Furnace Blowing Cold Air or Not Turning On? What to Check in Lenoir City & Farragut

A furnace blowing cold air is usually a thermostat setting, a clogged filter, or a safety switch shutting the burners off on purpose. Most of those you can check in ten minutes without opening the furnace.

Key Takeaways

• Start with the thermostat. Carrier says the most common cause of a furnace blowing cold air is the fan set to On instead of Auto.
• About two of every three Lenoir City homes heat with electricity, and two of every three Farragut homes heat with gas. If you have a heat pump, cooler air at the vent can be normal.
• If you smell gas, leave the house first, then call your gas company: LCUB at 844-687-5282 in Lenoir City, or KUB at 865-524-2911 in Farragut.

Do you have a gas furnace or a heat pump?

Find out which system you have before you troubleshoot, because “blowing cold air” means different things for each. Census figures for 2020 to 2024 show that 66.6% of homes in Lenoir City heat with electricity, either a heat pump or electric resistance heat, while 67.2% of homes in Farragut heat with natural gas. A gas furnace should put out noticeably hot air. A heat pump delivers air that’s warm but cooler than most people expect: building scientist Allison Bailes of Energy Vanguard puts heat pump supply air at about 90°F to 110°F, against around 150°F off a furnace’s heat exchanger. That gap is why a working heat pump can feel cool against your hand.

Area	Heat with natural gas	Heat with electricity	Heat with propane
Lenoir City	28.5%	66.6%	4.2%
Farragut	67.2%	31.7%	0.8%
Loudon County	28.4%	65.4%	4.5%
Knox County	31.9%	65.5%	1.6%

Source: U.S. Census Bureau, American Community Survey 2020-2024 5-year estimates, table B25040 (house heating fuel).

A few quick ways to tell what you have:

• Gas furnace: a gas meter outside, and a metal or white PVC vent pipe running from the indoor unit to the roof or an outside wall.
• Heat pump: the outdoor unit runs in winter. An air conditioner’s outdoor unit sits still all season.
• Dual fuel: both.

If yours is a heat pump, our heat pump winter guide covers defrost, steam and AUX heat. The rest of this post covers gas furnaces.

Why is my furnace blowing cold air?

The most common reason a furnace blows cold air is the thermostat fan set to On, which runs the blower nonstop and pushes room-temperature air between heating cycles. Carrier lists that first in its cold air diagnostic. Its diagnostic also covers the startup delay, a clogged filter, and two safety parts: the limit switch and the flame sensor. When a filter clogs, heat builds up inside the furnace and the limit switch shuts the burners off to protect it, but the blower keeps running to cool the unit down. A dirty flame sensor causes the same symptom a different way: the burners light, the sensor can’t confirm the flame, and the furnace shuts the burners down quickly while the fan keeps going.

What you notice	Likely cause	Can you fix it?
Cool air for the first minute, then warm	Normal blower delay of 30 to 60 seconds	Nothing to fix
Fan runs all the time, air never gets warm between cycles	Thermostat fan set to On	Yes. Switch it to Auto
Warm air turns cold, airflow feels weak	Clogged filter tripping the limit switch	Yes. Replace the filter, and call if it keeps happening
Burners light, then shut off quickly	Dirty or failing flame sensor	Call a technician
No heat, and other gas appliances are out too	Gas supply problem	Call your gas company
Water on the floor around the furnace	Clogged condensate line on a high-efficiency furnace	Call a technician
Blinking light on the furnace	Control board fault code	Note the pattern, then call

What can you safely check before calling?

You can rule out the most common causes in about ten minutes without removing a panel or touching anything inside the furnace. Work through these in order, and stop at the first one that brings the heat back:

1. Thermostat mode and setting. Make sure it’s on Heat, not Cool or Off, and set a few degrees above the room temperature.
2. Fan setting. Set the fan to Auto so the blower only runs while the furnace is heating.
3. Batteries and schedule. Replace the batteries if the screen is blank or dim. Carrier notes that a schedule can shift after a power outage or a time change.
4. Air filter. Carrier recommends changing a basic 1-inch filter every one to three months.
5. Vents and returns. Open closed supply vents and move rugs and furniture off return grilles. Closing too many vents can overheat a furnace the same way a dirty filter does.
6. Power. Check the furnace’s power switch (it usually looks like a light switch on or near the unit) and the breaker. Reset a tripped breaker once. If it trips again, leave it off and call.
7. Gas supply. If your stove or gas water heater isn’t working either, the problem is likely the gas supply, not the furnace. Call your gas company.
8. Status light. If your furnace shows a blinking status light, write down or video the pattern. Carrier advises opening the cabinet door only if your owner’s manual says homeowners can.

