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Why your furnace is blowing cold air, and what to check
Cold air from the registers is one of the most common winter calls we get. Sometimes it is a thermostat setting. Sometimes it is a part. Here is how to tell the difference in about ten minutes.
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NBy Nell Bradshaw, HVAC Guides Editor · Updated September 2026
Quick answerA furnace blowing cold air in Spokane most often has the thermostat fan set to On, a clogged filter tripping the high-limit switch, snow blocking the plastic vent pipes, or a dirty flame sensor that shuts the burners off seconds after lighting. The first three you can check yourself; a sensor or ignition fault needs a technician.
Check the thermostat fan setting
If the thermostat fan is set to On rather than Auto, the blower runs all the time, including between heating cycles, and the air feels cool. Switch it to Auto and see whether the cold air stops between cycles. If it does, nothing is broken.
Look at the filter
A clogged filter starves the furnace of air, the heat exchanger overheats, and the high-limit switch shuts the burners off while the blower keeps running to cool it down. That feels exactly like cold air. Replace the filter, wait a few minutes and try again. If it happens repeatedly, the limit switch or blower may also need attention.
Clear the vent pipes outside
High-efficiency furnaces vent through two plastic pipes on the side of the house. Spokane gets most of its precipitation as winter snow, and drifts or roof slides can bury those pipes. The pressure switch then stops the burners from lighting. Clear snow and ice from both pipes, then turn the furnace off and on at the switch.
Still blowing cold after the basic checks?
Call (509) 404-0016Faults that need a technician
If those checks do not fix it, the furnace is probably stopping partway through its start sequence:
- Dirty flame sensor: the burners light, then shut off within seconds.
- Failed ignitor: you hear the inducer, but nothing lights.
- Stuck pressure switch or a blocked condensate trap.
- Gas valve or gas supply problem.
- Control board fault, often shown by a blinking code.
Read the blinking light
Most modern furnaces have a small light on the control board, visible through a window in the lower panel. The number of blinks is a code, and the chart is usually printed inside the door. Write it down before you reset power, because resetting clears it, and give it to the technician. It saves diagnostic time.
Our furnace repair visits start by reading that code and testing the part it points to. If it is night and the house is cooling fast, see what to do when the heat quits at night.
Heat pump homes are different
If your home has a heat pump rather than a furnace, cool air is sometimes normal. During a defrost cycle the heat pump reverses for a few minutes to melt frost from the outdoor coil, and the air from the registers can feel cool until the backup heat catches up. Heat pump supply air is also cooler than furnace air even when it is working well, often feeling lukewarm to the hand.
What is not normal is cool air for long stretches, a unit covered in solid ice or backup heat running all the time. Our guide to a heat pump icing up in winter covers those.
Preventing it next winter
Most cold-air calls trace back to a filter, a dirty sensor or a vent problem, all of which a fall furnace tune-up catches before the first freeze. Change filters on schedule, keep the vent pipes clear after storms, and have the sensor cleaned once a year.
More Spokane heating and cooling guides
Cold air questions
Is it safe to keep resetting my furnace?
Once or twice is fine. If it keeps locking out, stop and call, because the safety is tripping for a reason.
Can I clean the flame sensor myself?
It is possible, but it involves opening the burner compartment. Most homeowners are better served by a technician.
Why does it blow cold only at the start?
A short burst of cool air before the heat arrives is normal on some furnaces.
Could it be the gas?
Yes, if other gas appliances also fail. Call the gas utility if you smell gas.
Will a tune-up prevent this?
It prevents most causes by cleaning the sensor and checking vents and switches.
Furnace still blowing cold?
Call any hour for furnace repair in Spokane, WA.
