Why Is My Furnace Always Blowing Cold Air?

This is a question we get asked frequently and there are many different reasons your furnace is blowing cold air. Here are the most frequently asked questions and answers to the different scenarios you could be experiencing.

Why does my furnace keeps running and blows cold air all the time even though it is not calling for heat
at my thermostat?

  1. The first thing to check is your Fan Setting at the thermostat. Most thermostats have a separate Fan Setting. The options should be ON, AUTO, or CIRCULATE. If your fan is set to ON or CIRCULATE, the furnace will continue to blow air even though the system is not calling for heat. Try changing this setting to AUTO instead and the fan will only run as the system calls for heating or cooling.
  2. If your Fan Setting at the thermostat is correct it could be that you have a fresh air timer installed. If your home was built in 1991 the Clark County and Vancouver area would fall under the Washington State Ventilation and Indoor Air Quality Code. These timers are located on the furnace and you can adjust the time that the fan turns off and on. There is also an option to turn the fresh air off at the timer itself. It is also possible that you have a whole home fresh air fan instead. These are located in the home usually in a hallway and have a separate switch or timer you can adjust as well. In Oregon including the Portland/Metro areas a similar code took place in April 2021 the ORSC Code. So if your home was built during this time you would have a fresh air system as well.

Why does it take several minutes after my furnace is done heating to stop blowing cold air?

  1. It could be that you have a dirty air filter. Because air flow is being restricted your furnace can overheat causing the system to turn off the burners and the heater fan will blow and emit out cold air. Try changing your filter and resetting your system.
  2. Dirty Burners can also be a culprit, it can cause the furnace to cycle and will default to the fan ON for safety. Because the fan is at the ON setting for safety you will feel air blowing continuously. A routine maintenance by a certified technician should be performed at a minimum once a year to resolve this issue.
  3. The Flame Sensor is another component that will malfunction if it is covered in dirt. The dirty flame sensor will also cause your furnace to cycle and the fan to stay ON as a safety feature. Keeping a clean filter will not allow as much debris to build up in these components along with your routine maintenance visits.
  4. Newer model gas furnaces have an electric ignition system. If this is not adjusted correctly it could cause your system to blow cold air.

Why do I feel cold air blowing while my furnace is heating?

  1. Newer variable speed furnaces technology allows for different blower speeds based on how much heat is needed to reach your desired temperature set at the thermostat. The air may feel cold coming directly out of the vent however, if the furnace is maintaining the temperature you have set on your thermostat then the furnace is working correctly. It will also depend on if you have a heat pump or just a gas furnace. Gas furnace heat is typically hotter than that of a heat pump. Older furnaces that do not have this technology may burn hotter and faster all the time but the energy wasted is very costly to the consumer and your home overall is not as comfortable.
  2. If you are feeling cold air while it is heating and the furnace is taking a very long time to heat up to the temperature set at your thermostat, it may be time to call an expert. The ignition system, burners or other components could be wearing out.

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