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Why is My Furnace Blowing Cold Air?

Written by Vaughan Comfort Services on . Posted in , .

While the weather in southern New Jersey is mild compared to some places in Canada or the Midwest, average highs in January still only reach around 40°F, and around 47°F by the end of February. With studies revealing that people feel more comfortable around 70°F, it’s no wonder that warm air from HVAC systems is so vital to keeping homeowners functioning at their best. The last thing anyone wants in the winter is cool air blasting from their furnace.

If your furnace is not functioning properly, count on Vaughan Comfort Services’ team of HVAC professionals to help you troubleshoot and resolve any issues. You can schedule your appointment online or call us at 856-627-0303 today.

Is Your Furnace Blowing Cold Air? Here Are 11 Common Reasons Why

There are many reasons why your furnace might blow cool air instead of hot air. Some of the most common causes of a malfunctioning furnace range from thermostat issues to problems with electrical or electronic systems to dangerous gas leaks and beyond. When the issue is less than straightforward, count on Vaughan Comfort Services to troubleshoot for you.

1. You Have Issues With Your Thermostat

It is easy to set programmable thermostats incorrectly until you get the hang of using them. If your thermostat’s fan setting is on, it may blow air without activating the furnace. The first step is checking your heating system to ensure that the thermostat setting is on heat rather than cool or fan. If the thermostat is set properly and you are still not getting heated air, you may have another issue.

2. Your Circuit Board is Malfunctioning

If the blower motor and thermostat are the heart and soul of the HVAC system, the circuit control board is the brain. Your circuit control board tells the furnace what to do and when, coordinating the communication between various components. The circuit board relays commands from the thermostat to the burner and blower motor. If it malfunctions, the entire system goes down, or it can randomly turn on the blower without igniting the burners.

3. Your Furnace is Overheating

Almost every new gas furnace has safety systems in place to prevent the disasters that can occur when dealing with natural gas. One of these safety systems is a limit switch whose purpose is to detect when the furnace is in danger of overheating and shut it down. Sometimes, this can lead to the blower fan continuing to run, which will move air through the house, but it will be cool air instead of hot.

4. The Furnace is in Safety Mode

Safety mode is a function of your HVAC system that stops heat from accelerating to dangerous levels. Safety mode turns off the ignition in your furnace so the burners do not light. Your furnace could be going into safety mode for several reasons, including the following:

  • Your furnace is overheating.
  • Your limit switch is faulty.
  • There is a crack in your heat exchanger.
  • You have a corroded or bad thermocouple or flame sensor.
  • A malfunction triggers safety mode incorrectly, which often happens with older furnaces.

Your HVAC technician should be able to diagnose the problem if you are experiencing any of the following issues.

5. The Pilot Light Is Out

Older furnaces use a pilot light as a standard feature. A pilot light is a small flame that is always lit. It lights the burners when the circuit board opens the valves to blow gas through them. The pilot light can go out for a variety of reasons. Often resetting the pilot light can be done by the homeowner.

To reset the pilot light, try the following steps:

  1. Locate the pilot assembly and its reset toggle, usually near the bottom of the furnace.
  2. Turn off the toggle and wait a few minutes to allow any excess gas to dissipate.
  3. Switch the toggle to the on position, hold the reset button, and place a match in front of the pilot. You should see a flame light.
  4. Release the reset button.

If you smell excessive gas or cannot get the pilot light to re-light on its own, you should call an HVAC expert for troubleshooting. Do not risk a disaster with a natural gas leak.

6. You Are Out of Fuel

Some furnaces do not use natural gas for fuel. They may use heating oil, propane, or other combustible materials. If you run out of fuel in your furnace, it may continue to run, but without fuel for the furnace burners, it will just blow cold air. You will need to contact your fuel provider to refill your HVAC system.

Even if you have a natural gas furnace, your gas supply line may be shut off on the outside or inside. Check your gas valve near the furnace to be sure that gas is properly flowing. Call your natural gas provider or a furnace repair professional for help if the valve is open and you still have no gas.

7. You Need to Replace Your Air Filter

You should change your air filter several times a year. Most HVAC technicians recommend four times per year at the changing of the seasons. A dirty air filter can restrict airflow and trap heat in the furnace, resulting in cold air. A clogged filter is very bad for your furnace, so you should avoid this easy-to-fix issue.

