After months of sitting idle, most furnaces that blow cold air usually have a small hiccup.
First, Give It 2 Minutes
A brief cool breeze at startup is normal. Cold air that keeps coming is a problem.
A gas furnace runs a startup sequence.
The inducer fan clears the flue, the igniter heats, the burners light, and then the blower kicks on. Air feels cool for 60 to 90 seconds while the heat exchanger warms up.
That’s the metal chamber that heats your air without mixing in combustion gases.
The 5 Usual Suspects
We see these every September/October from Frenchtown to Lolo:
- The thermostat is set to COOL, or fan set to ON. ON runs the blower constantly, even between heat cycles. Switch to HEAT and AUTO.
- Dirty flame sensor. This thin rod confirms the burners lit. Summer dust coats it, the furnace can’t see the flame, and it shuts the gas off.
- Clogged filter. Choked airflow trips the limit switch, a safety that kills the burners when temperatures climb too high.
- Blocked condensate line. High efficiency units drain water through a small tube. Algae plugs it over summer, and a pressure switch locks the burners out.
- The gas valve closed. Somebody shut it during a summer project.
Triage Chart
What you notice | Likely cause | Your move |
Cold nonstop, no burner sound | Thermostat or gas valve | Check settings and valve |
Warm briefly, then cold | Flame sensor or limit switch | Swap filter, then call us |
Clicking, no flame | Igniter or pressure switch | Call us |
Water pooling near furnace | Condensate clog | Call us |
Rotten egg smell | Possible gas leak | Leave home, call NorthWestern Energy |
Why September Is the Smart Time for Missoula
The U.S. Energy Information Administration raised its winter heating cost forecasts last December after NOAA signaled colder weather. Natural gas and propane led the increase.
EIA also projected that 2026 wholesale natural gas prices would run roughly 16% above 2025. A dusty, struggling furnace burns more of that pricier fuel.
Missoula has plenty of heating contractors, from national franchises to longtime local shops. Nearly all of us get buried the week the first cold front rolls into town.
Booking now beats the long November line.
What Sets Right Now Apart
Right Now Plumbing and Heating handles your furnace and your plumbing, so one trusted crew covers the whole house.
We work in Grant Creek, the University District, Frenchtown, Linda Vista, the South Hills, Miller Creek, East Missoula, Lolo, and beyond.
A customer, Kathie, put it simply in a Google review recently, “They were able to find and fix the problem without telling us we needed a whole new system. We will definitely be calling them in the future, if needed.”
Frequently Asked Questions
Why does my furnace blow cold air, then shut off?
Usually a dirty flame sensor or a tripped limit switch. Both cut the burners while the fan keeps going.
Is a burning smell normal on the first run?
Yes, for an hour or so while summer dust cooks off. A smell that lingers constitutes a call.
Can I clean the flame sensor myself?
Handy homeowners can, with the power off and fine steel wool. If you’re unsure, let a technician handle it.
How often should I change my furnace filter?
Every one to three months in the heating season is best practice.
How long do furnaces last in Missoula?
Most gas furnaces run 15 to 20 years with yearly maintenance.
Written by the owner of Right Now Plumbing and Heating.
Sources
- U.S. Energy Information Administration, “Colder winter weather increases our home heating expenditure forecasts,” Dec. 15, 2025: eia.gov/todayinenergy/detail.php?id=66864
- U.S. Energy Information Administration, STEO press release, Dec. 9, 2025: eia.gov/pressroom/releases/press581.php
- Right Now Plumbing and Heating (Missoula), Google Business Profile review by Jake Harris, March 24, 2026