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Why Is Cold Air Coming From Vents When Heat Is Off?

The heating system in your house may break and release cold air instead of hot air. This could be because an incorrect thermostat setting is keeping the air running despite turning it off. Alternatively, your heating system may malfunction because of a broken vent.

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A heating system in the house is necessary when it's cold, as it can heat the room and maintain a comfortable temperature. However, sometimes the heating systems can break down and release cold air instead.

When that happens, it will cost more money and waste electric energy. Therefore, you will have to fix it as soon as possible. So, here’s a complete guide for you when your vent is blowing cold air.

How To Fix Furnace Blowing Cold Air Coming From Vents

How To Fix Furnace Blowing Cold Air Coming From Vents

There could be multiple reasons for your furnace blowing cold air. I have gathered some possible reasons for that and how to fix it.

1. Cold Air Blowing Because Of Incorrect Thermostat

The thermostat in your home is a small device that is a crucial part of the heating or cooling system. This is because, with a press of a button, you can set the temperature range and comfortably stay warm.

So, when the furnace is blowing cold air from the vent, the first thing you should do is check the thermostat setting. As you do that, see if the device is set to "ON." If so, the problem could be because of that, as it keeps the fan running despite you turning the heat off. As such, simply change the setting from "ON" to "AUTO."

Once you do that, the fan will automatically turn off when the heat is turned off and will not blow cold air.

2. Broken Or Dirty Flame Sensor

Cold air can also blow because of a broken or dirty flame sensor located inside the furnace. The flame sensor is a device that detects flame and burns natural gas, maintaining the heating cycle. Moreover, when the device is broken or dirty, it can automatically turn the heat off so that natural gas does not leak into the house. Along with that, the fan could still blow cold air into the vent.

Accordingly, you will have to clean or replace the device. For that, I suggest calling a professional instead of trying your hand at it.

3. Issues With Ignition And Pilot Light

Another reason your furnace is blowing cold air could be due to a broken ignition system. In such a situation, the fuel in the heater will not ignite and will not be blowing hot air. Instead, it will release cold air only.

When that happens, check if the pilot light is on; if not, you will have to fix the device. If you want to do it yourself, you can use the manual that comes with the device and follow the instructions. When you are done, reignite and see if the flame goes out in a few minutes. If that happens, you might have a bigger problem, and you will need professional help.

Furthermore, if you cannot relight the pilot light, check the gas supply to see if it is a gas furnace. See if the gas valve is turned on; if it is, clean the gas valve properly for continuous supply.

Warning: When you relight the pilot switch, turn off the gas valve so that there are no leaks while you repair it. This is crucial because you can start an accidental fire with leaks and harm yourself.

4. Dirty Or Clogged HVAC Filter

The HVAC filter is an important part of your heating system. Since it helps in filtering dust particles, it maintains good air quality and keeps you healthy. However, it's a device that can get dirty and clogged and will need cleaning from time to time. Otherwise, the air will get blocked inside the furnace, and that can cause overheating, further leading the heater to auto-turn off.

With a dirty air filter, only cold air will come out of the air duct. An easy solution to this is to clean or replace the HVAC filter from time to time.

5. Low Refrigerant Charge In The AC System

A low refrigerant charge in the air conditioning systems can also be one reason cold air comes out of the vents. The cause of low refrigerant can be due to leaks in the coil or heat pump. Moreover, with low refrigerant, you will also lose the capacity and airflow of the heater. Whenever you realize that the first thing you can do is charge the refrigerant. If there is a leak in the heat pump system, call your HVAC expert to fix the leak.

6. Holes and Cracks In The Vents

The vents connected to your HVAC system direct warm air out of the air ducts. However, it can break and crack for several reasons, like rust, earthquakes, etc. If there are cracks in vents, it will draw cold air and feel like the furnace blowing cold air.

So, troubleshooting such a problem will require checking the vents, probably located in the attic, for cracks and holes. If you notice any crack, small or big, you will either have to patch it up or replace the whole section.

7. A Broken Compressor

The compressor of your heating system is located inside the heat pump, and it makes everything run smoothly. However, with time the compressor can break for several reasons. For instance, you could have over or undercharged it, or maybe there is a faulty motor. Moreover, it could be due to a dirty evaporator and coil or a faulty run capacitor.

When that happens, your heater will not work properly and impact the heating process.

8. A Broken Limit Switch Can Also Be The Problem

The limit switch is also another important device inside your heating system. Since the device automatically turns the burner off when the heat exchanger gets too hot, it is an important safety feature. However, it can malfunction and keep blowing hot air overheating the heat exchanger or turn the burner off continuously and stop the heating cycle.

9. Faulty or Broken Fan Or Motor

The blower fan and the inductor draft motor inside your gas furnace help in blowing hot air when it's in heating mode. The blower fan can malfunction when it is too old or has high static pressure. Moreover, it can go out because of inadequate ductwork. That’s when you can fix the problem by lowering the static pressure. If that does not work, you can replace the blower.

Besides, the inductor draft motor also works inside the furnace to remove exhaust gas. If the device gets faulty, the heater will push air that is filled with exhaust gas which is obviously dangerous for your health.

Now, the cause of a faulty draft motor could be due to a blocked flue pipe or some other restrictions. To fix the problem, you can try cleaning the blockage or restrictions or installing a new motor.

Why Is Cold Air Coming From Vents When Heat Is Off

Final Words

Educating yourself on the heating and cooling system in your home is important. I say this because it maintains the temperature of the room, keeping you comfortable. However, it can break and not work optimally.

When that happens, follow the instructions above, and you can fix the problem at the earliest. But, as furnace repair can be tricky, you will have to get professional help to diagnose and fix the problems.