

Even if your furnace is working perfectly, blocked vents can make your home feel uneven and drafty.

Walk through your house and:

• Check that supply vents (where warm air comes out) and return vents (where air gets pulled back in) aren’t hidden under rugs, behind curtains, or blocked by furniture.
• Gently vacuum the vent covers to remove dust and pet hair.

Liam, who lives in a two-story home, thought his upstairs was “just always cold.” Turned out two of the main supply vents were completely covered by thick area rugs after a room re-do. Once he freed them, the temperature difference between floors was way less dramatic.

If you like to close vents in unused rooms, be careful. Closing too many can increase pressure in the duct system and stress your furnace. A better approach is to keep vents mostly open and adjust the thermostat or talk to a pro about zoning or balancing if certain rooms are consistently uncomfortable.

The first test run: don’t wait for the first frost

A smart move is to “test drive” your furnace while it’s still mild outside.

Pick a cool-ish day in early fall and:

• Turn the thermostat to Heat.
• Set it 5–10°F above the current room temperature.
• Listen for the sequence: thermostat click, furnace start, blower fan turning on, warm air at the vents.

Pay attention to:

• Smell: A faint dusty smell for the first 10–20 minutes is pretty normal if the furnace has been off all summer. It’s usually just dust burning off the heat exchanger. If the smell is strong, smoky, or doesn’t fade, turn it off and call a pro.
• Sound: You’ll know your furnace’s normal hum. What’s not normal? Loud bangs, persistent rattling, high-pitched squeals, or a grinding noise.
• Behavior: Does the furnace start, run for a few minutes, then shut off and repeat over and over? That short-cycling can signal airflow or control issues.

Doing this test early gives you time to address problems before every HVAC company in town has a two-week wait.

Flame and burner checks: what you can safely look at

For gas furnaces, the flame color tells a story.

When the furnace is running, carefully look (through the little window or front panel opening, if accessible) at the burner flames:

• A steady blue flame with maybe a small yellow tip is usually what you want.
• Large, lazy yellow flames, or flames that flicker wildly or lift off the burner, can mean incomplete combustion or other issues.

That’s not a DIY fix. If you see odd flame behavior, shut the system down and call a licensed technician. It’s about both performance and safety.

You can, however, gently vacuum dust and cobwebs from around the outside of the burner compartment and the blower area (with the power to the furnace switched off). Just don’t start poking inside the burner assembly or adjusting gas valves. That’s where homeowner help ends and professional work begins.

For safety guidance on fuel-burning appliances and indoor air quality, you can check resources from the U.S. Environmental Protection Agency: https://www.epa.gov/indoor-air-quality-iaq

The quiet hero: your carbon monoxide detector

If your furnace burns gas, oil, or propane, carbon monoxide (CO) is part of the picture. A properly functioning system vents it safely outside. But if something goes wrong—like a cracked heat exchanger or blocked flue—CO can build up indoors.

That’s why working CO detectors matter.

Before winter:

• Test every CO detector by pressing the test button.
• Replace batteries if they’re not hardwired or sealed.
• Check the manufacture date on the back. Many detectors need replacement after 5–10 years.

Place detectors near sleeping areas and on each level of your home. If your CO alarm ever goes off, leave the house immediately and call emergency services.

You can learn more about CO safety from the CDC here: https://www.cdc.gov/co

Don’t forget the exhaust: flues and vents

Your furnace needs a clear path to get combustion gases out of the house.

For traditional metal chimneys or flue pipes, a technician will usually inspect these during a professional tune-up. But you can do a quick visual check from the ground or from inside:

• Look for visible rust, disconnected joints, or gaps in the vent pipe.
• Outside, find the exhaust outlet (for high-efficiency furnaces, it’s often a white PVC pipe on the side of the house). Make sure it’s not blocked by leaves, debris, or overgrown shrubs.

In snowy climates, like parts of Colorado or upstate New York, homeowners learn to check those sidewall vents after big storms. Packed snow can block them, causing the furnace to shut down or operate unsafely.

If you suspect any venting issue, shut the system down and call a pro—venting is not something to improvise.

