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Why Is My Furnace Blowing Cold Air?

April 26, 2023

A furnace should keep your home warm and cozy during cold weather, especially during the intense winters we experience here in Utah. But sometimes furnaces have trouble keeping up, which could result in a furnace blowing cold air.

“Why is my furnace blowing cold air?” is a question we often get at YES! Many factors can cause your heating system services to blow cold air, such as dirty furnace parts, damaged ductwork, clogged air filters, and problems with components. Some of these issues are easy to fix yourself, but others require professional heater repairs. Learn why this is happening and when to call the professionals at YES!

Table of Contents

14 Reasons Why Your Furnace is Blowing Cold Air

Fixing and Preventing Heating Issues

The Importance of Furnace Maintenance

14 Reasons Why Your Furnace Is Blowing Cold Air

Various reasons can cause a furnace to blow cold air, ranging from something as simple as needing a quick clean to something complex like a component repair or replacement.

1. Little to No Gas Is Supplied

This problem may seem obvious, but your furnace could be blowing cold air because of a problem with the gas supply. The supply may have run out, or the gas supply line may be experiencing an issue.

If there is a problem with your gas line, it’s not a problem you can solve alone—call YES! at 844-216-9300.

2. Air Filter Is Dirty

Your furnace contains a disposable mesh screen called an air filter. The filter plays an important role in keeping your furnace clean and the air in your home safe to breathe. Over time, the filter will get clogged, resulting in a reduction in its effectiveness.

To fix this issue, simply replace the old filter with a new one in the correct size. Our technicians recommend replacing the filter at least every three months for the best results. Replace it more frequently if you have pets or live in a pollen-heavy area.

3. Thermostat Batteries Are Dead

Many thermostats are battery-powered. When the thermostat batteries run out of juice, the whole device will stop functioning properly, and your furnace won’t kick on.

If the thermostat is the source of your furnace blowing cold air, a fresh set of batteries will do the trick.

4. Incorrect Thermostat Settings

There are a couple of thermostat issues besides the batteries to remember. For example, what is the temperature setting on the unit? If you have multiple people in your household, someone may have changed to a lower temperature, so your heater won’t produce hot air.

5. The Fan Is Set to On

If the fan is on, it will run continuously—meaning your furnace blows cold air between heating cycles. Try switching the fan back to auto to see if hot air is restored. It also doesn’t hurt to double-check and ensure your thermostat isn’t set to air conditioning instead of heating—just about everyone has made that mistake once or twice, particularly during the unpredictable seasons when using both settings on the same day.

6. Pilot Light Is Out

The pilot light going out applies to homes with gas-powered furnaces. Most residential furnaces are powered by gas, but some modern units are entirely electric.

Gas furnaces have a component called a pilot light, which ignites natural gas and turns it into heat. If the pilot light burns out, your furnace won’t be able to generate heat, and the temperature in your home will plummet.

Since changing the pilot light involves opening the furnace, we recommend not trying this at home. Let our trained technicians at YES! take care of safely replacing the pilot light.

7. The Control Panel Is Glitching

Many newer furnaces have electronic control panels to help regulate the temperature more accurately than older models. The control panel occasionally acts up but can be reset via the main power switch.

Depending on your furnace model, the switch will be on the unit or a nearby wall. You can check your furnace manual to find the exact location.

Once you locate it, turn the switch off, wait a few minutes, and then turn it back on. The electronic controls should reset and enable your furnace to start making hot air again.

8. Valve Is Clogged

If the pilot light won’t kick on, you may have a stuck valve. Valves can get stuck due to dirt or debris. This problem is especially common for furnaces that aren’t cleaned often or don’t undergo regular maintenance tune-ups.

A seriously dirty furnace can cause the entire system to overheat and shut down. This issue results in cold or room-temperature air.

You can have your furnace cleaned and checked by a technician from YES! If the valve is clogged, we’ll remove the debris and clean out the entire system so it doesn’t happen again. You can also schedule an annual maintenance appointment to keep your heating system clean for the long run.

9. Flame Detector Is Dirty

In addition to causing clogged valves, dirt, and debris can cause other concerns within the furnace. If your flame detector is dirty, it can prevent the unit from generating hot air. Flame detectors register a flame occurring while your gas furnace runs. If it doesn’t detect a flame, it turns off the gas.

If your detector is covered in dirt, it can’t detect a flame, causing the heating process to stop. To fix this issue, you only need to clean your flame detector. However, because a flame detector is essential to a furnace's functionality, it’s better to call professionals to clean it.

10. Condensate Lines Are Clogged

Mixing heated air with cold air can create condensation, which causes problems for your furnace. This concern is why heaters (and air conditioners) have condensate lines—they prevent condensation buildup.

If your condensate line is clogged, that excess liquid could affect the sensors used to heat the furnace. You’ll need a professional to unclog your condensate line and get your heater up and running.

11. Ductwork Is Damaged

Another reason your furnace blows cold air is damage in the ductwork running through your house. A problem in the ducts can be as small as a crack or as large as a visible hole—all of which cause hot air to leak out before getting to you.

Damaged ductwork requires locating the source of the problem and fixing it. You can run your hands along the ductwork you can access to determine if you can feel any air blowing up. If it’s a small crack, you can use a sealant, but if it’s more than that, it’s time to contact YES!

