Before the outside temperature gets colder, you want to test your furnace to ensure it is operating correctly. The last thing you want on a cold day is a heater that does not work. There are some common reasons why your furnace may be blowing cold air. Some may have simple solutions, while others require professional help. If your furnace exhibits one of the below symptoms, contact Comfort Systems today so a technician can assess your heating system.

Thermostat Settings

The temperature setting on your thermostat is what allows you to stay comfortable. As the seasons change, you may need to adjust your settings. When you first notice cold air coming from your furnace, you should check your thermostat settings. You may need to change your settings from air to heat. Some smart thermostats may be able to do this automatically, but others require manual adjustment. You also want to ensure your thermostat is set to auto and not on. When your system is set to auto, this provides the most efficient functioning. When set to auto, the fan and furnace come on at the same time. If it is set to the on position, the fan is on all the time and can blow out cold air.

Air Filter

When the air filter is clean, it allows clean and fresh air for your house. When it is dirty, it blocks the air around the heat exchanger on your furnace. This can cause your system to blow cold air. It may also cause the system to overheat. When your furnace overheats, it trips the high limit switch to shut down the system. This prevents fire and extensive damage to your unit. You can assess the condition of your filter by inspecting it. If it is dirty, replace it. It would be best if you replaced your filters regularly throughout the year.

Pilot Light

Depending on the age of your heater, it may have a pilot light. Newer heaters do not have them. However, if yours is an old heater, it has a pilot light, and it is out, you will not get hot air in your home. The pilot light is a blue flame that heats up the system. When the light is out, it will not heat the air in the furnace. You can use a lighter to relight the flame. You can do this yourself but can contact a professional to do it for you.

Overheated Furnace

If only cold air is coming from your furnace, it could be because the system overheated. Your heater has a safety feature that turns it off to prevent fire, leaking carbon monoxide, or a possible explosion. There are various reasons why your system might shut down:


If you have an older system, it may not function efficiently or perform as well as it once did. This can lead to your system reheating. Parts can wear out and require replacement, but with proper maintenance, your system can last as long as 15 years.

Buildup of Dirt

When your filter is clogged, it can blow cold air. If you replace the air filter, there can still be dirt left behind in the heating unit. This may cause your system to overheat. You may need a professional to clean your system.

Mechanical Failure

There are many parts in your furnace that can fail at any time. The older your heater is, the more likely this will occur. When there is a malfunction in your heater and parts begin to fail, this is likely to cause overheating.

Not Enough Warm Up Time

When you first turn on your heater, it needs time to heat the air coming out. If you notice your heater is blowing out cold air as soon as you turn it on, give it more time. It could take as long as 15 minutes to heat the air thoroughly. If, after 15 minutes, the air is still cold, there is another problem.

Air Duct Leak

There are air ducts in your heating system, and those ducts go throughout your home. If you notice cold air coming from your heating system, it could be that air is escaping through the ducts. Sometimes these ducts get holes in them which is the perfect place for air to escape. You need to contact the professionals at Comfort Systems to check your ducts and seal up any holes.