Your furnace doesn't get as much attention as your AC in Texas — and that's exactly why problems sneak up on homeowners. DFW winters are short but they're real: we hit 30-40°F regularly, with freeze events that drop into the teens. After February 2021 proved that Texas heating systems matter, I've made furnace inspection a bigger part of every fall tune-up. Here are 5 signs your furnace needs professional attention before the next cold snap.
As an EPA 608 Universal certified technician working under Frosty's TDLR Texas License TACLA126718E, I've condemned more cracked heat exchangers than I can count in 8 years — and I've never repaired one. Last November I ran a combustion analyzer on a 22-year-old furnace in a Valley View home in Farmers Branch and measured 180 ppm of carbon monoxide spilling into the return air. The homeowners, a retired couple, had been waking up with headaches for weeks. We shut down the furnace that night, brought them portable electric heaters, and replaced the system the following Monday. A cracked heat exchanger isn't a repair discussion — it's a safety call, every single time. More on our credentials and safety standards on our about page.
What Does It Mean When Your Furnace Makes Banging or Booming Noises?
A banging sound when your furnace kicks on usually means delayed ignition — gas is building up in the combustion chamber before igniting, creating a small explosion. This is a serious safety issue that needs immediate attention.
Common causes:
- Dirty burners: Carbon buildup blocks even gas flow — cleaning is usually part of a tune-up ($150, Member: $127.50)
- Failing ignitor: $350-$500 (Member: $297.50-$425) — the ignitor doesn't light the gas fast enough
- Gas valve issue: $500-$800 (Member: $425-$680) — improper gas flow timing
Don't ignore furnace banging. Every delayed ignition stresses the heat exchanger — the component that separates combustion gases from your home's air supply. Repeated stress cracks the heat exchanger, and a cracked heat exchanger means full furnace replacement. We never repair heat exchangers because the carbon monoxide risk is too high.
Why Is My Furnace Blowing Cold Air?
A furnace blowing cold air means the burners aren't firing or the system is overheating and shutting down as a safety measure. The furnace fan continues running (pushing unheated air through the vents) even after the burners shut off.
Most common causes in DFW:
- Dirty filter causing overheating: Replace the filter first — this is free to check. A clogged filter restricts airflow, the heat exchanger overheats, and the high-limit switch kills the burners to prevent cracking.
- Failed ignitor: $350-$500 (Member: $297.50-$425) — the most common furnace repair I do. The ignitor glows white-hot to light the gas. They're rated for about 3-5 years but DFW's power fluctuations from the ERCOT grid can shorten that.
- Flame sensor malfunction: $250-$400 (Member: $212.50-$340) — the sensor can't detect the flame and shuts the gas valve as a safety precaution.
If your furnace starts, runs for 2-3 minutes, then shuts off and blows cold air — that's the high-limit switch cycling. It's trying to protect the heat exchanger. Get this diagnosed before you end up needing a full replacement.
Related: Why Your Furnace Keeps Turning On and Off (Short Cycling).
Can a Strange Smell From My Furnace Be Dangerous?
Some furnace smells are normal, others are dangerous. A burning dust smell when you first turn on the furnace in fall is normal — that's accumulated dust burning off the heat exchanger. It should go away within 30-60 minutes.
Smells that need immediate attention:
- Rotten eggs / sulfur: This is the mercaptan additive in natural gas. You have a gas leak. Turn off the furnace, open windows, leave the house, and call your gas company (Atmos Energy in DFW) before calling us.
- Electrical burning smell: A motor or wiring is overheating — turn the system off and call for diagnosis. Could be a failing blower motor — our complete blower motor repair service (diagnosis, parts, labor, testing, and our guarantee) runs $750-$1,500 all-inclusive ($637.50-$1,275 for Frosty Club members).
- Metallic smell: This can indicate a cracked heat exchanger — combustion gases entering your air supply. Turn off the furnace and call immediately. CO detectors should be on every floor.
I cannot stress this enough: if you smell gas, get out of the house first. Call 911 or Atmos Energy from outside. Don't flip light switches, don't use your phone inside, don't start your car in the garage.
Why Does My Furnace Keep Turning On and Off?
Short cycling in a furnace — running for a few minutes, shutting off, restarting — means something is triggering the safety controls. Your furnace is designed to shut down when it detects unsafe conditions, and short cycling means it keeps finding a reason to stop.
Common causes:
- Dirty filter — restricted airflow causes overheating (free fix — check the filter)
- Faulty thermostat — sending erratic signals. Basic replacement: $350 (Member: $297.50)
- Bad flame sensor — $250-$400 (Member: $212.50-$340)
- Oversized furnace — heats too fast, shuts off, house cools, cycles again. This was more common in older Irving and Lewisville homes where contractors oversized equipment.
Short cycling wastes gas, drives up bills, and puts repetitive thermal stress on the heat exchanger. Each on-off cycle expands and contracts the metal, eventually causing cracks.
Related: Why Your Furnace Blows Cold Air: 7 Common Causes.
How Do I Know If My Heat Exchanger Is Cracked?
A cracked heat exchanger is the one furnace problem that always means replacement — never repair. The heat exchanger separates combustion gases (including carbon monoxide) from the air your family breathes. A crack allows those gases to mix.
Warning signs of a cracked heat exchanger:
- Visible soot or carbon buildup inside the furnace
- Yellow or flickering burner flame (should be steady blue)
- Metallic or aldehyde smell when the furnace runs
- CO detectors alarming
- Family members experiencing headaches, nausea, or dizziness when the furnace runs
According to the EPA, carbon monoxide is responsible for over 400 deaths annually in the U.S. and over 20,000 emergency room visits. A cracked heat exchanger is one of the primary sources of residential CO exposure.
If you suspect a cracked heat exchanger, turn off the furnace immediately and call (469) 254-0548. We'll diagnose it with our combustion analyzer and camera inspection. If it's cracked, we'll discuss full system replacement — new systems range from $8,000-$20,000+ and include modern safety features. Check our AC Replacement Cost Calculator for pricing (it covers full HVAC systems, not just AC).
When Should You Schedule a Furnace Inspection?
The best time to inspect your furnace in DFW is September through October — before the first cold snap but after the summer AC season winds down. A fall tune-up ($150, Member: $127.50) checks all safety controls, tests the heat exchanger, and catches problems while there's still time to repair or replace before you need heat.
Frosty Club Premium members ($300/yr) get 2 tune-ups included — spring AC and fall heating. That's the easiest way to stay on top of both systems.
Call (469) 254-0548 or request service online.
We serve homeowners in Farmers Branch, Coppell, Irving, Flower Mound, Lewisville, and Grapevine. All technicians are EPA 608 certified and licensed under TDLR TACLA126718E.
Related Articles
- Why Your Furnace Keeps Turning On and Off (Short Cycling)
- Why Your Furnace Blows Cold Air: 7 Common Causes
- Pilot Light Won't Stay Lit? 5 Common Causes and Fixes
Written by Omar Jacobo, EPA 608 Universal Certified Lead Technician at Frosty's HVAC LLC. Family-owned since 2018, 99 Google reviews at 4.9 stars, Texas License TACLA126718E. Serving DFW homeowners with flat-rate pricing and no surprises.
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