Why is My Furnace Blowing Cold Air? We Answer Your FAQs

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Why is My Furnace Blowing Cold Air?

Texas winters are rarely the stuff of legend but that doesn’t mean that you shouldn’t be comfortable in your own home. Feeling a cold draft from your vent could point to a number of easy to solve problems that prevent future discomfort or an unnecessary call to an emergency HVAC specialist.


The Dial One Johnson team—the HVAC repair Grand Prairie, TX, knows and trusts—has put together some of the most common reasons and DIY fixes for a furnace that is blowing cold as well as what to do in the event of an HVAC emergency. Should you need further assistance, our team of licensed HVAC contractors are here to help with all HVAC repair needs.

Common Causes (and Cures) for a Furnace Blowing Cold Air

Here are some of the most obvious signs that something is wrong with your furnace… and expert guidance on what to do about it.

Check the Thermostat

Your thermostat should be the first thing that you inspect when you notice that your furnace is pushing out cooler air than is expected. Perhaps you bumped it or another family member has adjusted the settings. It is easy to go about your day and forget to readjust, especially when it’s warmer and you don’t really need the heat. Here are the questions to ask as you assess whether your thermostat is functioning properly:

1. Is the Thermostat Set to Cool?

For homeowners outside of Texas, this one might seem a bit ridiculous. For those in North Texas, too common are the days that we experience all four seasons in less than 24 hours.


It is easy to leave the setting on cool after a warm day. Or, perhaps you have a cold natured person in your home that flipped the setting without you knowing (thermostat wars, anyone?). It can be easy to bump the wrong button or switch, inadvertently turning it on “cool.”

2. Is the Thermostat Set to Fan Instead of Auto?

You have checked that the thermostat is set to heat but still notice that cool air is blowing. Make sure that the system is set to auto, instead of fan.


Auto will only force air based on your heat or cool setting, whereas the fan setting will blow constantly regardless of the setting. Most homeowners leave their system on the auto setting as it can help reduce energy costs.

3. Did the Batteries in Your Thermostat Die?

For most homeowners, there is a good chance that you don’t look at your thermostat daily. Newer thermostats—that are battery powered—will not operate correctly when the battery dies.


Smart thermostats send alerts to your phone when the battery needs replacement. Regardless of your thermostat’s age, it is always a good idea to keep replacement batteries on hand. This alleviates a last-minute run to the store and prevailing discomfort while you wait.

4. Have You Recently Replaced Your Thermostat?

With new home technology coming out all the time, it is exciting to update your home’s thermostat and experience all of the interconnectivity that is possible. 


But did you know that not all thermostats are compatible with all HVAC systems? If your system is set to heat and auto but is still not working properly, there is a good chance your new thermostat is to blame.


If you installed the thermostat yourself, consult with the instruction manual to ensure that the wiring was done properly. Should you run into any issues, Dial One HVAC repair in Grand Prairie, TX will be happy to assist.


If the unit was installed by a professional, contact the company and report the problem. They should send a technician out at no cost to remedy the situation. 

5. Has the Thermostat Gone Bad?

Like other parts of the HVAC system, the thermostat is not designed to last forever. Usually you can expect that it will last as long as the main unit, somewhere around 15-20 years.


Before rushing out to buy a new thermostat, adjust the heat to the maximum setting and turn it back on. If nothing happens, you know that you need to replace the thermostat.


Even the most experienced homeowner can overlook their thermostat from time to time, but always remember that it is a great checkpoint any time your furnace is not heating properly.

Check the System

HVAC systems are complex and any repairs should be done by a licensed professional. That said, understanding what your furnace needs to produce heat will help with further diagnoses.


Three things are needed for a furnace to produce heat: fuel, a spark and oxygen. When one or more of these are not working, the system will not be able to produce heat and could be the reason behind a drafty home.

1. Fuel

Gas furnaces are powered by natural gas. In the event that gas is shut off or disconnected, the system will not produce heat.


Common to systems that were shut down for the summer or longer periods of time, you may need to turn the gas shut-off valve back into the ON position. This also goes for systems that have recently been serviced by a technician. They may have simply forgotten to open the gas valve back up.


Additionally, most energy providers notify customers of any outages or work that is being done in their area that could impact service. 


Homeowners who have electric furnaces can expect the same issue in the event of power loss. First, check your breaker to make sure that nothing is flipped. Newer systems will have a conveniently located RESET switch on the front of the inside unit. Test this to see if it resolves the issue.

2. Spark

You have fuel coming into your system, but there is still no heat. A lack of ignition or spark could be to blame. After all, natural gas passing through your HVAC system does nothing if there is nothing to ignite the fuel.


Older homes may still have furnaces that are ignited by a pilot light, however it is worth noting these types of systems are not installed in newer homes. If your furnace is older, it could be time to upgrade your system to one that is safer and more efficient.


For electric units, the RESET button is the best place to start. Reset the unit then wait for the HVAC system to start, listening closely for the clicking noise that the ignition switch will make. If you don’t hear anything, call your local HVAC contractor to schedule an inspection so that they can help with repairs or replacement as needed.

3. Airflow

The final component needed to create heat is oxygen, or airflow. A clogged air filter is a common cause if your furnace is not producing heat.


Inspect the air filter and replace if needed. A good habit is to have an extra air filter in storage in the event clogging occurs faster than expected. Checking your air filter monthly is part of properly maintaining your HVAC system, with replacement needed every 3-6 months or as needed.

Find HVAC Repair – Grand Prairie, TX

With proper maintenance the chances of an HVAC emergency are greatly reduced. Despite a homeowner’s best efforts, emergencies will come up from time to time. In the event of a furnace malfunction, the #1 thing to remember is safety.


While sub-zero temperatures are quite rare in Grand Prairie, TX, anytime the temperature drops you will want a furnace that works.


The Dial One Johnson team is the trusted source of HVAC maintenance and repair by homeowners across Grand Prairie, TX and the entire Dallas-Ft. Worth Metroplex. With offices in Midlothian and Cedar Hill, offering 24-hour emergency assistance, you can count on our team of licensed, professional HVAC experts to get the job done quickly. Contact us to schedule an appointment today.


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