Why Is Cold Air Blowing When the Heat Is On?

Incorrect Thermostat Settings

One of the most common reasons for cold air blowing when the heat is on is simply a matter of an incorrect thermostat setting. Sometimes, a simple oversight can lead to an uncomfortable situation.

Ensure that your thermostat is set to “heat” rather than “cool.” If the furnace blower fan is set to “on” instead of “auto,” it will continue blowing cold air even when the furnace is not on to produce hot air. Also, check the temperature settings to make sure they are higher than the current room temperature.

Dirty Air Filters

The air filter plays a vital role in maintaining indoor air quality and the efficiency of your heating system. Over time, an air filter can become clogged with dust, debris, and other particles. A clogged filter restricts airflow, which can lead to a furnace blowing cold air in and of itself. If the furnace filter is dirty, it is possible that the furnace overheated as heated air can’t flow through the system. This triggers the high-limit switch, which is a safety feature that shuts down the heating cycle when the system overheats.

Regularly replacing a dirty air filter is essential for optimal furnace performance. Check the condition of the air filter monthly during the heating season, as heavy system use can result in a clogged air filter faster than usual. Commonly, a dirty air filter needs to be replaced every 1 to 3 months, depending on the type of furnace filter you use.

Issues with the Gas Valve

The gas valve controls the flow of natural gas to the burners. If the valve malfunctions, it can fail to open properly and prevent the burners from igniting and producing heat for the furnace’s heat exchanger, leaving you with a heater blowing cold air.

If you suspect an issue with the gas valve, refrain from attempting repairs yourself, as it involves working with potentially dangerous gas connections. Contact a professional technician to inspect and repair the valve.

Gas Supply Interruptions

Occasionally, disruptions in the gas supply can occur due to various reasons, including utility work, gas supply pipe leaks, or a faulty gas meter. If the gas supply is interrupted, your furnace won’t receive the necessary fuel to produce hot air, resulting in cold air being blown into your home.

If you experience your furnace blowing cold air instead of warm air, check with your utility provider to determine if there are any known gas supply interruptions in your area. If the problem persists, contact a professional to assess and address this furnace repair issue.

Pilot Light Issues

In an older gas furnace that blows cold air, it may mean an issue with the pilot light. If the pilot light goes out, there will be no flame to ignite the furnace burner once the valve opens, and the furnace won’t be able to start the heating process. Check the pilot light and follow manufacturer guidelines for relighting. If the problem persists, contact a professional HVAC technician to examine the pilot light assembly and make any necessary repairs.

Dirty Flame Sensor

A dirty flame sensor can also lead to a furnace blowing cold air when the heat is on, primarily in gas furnaces. The flame sensor is responsible for ensuring that the burners are lit and the furnace operates safely. If it’s covered in soot or dirt buildup, it may not detect the flame, causing the furnace to shut off or blow cold air. Cleaning the flame sensor is a delicate task best left to an HVAC professional.

Leaky Air Ducts

Leaking ducts can cause cold air infiltration, reducing the efficiency of your heating system. When your furnace is working, warm air is lost through these leaks in your air ducts. Cold air from unconditioned spaces can enter the system, mixing with heat and resulting in cool air. This makes it feel like the furnace is blowing cold air out of your vents, causing your home to feel chilly.

If you suspect leaky air ducts as the source of your furnace blowing cold air instead of warmth, call an HVAC professional to inspect your ducts and perform duct sealing. An HVAC system expert can identify and address any leaking ducts, preventing warm air from escaping and cold air from infiltrating, which saves you money and keeps your home supplied with hot air.

Is Your Furnace Blowing Cold Air? Call Atlas for Furnace Repair!

At Atlas Heating & Air Conditioning, we are here to help you keep your home warm and comfortable. If you’ve tried troubleshooting and are still faced with a furnace blowing cool air instead of blowing hot air, contact our experienced HVAC system technicians for reliable furnace repair services. Whether it’s a thermostat problem, dirty air filters, pilot light problems, mechanical failure, or ductwork leaks, we have the expertise to diagnose and resolve any heating system issue and get your furnace working properly once more.