Furnace is Blowing Cold Air Instead of Heat

Quick answer

If your furnace is blowing cold air, first check the thermostat settings and air filter. If those are fine, turn off the power and inspect the pilot light or ignition system. Replace the filter if dirty, and call a professional if the problem persists.

Confirm the symptom

• Furnace fan is running but not producing heat
• Thermostat is set to heat but no warm air is coming out
• Air from vents feels cold or barely warm
• Furnace makes normal noise but no heat output
• Heat works briefly then stops

Tools and prep

• Screwdriver set
• Flashlight
• Replacement air filter
• Thermometer (optional)
• Safety gloves
• Turn off furnace power at the circuit breaker
• Check for gas supply if applicable

Step-by-step troubleshooting

1. Check Thermostat Settings
   Do: Verify the thermostat is set to 'Heat' and the desired temperature is higher than the current room temperature.
   Observe: Thermostat is in correct mode and set appropriately.
   Means: Thermostat is not the issue if settings are correct.
   Next: Check Air Filter
2. Check Air Filter
   Do: Locate and inspect the air filter. Replace it if it is dirty or clogged.
   Observe: Clean air filter or newly installed filter.
   Means: A dirty filter can restrict airflow and cause heating issues.
   Next: Check Pilot Light or Ignition System
3. Check Pilot Light or Ignition System
   Do: Look at the pilot light or ignition system. If it's out, relight it following the manufacturer's instructions.
   Observe: Pilot light is lit or ignition system is functioning.
   Means: A failed pilot light or ignition can prevent the furnace from heating.
   Next: Check Gas Supply
4. Check Gas Supply
   Do: Ensure the gas valve is open and there is no gas leak. If you smell gas, turn off the furnace and call a professional immediately.
   Observe: Gas valve is open and no gas smell is detected.
   Means: A closed gas valve or leak can prevent the furnace from heating.
   Next: Inspect Blower Motor
5. Inspect Blower Motor
   Do: Check if the blower motor is running but the burners are not igniting. This may indicate an electrical or control issue.
   Observe: Blower motor runs without heat production.
   Means: The issue may be with the burners or control board.
   Next: Call a Professional
6. Call a Professional
   Do: If the issue persists after checking all components, contact a licensed HVAC technician for further diagnosis and repair.
   Observe: Professional diagnosis and repair.
   Means: Complex issues require expert assistance.
   Next: End

Common causes

Parts matching

Common parts needed for a furnace blowing cold air:

• Air Filter
• Thermostat
• Ignition Kit
• Gas Valve
• Ignition Control Module
• Thermal Switch
• Control Board

Always refer to your furnace's manual for part compatibility and installation instructions.

When to call a professional

• If you smell gas or suspect a gas leak
• If the pilot light won't stay lit after multiple attempts
• If the furnace makes unusual noises or smells while running
• If the blower motor runs continuously without heat production
• If you're unsure about any step or lack the necessary tools
• If the issue persists after trying all troubleshooting steps

FAQ

Related guides

• furnace not producing heat
• furnace blowing cold air
• furnace not igniting

Related searches: furnace not heating properly, furnace pilot light not working, furnace thermostat issues, furnace gas supply problems, furnace blower motor problems, furnace filter replacement, furnace ignition system failure, furnace control board issues, furnace thermal switch failure