Changing your furnace filter is an easy DIY furnace repair and maintenance piece. Simply locate the filter on the front or side of your furnace, remove the access plate that holds it in place, pull out the old, clogged filter, and replace it with a fresh, clean one.

8. Your Vents or Evaporator Coil Are Clogged

A clog in your vents or evaporator coil can present a risk to your furnace. Not only will you get cool air blowing instead of heated air, but it can cause damage to the entire system. You may be able to clear some blockage from vents yourself.

Evaporator coils are only present in HVAC systems that include air conditioning. Even though they are part of the AC system, the air still has to pass through them. A clog will make it difficult for air to pass through, which can result in the air from your vents being cool.

9. Your Ductwork Needs Repairs

Your ductwork is how air travels through your home from the HVAC system. As it ages, a buildup of dirt; particles or dust; or, in the worst situations, mold; and other dangerous substances can clog up the ductwork. Old ductwork can also break, crack, and get holes in it.

If any of these issues exist, your furnace may blow cold air as the heated air gets backed up and cools down before it reaches the vents. A furnace repair professional can analyze issues with your air ducts and get them working properly again.

10. Your Flame Sensors Are Dirty

Furnaces have different types of flame sensors. They are especially common in furnaces that do not use a pilot light. These flame sensors detect when the burners are lit. They stop working when covered in carbon deposits, dirt, dust, and other buildup and grime. To get your flame sensors working again, call an HVAC maintenance professional to clean them.

11. Your Drain Lines May Be Clogged

If you see excessive condensation around your condensate drain lines (indicated by water pooling around the base of the furnace), seek help from an HVAC service company. This means that your condensate drain lines may be clogged, which can back into your system and damage the furnace. Sometimes it can create issues with mold that can spread throughout your home and present health risks to your whole family.

Knowledgeable homeowners may be able to clear out some of this buildup. However, calling the pros is the right thing to do if it is your first time dealing with this issue.

How Do You Fix a Furnace That Blows Cold Air?

man adjusting a thermostat

Troubleshooting your furnace for simple fixes is the first step you should take. Often, furnace problems result from something quite simple that can be a DIY fix.

Check Your Thermostat

The first step is to check your thermostat to ensure it is running your heating cycle properly. Check that it is programmed to run at your desired time and temperature, and on the heat setting rather than cool or fan. Also, check to see if it is showing an error code or is blank. If it is, consult your manual to see what the error means and explore whether you can fix it yourself.

Examine Your Vents and Ductwork for Blockages

Check the entries to your vents and ductwork to look for blockages or clogs that you can see and clear yourself. In some cases, the blockages may be too far inside the walls, and you may need help from a furnace maintenance professional.

Replace Dirty Filters

Replacing dirty furnace filters is easy: You just remove the old ones and slide in the new ones. If you do it four times a year, at the changing of seasons, it will be easy to remember and can become a normal part of your annual home maintenance.

Call the Service Experts at Vaughan Comfort Services

Getting regular service maintenance from expert HVAC maintenance technicians can not only prevent your furnace from having problems, but it can also save you money by catching issues before they become too big. An HVAC technician should service your furnace at least twice a year, if not more often. The experts at Vaughan Comfort Services are ready to keep you reliably warm all winter.

When Should I Replace My Furnace?

There is no easy answer to this question. Most experts estimate that typical furnaces last between 10 and 15 years. Sometimes, well-maintained furnaces can last longer. It will depend on your furnace, the size of your house, how hard the device works, and various other factors. Your HVAC technician can let you know when to consider a new furnace installation and provide you with options.

Looking to Stay Warm This Winter? Call Our Service Experts

Our South Jersey expert technicians can troubleshoot your furnace issues and let you know if a new furnace can save you in the long run. Call us today at 856-627-0303 or schedule a service visit online.

NJ LIC. NO.13VH01727600
Robert W. Vaughan,
Master HVACR Contractor Lic. # 5842
Thomas J. Weaver,
Master Plumber Lic # 9521

Contact Info
212 Barrett Avenue
Magnolia, NJ 08049

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