If the heat still isn’t right, the cause is likely a gas, ignition or electrical part, and it’s time for furnace repair.

Why won’t my furnace turn on at all?

A furnace that won’t turn on at all is most often getting no signal or no power: a dead thermostat, a switched-off power switch, or a tripped breaker. If the thermostat is calling for heat and the furnace has power, the problem is usually somewhere in its startup sequence. Carrier describes that sequence on a modern furnace as the inducer motor first, then the ignitor, then the gas valve.

What you hear when it tries to start points to the cause:

• You hear nothing at all. The likely cause is power or the thermostat, or a failed control board.
• You hear the inducer motor hum but the burners never light. The ignitor, the gas valve or the gas supply is the likely culprit.
• The burners light and then go out. This points to the flame sensor.

On an older furnace with a standing pilot light, a pilot that’s gone out stops the burners from lighting. Carrier says relighting it by the instructions on the unit is a homeowner task. If it won’t stay lit, call for service.

What do common furnace repairs cost in Lenoir City and Farragut?

Eco Home Solutions publishes flat-rate prices for two parts that can cause a no-heat call: thermostat replacement runs $250 to $800 or more, depending on Wi-Fi and system compatibility, and capacitor replacement runs $140 to $285. We give you the price before any work begins, and both figures are on our pricing page. Other repairs, like a flame sensor, ignitor or control board, depend on the make and model of your furnace, so we quote them after we diagnose the problem.

If you replace within a year, our 100% Repair Rebate credits the cost of a qualifying repair toward the new system. Check our current specials for tune-up offers.

When should you stop troubleshooting and call?

Stop and call right away if you smell gas, hear a carbon monoxide alarm, or see the same problem come back after you’ve reset it.

• You smell gas. Leave the house first. Lenoir City Utilities Board asks you to leave the premises before calling to report a leak, at 844-687-5282. In Farragut, where KUB supplies natural gas, call KUB’s 24-hour emergency line at 865-524-2911 once you’re outside.
• A carbon monoxide alarm sounds. LCUB’s guidance is to leave immediately and call 911.
• The breaker trips again after one reset.
• A burning smell lasts past the first few minutes of the season’s first run.
• The burners keep lighting and shutting off, or the furnace keeps stopping and restarting.
• There’s water around the furnace or soot near the vent pipe.

Eco Home Solutions provides same-day heating repair with 24/7 emergency response across Lenoir City, Farragut, Tellico Village, Loudon and Knoxville. If your outdoor unit is the problem, we handle heat pump repair too.

Should you repair or replace a furnace that keeps failing?

Replacing a furnace often makes more sense once it’s past 15 years old or a repair approaches half the cost of a new system. Carrier says a well-maintained gas furnace should last 15 or more years. Eco’s repair or replace calculator applies the same rules our technicians use: the 50% rule, and the $5,000 rule, where you multiply the system’s age by the repair cost. If the answer is replace, our heat pump vs. gas furnace guide compares installed costs and TVA rebates for Lenoir City and Farragut homes.

Frequently Asked Questions

Why does my furnace blow cold air and then hot air?

That’s usually normal. Carrier says many furnaces wait 30 to 60 seconds after the burners light before starting the blower, and the first air out has been sitting in cold ductwork. If it stays cold for more than a few minutes, work through the checks above.

Is it dangerous if my furnace is blowing cold air?

Usually not on its own. It’s most often a thermostat setting, a filter, or a safety switch doing its job. If you smell gas or a carbon monoxide alarm sounds, leave the house and call from outside. If you see soot around the furnace, turn it off and call for service.

Why is my heat pump blowing cold air in winter?

A heat pump’s air runs about 90°F to 110°F at the vent, cooler than a furnace’s, so it can feel cool while working normally. It also blows cooler air briefly during defrost. If the air stays cold, the outdoor unit is iced over, or only emergency heat keeps up, it needs service. See our heat pump winter guide.

Still no heat?

If the checks above didn’t bring the heat back, we’ll find the cause, explain it, and give you the price before we start. Call (844) 305-4822 or schedule a heating repair. Eco Home Solutions is a Carrier Certified Dealer with NATE-certified technicians, licensed in Tennessee (HVAC #81014), and we answer 24/7.