Furnace Blowing Out Cold Air

Quick answer

If your furnace is blowing cold air, first check the thermostat settings and air filter. Ensure the gas supply is on and the circuit breaker hasn't tripped. If these don't resolve the issue, the blower motor or heat exchanger may need professional attention.

Confirm the symptom

• Furnace is running but blowing cold air
• Thermostat is set to heat
• No hot air after furnace runs for several minutes
• No unusual error codes on thermostat or furnace display

Tools and prep

• Screwdriver set
• Flashlight
• New air filter (if needed)
• Thermometer (to check air temperature)
• Safety gloves and goggles
• Circuit breaker panel access

Step-by-step troubleshooting

1. Check Thermostat Settings
   Do: Verify the thermostat is set to 'Heat' and the desired temperature is higher than the room temperature.
   Observe: Thermostat is in 'Heat' mode and set correctly.
   Means: Thermostat settings are correct.
   Next: Proceed to next step.
2. Inspect Air Filter
   Do: Turn off the furnace power. Remove and inspect the air filter for dirt or blockage.
   Observe: Air filter is dirty or clogged.
   Means: A clogged filter restricts airflow and can cause cold air output.
   Next: Replace the air filter and restore power to test.
3. Check Gas Supply
   Do: Ensure the gas valve near the furnace is fully open. Check for any gas supply disruptions.
   Observe: Gas valve is closed or partially closed.
   Means: No gas supply prevents the furnace from heating the air.
   Next: Open the gas valve and wait for the furnace to ignite.
4. Inspect Circuit Breaker
   Do: Check the circuit breaker for the furnace in your electrical panel. Reset if tripped.
   Observe: Circuit breaker is tripped or shows signs of overload.
   Means: Electrical issues can prevent the furnace from operating properly.
   Next: Reset the breaker and test the furnace.
5. Test Blower Motor
   Do: Wait for the furnace to complete a heating cycle. Feel the air coming out of the vents after the cycle.
   Observe: Blower motor runs before the burners ignite or continues after the heat cycle ends.
   Means: Blower motor timing issues can cause cold air to blow.
   Next: Consult a professional HVAC technician for further inspection.
6. Check Heat Exchanger
   Do: Turn off the furnace and allow it to cool. Inspect the heat exchanger for cracks or damage.
   Observe: Visible cracks or damage in the heat exchanger.
   Means: A damaged heat exchanger can allow cold air to mix with heated air.
   Next: Contact a professional HVAC technician for repair or replacement.

Common causes

Parts matching

Common parts needed to fix a furnace blowing cold air include:

• Air Filter – Replace if dirty or clogged.
• Gas Valve – Ensure it is fully open and functioning.
• Blower Motor – Repair or replace if faulty.
• Thermostat – Verify it is set correctly and functioning properly.

Always turn off the furnace power before replacing parts to ensure safety.

When to call a professional

• Furnace continues to blow cold air after replacing the air filter and checking gas supply.
• You notice a burning smell or unusual noises from the furnace.
• The heat exchanger shows signs of cracks or damage.
• The furnace does not ignite or the burners do not light.
• You are unsure about handling electrical or gas components.
• The issue persists after following all troubleshooting steps.

FAQ

Related guides

• furnace not producing heat
• furnace blowing cold air instead of heat

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