Cold Air Blowing Out Of Vents When Heat Is On

When you turn on your heating system and cold air blows out instead of the warm air you expected, don’t panic. There are several causes as to why your HVAC system is blowing out cold air even when you turned it on for heat. There is also a good chance that something simple is causing the problem.
Listed below are three of the first things you should check when cold air is coming out of your vents even when you switch on the heat:


One of the most common reasons that your heating system is blowing out cold air is due to your thermostat. Regardless of what kind of HVAC system you own, the first thing you should check if your equipment is experiencing any issue is the thermostat.
When you turn on your system, wait for a few minutes. Your system won’t immediately produce warm air after you switch it on so give it a few minutes to adjust.

Set Temperature

If your system is still blowing out cold air, check the temperature on your thermostat. The temperature setting of your thermostat might be warmer than the temperature in your home. A simple solution to this is to turn up the heat.

Environment Temperature

The location where your thermostat is placed affects how it reacts. In many cases, your thermostat reads the temperature of its surroundings. Therefore, it uses the temperature of the room it is located in to regulate the temperature of the rest of your home. This can result in uneven air distribution and it can mean cold air blowing out your vents even when you turned the heat on.


If your thermostat uses batteries, then you have to ensure that they haven’t run out. Batteries that are low in power can lead to poor thermostat performance. As a result, your heating system might blow cold air when it shouldn’t.

Fan Switch

Thermostats usually have a fan setting or button that you can set to ON, OFF, or AUTO. Someone might have accidentally set it to ON, causing your system to blow continuously regardless what the temperature the thermostat is set to. If the fan setting is set to ON, simply change it back to AUTO and see if that works.

Broken Thermostat

There are times that a malfunctioning thermostat causes the issue. Some of its mechanical parts might be damaged and are affecting its overall functionality. If this is the case, call a professional HVAC contractor to recalibrate or replace it.

Electrical Panel

Your HVAC system runs on electricity. Check the breaker from inside your electrical panel. If the breaker tripped, then a multitude of issues can arise. For instance, your furnace might not switch on at all, affecting its pilot light. This can cause problems such as cold air blowing out of vents. A few of the reasons the breaker trips are:

  • Faulty wiring causing a short circuit
  • Overloaded circuits due to running too many electric appliances
  • Damaged wires and ground faults

You can try resetting the breaker to see if it will fix the issue. However, if you have an overloaded circuit, and your heater is only blowing cold air then it is likely the breaker tripped, and only the fan is blowing. If your HVAC system is what causes the breaker to trip, then don’t reset it. Have a professional take a look at your system instead. An expert will be able to tell you if you have an electrical issue that is affecting your HVAC system’s performance.


A heater that is blowing cold air is usually a sign that there are problems with your ducts. Keep in mind that the warm air from your system travels through the ductwork. Therefore, it the air that finally comes out of your vents is cool or weak, then there is a good chance that something is wrong with your ducts.

Outdoor Temperature

Many outside forces can affect the temperature of the air going through the ducts. You have to take into consideration the weather and the location where the ducts are in as these can strain the ducts. Add proper insulation to help keep stress and damage away.

Broken Ducts

Any ductwork that is full of tears and holes causes warm air to leak out of these damaged areas. It can also cause cool air to mix in with the warm air. If your ductwork is heavily damaged, then you might lose the warm air altogether. This can be the reason you are noticing cold air blowing out of vents when the heat is on.

Ducts are an essential part of your heating system. Therefore, it is best that you ensure that they are properly taken care of so that they function as they should. A professional can help you solve any ductwork problems you might have.


There are many other causes that cold air can come out of your vents. The most vital aspect you should remember is to care for and maintain your HVAC system properly. Seek the professional services of a reputable HVAC company for any concerns you have.