Why a Furnace or Heat Pump is Blowing Cold Air
Date: December 27, 2019
Is Your Furnace/Heat Pump Acting Like an AC Unit and Blowing Cold Air?
The Phoenix weather is getting “cold,” and a furnace or heat pump blowing cold air is the last thing Arizonans want when we come home. Furnaces and heat pumps that blow cold air will be doing so for entirely different reasons due to each unit’s method of heating the air. Furnaces use gas, and heat pumps use electricity to generate heat.
What Causes a Furnace to Blow Cold Air?
A furnace that is blowing cold air is most likely due to one of four possible causes:
- Your thermostat is set to “ON”
- The pilot light is out
- The furnace has overheated
- Gas is not being supplied to the unit
The Thermostat is Set to “ON”
If you notice your furnace is blowing hot air some of the time and cold the rest of the time, your fan is most likely set to “ON” when the correct setting would be “AUTO.” When the thermostat is set to “ON,” the fan will be blowing non-stop, even when the furnace burners are not running. This setting means the furnace is continuously working on blowing air into your home, even when the air is not being heated, wasting energy and money.
The simple solution to this problem is switching the thermostat into the “AUTO” position. If this does not fix the problem and your furnace keeps running continuously, there is another issue with your HVAC that a professional will need to solve.
The Pilot Light is Out
Older furnaces use a permanent pilot light to ignite the gas for the burner. When the pilot light goes out, the furnace unit has no way to heat the air. There should be instructions on your furnace to show how to relight the pilot light. If the pilot light continues to go out, you have another issue that will require a professional to solve.
As an additional note, old furnaces waste tons of gas to keep the pilot light lit. Consider upgrading to a newer, more efficient furnace that doesn’t use a pilot light, or switch to a heat pump.
Your furnace uses a group of metal coils called the heat exchanger to heat the air. When air blows over these coils, it picks up this heat. The heat exchanger can get too hot and overheat. Your furnace system is designed to sense any overheating and will turn off the burners but keep the fan blowing to help cool down the heat exchanger. If this is happening to you, you will notice cold air coming from your vents and possibly even a burning smell and slight humming noise.
A variety of issues could cause a furnace to overheat. Still, the most common is a blockage or restricted airflow. We suggest checking your air filter and making sure it is clean. If you replace your air filter and continue to notice the same problems, it’s time to have a professional examine the situation.
No Gas Supply to the Unit
A furnace needs a constant supply of gas to the burners to provide heat to your home. If the gas supply is weak or cut off completely, the pilot light will be unable to stay lit, and cold air will blow from the furnace. Make sure the gas valve is turned on. If that doesn’t help, guess what time it is? Time to call your Donley Service Comfort Heroes!
What Causes a Heat Pump to Blow Cold Air?
If your home uses a heat pump and you notice the vents are blowing cold air, there are three likely scenarios to explain why:
- The pump isn’t blowing cold air
- The pump is set to “defrost mode”
- Something is wrong with the unit
It Just Feels Like Cold Air is Blowing
Heat pumps move heat from the outdoor air into your home. As the outdoor temperature drops, the pump cannot pull as much heat from the air. For example, say the outside temperature drops to 20 degrees (In Phoenix? Unlikely, but it can happen.). The heated air blowing from your heat pump would likely be around 85-90 degrees. Since the average body temperature is 98.6 degrees, it feels deceptively cold.
Don’t worry, if the heat pump is unable to keep up with the outside air, it will automatically switch to backup electric coils.
The Heat Pump May be Set to “Defrost Mode”
While in heating mode, the heat pump’s outdoor coils are vulnerable to freezing over, so it will automatically switch to defrost mode to protect the coils. This cycle should only last for a few minutes, but you can check this by checking to see if steam is coming from the heat pump. If there is no steam, your heat pump is in defrost mode.
Something is Wrong With Your Heat Pump
When a heat pump is blowing cold air for more than a few minutes, the unit may be experiencing problems that an HVAC professional will need to identify. These could include a refrigerant leak, a bad reversing valve, faulty components, or your heat pump is losing efficiency due to age. Refrigerant leaks and faulty reversing valves are complicated and dangerous, and the EPA requires a certified professional to handle the job. When the components of the heat pump fail to perform or perform inefficiently, the system needs regular servicing, which is recommended at least once a year.
If you continue to encounter issues with your furnace or heat pump, schedule a service today with a Donley Service professional, so you and your family stay warm this winter.