12. Fan Limit Switch Is Having Problems

A fan limit switch controls the airflow and measures the temperature within your furnace. If it’s not working correctly, it may continue to blow air even after your furnace stops heating—resulting in cold air coming through the vents. This problem could also completely shut down your furnace.

To fix this issue, you should look at the air filter. If it’s too dirty, it can restrict how much air moves through the system to the heat exchanger, which causes overheating, triggering the fan limit switch.

If replacing the filter doesn’t work, call YES! at 844-216-9300.

13. The Heater Needs to Warm Up

This is another obvious but easy-to-miss reason your furnace is blowing cold air: Your furnace just needs more time to warm up. Not all furnaces can produce hot air as soon as they kick on. If you’ve heard your heater turn on, but cold air is blowing, give it a few minutes to warm up.

If that’s not the solution, you may need to contact YES! to schedule an appointment to have a technician look at your furnace.

14. Too Many Vents Are Closed

Turning off vents in rooms that aren’t often used can affect how your furnace works. It may stop working after a few minutes or only blow cold air because it perceives that the space is warm enough. When it stops heating the space, the rooms you use start to feel chilly.

If you’re struggling with your furnace, make sure to check all your vents. If you have closed some, open them up and try the furnace again.

Fixing and Preventing Heating Issues

You can take steps to reduce the risk of heating issues that cause your furnace to blow cold air. Replacing the filter regularly, keeping the equipment clean, and staying current with maintenance are just a few ways to ensure efficient operation.

How Does a Furnace Work and What Is Happening Technically to Make It Stop Blowing Cold Air?

A furnace uses fuel to generate heat and a fan to push the heat into your space. The heat travels through ductwork to spread warm air throughout your home.

Generating heat involves many steps and relies on multiple parts within a furnace. Even one minor problem with a single component can cause the air blowing out of the unit to feel cold rather than warm.

Is Cold Air Blowing a Common Sign of Needing Repair or Replacement?

A furnace blowing cold air can be a common sign of needing a furnace repair or replacement. Other common signs that your furnace is on its last legs include unpleasant odors, leaks, and odd sounds.

Why Is My Heater Working but Not Blowing Heat?

If your heater is operating but not blowing heat, it may have to do with the settings or fuel supply. Review the most common reasons for this concern:

1. Incorrect Temperature

Similar to a heater blowing cold air, an incorrect temperature setting on the thermostat could cause your heater to run but not emit heat. Your temperature setting may already align with the current level within the home, which will allow the furnace fan to run but not heat the air.

2. Requires Warmup Time

If you know your furnace is on and working but is still not blowing hot air, give it a few minutes to warm up to see if that makes a difference.

3. No Fuel

If your furnace has no access to fuel, it cannot create heat. Your pilot light will be on, but there’s nothing to burn, which leads to non-heated air blowing through the vents.

Make sure to check your fuel supply and lines. If there’s a problem with your line, technicians at YES! can help.

4. Dirty Filter

We’ve already mentioned that clean air filters are crucial to the operation of your heater. If your filter is too dirty, it will restrict airflow, and the unit won’t blow hot air. Some furnaces will turn off completely to prevent overheating.

The Importance of Furnace Maintenance

There aren't many things worse than having your furnace break down in the middle of a Utah winter—which is why you need to maintain the unit consistently. People tend to only think about their furnaces when they want to use them but can’t due to maintenance issues.

Keeping up with regular maintenance checks can prevent the problems above from happening. Additionally, your technician can look for signs of trouble and resolve them before it gets too cold outside.

Benefits of Furnace Maintenance

Keeps It Clean

Getting your furnace checked out by professionals like the technicians at YES! will help you know if your furnace needs a thorough cleaning. As shown above, a dirty furnace can cause a variety of problems. Knowing your furnace needs cleaning before a problem presents itself gives you ample time to schedule an appointment with YES!

Ensures Clean Air Filters

A fresh air filter can resolve some of the problems outlined above. During your maintenance service, the technician will assess the filter and can replace it if needed. Changing the filter regularly will prevent clogging, allowing your furnace to work better and have clean air in your home.

Boosts Efficiency

Regular maintenance checks ensure that your furnace is running efficiently. A technician can determine when parts are wearing down faster than others and suggest repairs or replacements before things get out of hand.

Ensures Safety

While furnaces are generally safe, they can become dangerous if they fall into disrepair. Maintenance checks ensure that everything is running properly and that any potential dangers, like gas leaks, are spotted immediately.

Addresses Minor Problems

As shown by the list of reasons why your furnace is blowing cold air, many of these problems started small and grew into more significant issues. A skilled technician can spot minor problems like cracks in your ductwork or clogs beginning to form in your lines before they stop your furnace from operating and cause more significant damage.

When professionals catch these issues early, the fix is often quicker and less costly than an extensive repair or a total replacement of your heating system.

Utah’s Heating and Cooling Experts

The winters in Utah can be quite chilly, so you naturally want to rely on your furnace to keep your home warm. If your furnace has stopped making warm air, there are a few ways to troubleshoot it for common issues.

If you’re still uncertain after running through this list, you can count on the technicians from YES! to figure it out for you. We’ll diagnose the problem right away and make long-lasting repairs.

You can also rely on us for all your heating and cooling needs, including maintenance, replacements, and installations. Call YES! at 844-216-9300 to learn more!

 

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Last Updated: April 15, 2025