Why Is My Furnace Blowing Cold Air?

Furnace Blowing Cold Air

A furnace blowing cold air is the last thing you want to deal with, especially on a freezing winter day in Brampton!

The good news is that there is help available for your furnace problem. Our expert, Brendan Aldridge at Dr HVAC, provides us with some insight on these issues. Check out his 10 solutions for a furnace blowing cold air.

Trane Furnace xt95

1. Incorrect Thermostat Setting

You thought you set the thermostat to a comfortable temperature. However, sometimes you’re warm and other times you feel the vents blowing cold air. Double-check the thermostat. It may be set to ON, which means that the fan will run all the time, even when the furnace is cycling off.

SOLUTION: Start by checking your thermostat settings. Ensure it’s set to “Heat” mode and the temperature is set higher than the current room temperature. If you have a programmable thermostat, double-check the schedule to make sure it’s programmed correctly. If you have a smart thermostat, ensure it’s connected to your Wi-Fi network and properly configured.

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If you have an older thermostat with a mercury switch, ensure it’s level and hasn’t been bumped out of position. Consider upgrading to a digital or smart thermostat for more precise temperature control and energy efficiency.

2. Low Battery Thermostat

Your thermostat may be causing trouble for other reasons. 1) If it is battery powered, the battery may have run down. OR 2) If you just installed a new thermostat yourself, you might have purchased a type that doesn’t work with your system.

SOLUTION: If you’re still experiencing problems after checking the thermostat settings, there may be other issues with your heating system. Verify that the thermostat is receiving power and that the display is functioning properly. Check for loose or corroded wires and tighten any connections. If your thermostat uses batteries, replace them to ensure reliable operation.

For more complex thermostat issues, it’s advisable to consult a Dr HVAC technician. They can diagnose and resolve wiring or control board problems that may be affecting your thermostat’s performance.

3. Dirty Air Filter

Is your furnace frequently shutting on and off? Your air filter may have become clogged. When airflow to a gas furnace is restricted due to a blocked air filter, the safety switch will eventually shut off the burners. Since no hot air is being produced, your heater blowing cold air is the result.

SOLUTION: A clogged filter restricts airflow, reducing the efficiency of your furnace and potentially causing it to blow cold air. Replace the dirty air filter with a clean one. Consider using high-quality, pleated filters that capture more particles and promote better airflow. Make a habit of checking and replacing the filter regularly, typically every 1 to 3 months, to keep your furnace running efficiently. (Find out how often to change your furnace filter.)

4. Clogged Condensate Line

As a byproduct of their function, high-efficiency furnaces produce condensed liquid. This condensate normally drains harmlessly away. Occasionally, though, the condensate drain line clogs up, resulting in a furnace blowing cold air and leaking water.

SOLUTION: The condensate line drains moisture produced during the heating process. If it becomes clogged, it can lead to furnace malfunctions, including the production of cold air. Locate the condensate line and inspect it for blockages or debris. Gently clear any obstructions using a long, flexible brush or a mixture of equal parts water and vinegar. Consider scheduling annual maintenance with a professional technician to ensure the condensate line remains clear.

5. Pilot Light Is Out

Your gas furnaces’ pilot lights may be out for one of two reasons. Either it has simply blown out, or it is not lighting correctly in the first place. The latter problem may be due to blockage from dirt and soot, or a malfunctioning thermocouple. If there’s no gas, there’s no heat, and your furnace will be blowing cold air instead of blowing hot air.

SOLUTION: If you have a gas furnace with a pilot light, it may have gone out, preventing the furnace from producing heat. Refer to your furnace’s manual for instructions on relighting the pilot light. If you’re unsure or uncomfortable doing this yourself, contact a professional technician to safely relight the pilot light and inspect for any underlying issues.

6. Insufficient Gas Supply

Obviously, a gas furnace needs an adequate supply of natural gas to work properly. Was your gas supply turned off for any reason? Is your gas valve closed? If the answer to both questions is negative, a blocked gas supply pipe could be interfering with the flow of gas.

SOLUTION: A lack of gas supply can hinder the furnace’s ability to produce heat. Check other gas appliances in your home, such as stoves or water heaters, to see if they’re working. If not, there may be a broader gas supply issue in your area, and you should contact your gas provider. If other gas appliances are working fine, the problem may lie with your furnace’s gas supply line. In this case, find a furnace repair expert to inspect and fix the gas line.

7. Leaky Ducts

Older ductwork tends to develop cracks and leaks as a result of wear and tear. Even though the system is actually blowing warm air, heat is leaking out before it ever reaches you, so you end up feeling as if your furnace is blowing cold air.

SOLUTION: Begin by conducting a thorough inspection of your air ducts. For small gaps or cracks, consider using mastic, a specialized sealant designed for ductwork. If you have metal ductwork, opt for foil tape designed specifically for HVAC applications. Regular maintenance, including periodic duct inspections, should be part of your routine HVAC care. By addressing leaks promptly, you can enhance your system’s efficiency, improve indoor air quality, and reduce energy costs. 

For more extensive or hard-to-reach leaks, it’s advisable to consult a Dr HVAC technician. They have the expertise and specialized tools to conduct a thorough duct inspection and employ advanced sealing techniques. 

8. Dirty Flame Protector

A dirty flame protector, also known as a flame sensor, is a safety feature in your furnace that detects the presence of a flame. Over time, it can accumulate grime and soot, causing it to malfunction. When this happens, the furnace may shut off the gas supply, resulting in cold air blowing through the vents.

SOLUTION: Cleaning the flame protector is a relatively straightforward task. Start by turning off the furnace’s power and then carefully remove the flame sensor. Gently clean it using a fine-grit emery cloth or steel wool. Once it’s free from debris, reattach it and restore power to the furnace. Regular maintenance, including cleaning the flame protector, can help prevent this issue from recurring.

9.  Cracked Heat Exchanger

The heat exchanger is a crucial component that transfers heat from the burner to the air that circulates through your home. Over time, it can develop cracks due to the expansion and contraction caused by repeated heating and cooling cycles. A cracked heat exchanger can lead to a variety of problems, including the circulation of cold air.

SOLUTION: Unfortunately, a cracked heat exchanger is a serious issue that requires professional attention. It’s essential to have a Dr HVAC technician inspect and, if necessary, replace the heat exchanger. Ignoring this problem can lead to safety hazards, as it can allow carbon monoxide to leak into your home.

10. Overheated Furnace

Furnaces have safety mechanisms in place to prevent overheating. If one of these systems detects that the furnace is reaching dangerous temperatures, it will shut off the burner to prevent damage. When this happens, the air blowing from the vents may feel cold.

SOLUTION: To address an overheated furnace, start by turning off the power to the unit and allowing it to cool down. Check the air filter and make sure it’s clean and not obstructing airflow. If the issue persists, it’s best to consult a professional technician. They can inspect the furnace for any underlying problems and ensure that all safety features are functioning correctly. Regular maintenance, including changing the air filter, can help prevent overheating in the future.

Stay Comfortably Warm This Winter

Rely on Dr HVAC for furnace maintenance and repair by our fast, efficient and friendly experts. We care about your home comfort.



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