Video: My Furnace is Blowing Cold Air: 8 Reasons & Ways to Fix
Figure 1: Replace furnace blower motor.
During the cold months, a furnace is your best friend, providing the warmth needed to keep your home comfortable.
However, discovering that your furnace is blowing cold air can be disconcerting.
Don't panic – there are several reasons why this might be happening, and many of them can be addressed with simple
solutions. In this guide, we'll explore the common causes behind a furnace blowing cold air and how to fix each
issue.
1. Common Causes and Solutions for a Furnace Blowing Cold Air
1.1 Pilot Light Failure
The pilot light is a crucial component in a gas furnace. If it goes out, the furnace won't produce heat. Reasons for
pilot light failure include a faulty thermocouple, gas supply issues, or simply a draft blowing it out. To address
this, follow these steps:
Solution:
Relight the pilot light according to your furnace's manual. If the pilot light won't stay lit or relight, it may be
time to replace the thermocouple or seek professional assistance.
Figure 2: Blue fire in a gas furnace.
1.2 Dirty Flame Detector/Sensor
The flame sensor ensures that the burners ignite and
remain lit. Over time, it can accumulate dirt or carbon buildup, leading to malfunction. When this happens, the
furnace may shut off the burners, causing it to blow cold air.
Solution:
Clean the flame sensor with a fine abrasive pad or emery cloth. If the problem persists, consider replacing the
sensor or consult a technician for a thorough inspection.
1.3 Insufficient Gas Supply
If there isn't enough gas reaching your furnace, it won't be able to generate the heat needed to warm your home. Gas
supply issues may include problems with the gas valve, a closed gas valve, or issues with the gas line.
Solution:
Ensure that the gas valve supplying your furnace is open. If it's closed, open it and check for gas leaks. If
problems persist, contact your gas utility provider or a qualified technician to assess and address the issue.
1.4 Dirty Air Filter
A clogged or dirty air filter restricts the airflow, causing the furnace to overheat and potentially blow cold air.
Solution:
Check and replace the air filter regularly, ideally every 1-3 months, or as recommended by your furnace
manufacturer. This simple maintenance task can significantly improve your furnace's efficiency and prevent cold air
issues.
Figure 3: Furnace filter.
1.5 Incorrect Thermostat Settings or Faulty Thermostat
Issues with the thermostat can lead to the furnace blowing cold air. Check if your thermostat is set to "Cool" mode,
"Fan" only mode, or a lower temperature, or if its wiring is shorted.
Solution:
1. Check Thermostat Settings: Ensure the thermostat is set to "Heat" mode and the desired temperature.
2. Inspect Wiring: Examine thermostat wiring for any damage. If found, replace or repair the wiring.
3. Replace Faulty Thermostat: If the thermostat is old or malfunctioning, consider replacing it with a new one.
1.6 Circuit Control Board Failure
The circuit control board is the brain of your furnace, coordinating various functions. If it fails, it may signal
the blower motor to run but fail to ignite the
burners, resulting in cold air circulation.
Solution:
Consult your furnace manual to locate the control board. Check for visible signs of damage or loose connections. If
the control board is faulty, replacement may be necessary. Seek professional help for accurate diagnosis and
repairs.
Figure 4: Install a new residential furnace.
1.7 Broken Ductwork
Cracks or gaps in the ductwork can allow hot air to escape before reaching your living spaces, leading to cold air
blowing out of the vents.
Solution:
Inspect Ductwork: Examine the ductwork for any visible damage. Seal any gaps or cracks with duct tape or hire a
professional for more extensive repairs.
1.8 Return Air Outlet Blocked
Blocked return air outlets hinder proper airflow, causing the furnace to struggle to distribute warm air
effectively.
Solution:
Ensure that your return air vents are unobstructed. Remove any furniture, curtains, or other items blocking the
vents. This simple step can improve airflow and enhance your furnace's heating efficiency.
2. FAQs about Furnace Heating
2.1 Where is the Blower Motor on a Furnace?
The blower motor in a furnace is typically located near the bottom of the furnace unit, below the heat exchanger. It
is part of the furnace's air handling system and is responsible for circulating air through the heating system.
The blower motor works in conjunction with the blower fan to
distribute warm air throughout the ductwork and into the living spaces of a home. Regular maintenance, such as
lubricating the motor and ensuring proper airflow, is essential for the efficient operation of the blower motor and
the overall performance of the heating system.
2.2 How to Change Blower Speed on Furnace?
To adjust the blower speed on a furnace, locate the blower motor's control board. Usually, it features multiple
terminals for various speeds labeled "Heat," "Cool," or "High," "Medium," "Low." Switch off the power, remove the
panel covering the control board, and refer to the furnace manual for specific instructions. Adjust the speed by
switching the wire to the appropriate terminal for the desired speed setting.
Alternatively, some newer models feature adjustable speed settings accessible through the control panel or with
specific switches or buttons. Always follow safety precautions and consult a professional if unsure.
Figure 5: Unscrew the furnace service panel.
2.3 How to Test Furnace Blower Motor?
To test a furnace blower motor, turn off the power, disconnect it, and visually inspect for damage. Use a multimeter
to check for continuity across the motor's windings. If there's no continuity, the motor may be faulty.
Additionally, check the capacitor for any visible damage.
If it's within the recommended capacitance range, it's likely functioning. You can also manually spin the blower
wheel; if it's stiff or doesn't spin freely, there may be an issue.
Always follow safety guidelines, and if you're uncertain or uncomfortable, consult a professional HVAC technician.
2.4 Why is My Furnace Running but Not Blowing Hot Air?
If your furnace is running but not blowing hot air, several reasons might cause this issue. These include a
malfunctioning thermostat, a clogged air filter, a faulty pilot light or flame sensor, restricted airflow due to
blocked vents or ducts, a malfunctioning blower motor, or issues with the gas supply.
Check the thermostat settings to ensure it's on heat mode and set to the desired temperature. Additionally, inspect
the air filter for blockages, ensure vents are unobstructed, and verify that the pilot light or flame sensor is
functioning correctly. If problems persist, seek professional HVAC assistance for a thorough inspection and repair.
Figure 6: Check a gas furnace.
3. Conclusion
A furnace blowing cold air can be a frustrating experience, especially during colder months. By understanding the
potential causes and following the suggested solutions, you can troubleshoot and resolve many issues on your own.
However, for complex problems or if you're unsure about the diagnosis, it's always wise to seek professional help to
ensure the safety and efficiency of your heating system. Regular maintenance and timely repairs will not only keep
your home warm but also extend the life of your furnace.
