During the winter, the last thing you want is cold air coming from your vents. If it’s the dead of winter, yet your furnace is blowing cold air, you could have a problem.
We’re going to highlight several common causes and how to prevent cold air from your furnace during winter so you can stay comfortable and cozy.
Thermostat
The first thing you should check if you have cold air coming from your vents during winter is your thermostat. Sometimes, your thermostat may be set to Fan Only instead of Heat.
When the fan setting is turned on, the system will continuously circulate air through your vents, even when the furnace is not heating. If this is the case, the air coming from the vents may feel cooler than your desired temperature.
To fix this, ensure your thermostat is set to Heat, and the fan setting is set to AUTO instead of ON. When AUTO is on, the fan should only blow when the furnace is actively heating the air. This should fix the issue of cold air coming from the vents.
Ignition Issues
If your heater is not lighting the fuel properly, the air from your vents may feel cold. Modern furnaces use an ignition system to ignite the gas that produces heat. If the ignition component is worn or fails, the furnace may still run the fan but won’t generate warm air.
The most common issues include a faulty electronic igniter, a dirty or worn pilot light assembly, or issues with the gas supply. When these issues occur, the blower may still push air through the ducts without warming it first.
If you suspect an issue with ignition, it’s best to contact an HVAC professional for furnace repair. The technician will test the ignition, replace worn or broken parts, and ensure your system is operating efficiently.
Dirty Flame Sensor
A dirty flame sensor is another common cause of cold air coming from your furnace during winter. A flame sensor’s job is to detect whether the gas burner has successfully ignited. If the sensor can’t detect a flame, the system automatically shuts off the gas as a safety precaution.
A dirty flame sensor causes your furnace to turn off quickly after starting. The furnace may start to heat but then shut off. This results in very little warm air reaching your air vents. This issue can typically be resolved by cleaning or replacing the flame sensor. Contact an HVAC technician to inspect and replace the sensor.
No Fuel
Low or no fuel can also cause the furnace to blow cold air. Furnaces require a steady supply of fuel to generate heat. Whether it's propane, natural gas, or heating oil, it needs some kind of fuel to operate. So, if the fuel supply is interrupted or runs out completely, the system won’t be able to heat the air.
The air may still circulate through the vents though, which is why you’ll feel cold air coming into your home. This can happen if a gas valve is accidentally turned off or there is a disruption in the fuel supply line.
If you think there may be a fuel supply issue, check the fuel source and contact an HVAC professional if the issue persists.
Ductwork Issues
Sometimes, cold air from crawlspaces or attics can get into ducts if they have leaks, gaps, or poor insulation. When this happens, the warm air produced by your furnace mixes with the cold air before reaching your vents. This can make your home feel colder than it should, even when your furnace is running.
Poorly sealed or damaged ductwork reduces heating efficiency and forces your system to work harder to maintain the desired temperature. It’s important to seal duct leaks and ensure they’re properly insulated to prevent cold air from getting in.
Clogged Drain Lines
High-efficiency furnaces produce condensation during the heating process, and moisture is released through a condensate drain line. When this drain line becomes clogged with dirt, dust, or algae, the furnace may trigger a safety switch to shut off the burners. The blower may still run, but the burners won’t ignite, meaning the air will be lukewarm at best.
Call an HVAC professional to clear your clogged drain line to restore normal furnace operation. Regular furnace maintenance can help prevent blockages and help your furnace run efficiently all winter long.
Schedule a Furnace Inspection
If you still aren’t sure why cold air is coming from your AC vents in winter, contact Mercurio’s today. Mercurio’s is Tacoma, WA’s heating and air conditioning authority. Our professionals are highly skilled at diagnosing and repairing furnace issues.
If you need heating repairs or maintenance, our team can handle it. Contact us today to schedule an appointment.