When it’s time to call in a professional

There’s a line between “handy homeowner” and “person who just voided their warranty.” Knowing where that line is will save you money and headaches.

Most HVAC pros recommend a professional furnace inspection and tune-up once a year, ideally in the fall. During that visit, they typically:

• Inspect the heat exchanger for cracks.
• Check and clean burners.
• Test safety controls and ignition systems.
• Measure gas pressure and combustion.
• Lubricate moving parts where needed.
• Verify proper airflow and temperature rise.

Take Sam, who bought a 15-year-old house in Indiana. The furnace seemed fine, but he scheduled a fall checkup anyway. The tech found a developing crack in the heat exchanger and a failing inducer motor. Sam replaced the unit on his own timeline, before winter hit, instead of waking up to a dead furnace in January.

For general guidance on hiring contractors and maintaining home heating systems, sites like https://www.energy.gov offer homeowner-friendly tips on efficiency and safety.

Call a pro promptly if you notice:

• Strange smells (burning, chemical, or gas odor).
• Frequent on–off cycling.
• Unusual noises that don’t go away.
• Cold air blowing when it should be warm.
• Soot, scorch marks, or rust around the furnace or vents.

Real-life winter prep routines you can copy

Everyone’s house is different, but certain patterns show up again and again in homes that glide through winter without furnace drama.

Jordan, who lives in Chicago, treats the first chilly weekend of October like “furnace day.” He walks through a simple routine:

He starts at the thermostat, switching from Cool to Heat and bumping the temperature up a bit. While the system wakes up, he heads to the basement, swaps in a fresh filter, and clears the usual summer clutter that has migrated near the furnace. Once it’s running, he walks the house, feeling each vent for warm air and nudging furniture away from any that feel weak.

Meanwhile, Priya in Colorado added a calendar reminder for a professional tune-up every other fall, since her furnace is still relatively new. On the off years, she still does the basics herself: filter change, CO detector test, vent check, and a short test run. Her gas bills have stayed steady, and she hasn’t had a single no-heat call in eight winters.

Then there’s Mark, who learned the hard way. After waking up to a 55°F living room and a frozen pipe one January, he now schedules his tune-up for September, not November. He jokes that he’s “paying for peace of mind,” but honestly, that’s not a bad way to think about it.

You don’t need a complicated checklist. If you:

• Make sure the furnace can turn on and run smoothly.
• Keep filters clean and airflow clear.
• Watch for odd smells, sounds, or behavior.
• Keep CO detectors working.
• Bring in a pro for the deeper inspection.

…you’re already ahead of the game.

FAQ: Common questions about getting your furnace winter-ready

How early should I start preparing my furnace for winter?

Aim for early fall—September or October in many parts of the U.S. That gives you time to fix issues before the first real cold snap and before HVAC companies get swamped.

How often should I change my furnace filter in winter?

A common rule of thumb is every 1–3 months during heavy use, but it depends on your filter type, whether you have pets, and how dusty your home is. Check it monthly at first; if it still looks fairly clean, you can stretch the interval a bit.

Is a yearly professional furnace tune-up really worth it?

For most homes, yes. It can help catch safety issues, improve efficiency, and extend the life of the system. If your furnace is older (10+ years), that yearly visit becomes even more important.

What’s a normal smell when I first turn on the heat?

A light, dusty smell that fades within an hour or so is common when you first run the furnace after months of being off. If the smell is strong, smoky, chemical, or doesn’t go away, turn off the system and call a professional.

How do I know if my furnace is unsafe to run?

Warning signs include soot or scorch marks around the unit, persistent strange smells, yellow or flickering burner flames, frequent shutdowns, and any carbon monoxide alarm going off. If you suspect a safety issue, turn off the furnace, leave the house if CO is involved, and contact a professional or emergency services.

For more information on heating safety and carbon monoxide, you can visit:

• CDC carbon monoxide safety: https://www.cdc.gov/co
• EPA indoor air quality basics: https://www.epa.gov/indoor-air-quality-iaq
• U.S. Department of Energy home heating tips: https://www.energy.gov

Get these simple steps done before the cold really settles in, and you’ll be able to nudge that thermostat up on the first freezing night with confidence—no crossed fingers required.