Why Your Furnace Blows Cold Air and How to Fix It

When it’s cold outside, there’s nothing like the instant relief of walking into your toasty house, and feeling the heat of your furnace warm you from your head to your toes. Alternatively, few things are more disappointing than cranking up the thermostat, but to your utter dismay find that your furnace blows cold air, giving you no relief from the cold weather.

Newcomers to Las Vegas don’t always realize that it can get cold in the desert. While Las Vegas doesn’t have as many cold months as other places, residents know it still gets very cold during our winters. A furnace blowing cold air is a major inconvenience, making your home uncomfortable and can even contribute to higher energy bills.

So, what exactly causes your furnace to blow cold air, and what can you do about it? The reasons (and their fixes) may be simple; other times they can be more complex and require professional help to ensure safe and efficient repairs. Attempting DIY fixes on complex issues can lead to safety hazards such as gas leaks or electrical malfunctions. Always refer to the safety warnings on your equipment and their user manuals.

Below we’ll discuss “why my furnace is blowing cold air”, and will offer both DIY and “call for help” solutions for furnace repair in Las Vegas.

Why is my furnace blowing cold air?

The Thermostat is Set to On Instead of Auto / Other Thermostat Problems

The first thing to check is the fan setting of your thermostat. One of the reasons your furnace may be blowing cold air is that this is set to “On” instead of “Auto”. If this is the case, the fan will run all day, even when the furnace isn’t heating. By turning it to “Auto”, the fan will only blow when the furnace is actively heating. If this is the issue, simply re-set your thermostat to “Auto”, and your furnace should stop blowing cold air.

If you have a programmable thermostat, check that your schedule is set to the correct temperature for each time of day. Change the thermostat’s batteries if they seem to be running low. 

The Heater Hasn’t Warmed Up Yet

If you hear your furnace kick on but there is no airflow, or there is cold airflow, it may just be that the heater hasn’t completely warmed up yet. Many furnace models heat the air before the blower fan begins to move it into your living areas.

Check your furnace’s user manual (or look it up online) to see if there should be a blower delay after the heating component kicks on. If, after a few minutes, the furnace is still blowing cold air, it may be time to have our technician provide a deeper diagnostic for heating repair.   

The Pilot Light is Out (Gas Furnaces)

Pilot lights used to be a standard component on gas furnaces. Though the emergence of pilotless systems has become more common, there are still many homes with piloted furnaces. If you’re feeling cold air coming from your furnace, it may be because the pilot light has not ignited the primary heating unit.

Start by checking that your thermostat is set properly. Next, go to your furnace and locate the pilot light assembly to see if there is a flame. If the pilot is out, follow the manufacturer’s directions to relight it. If the pilot won’t stay lit, it may be time to call a professional.

Dirt on the Flame Detector (Non-Piloted Furnaces)

Gas furnaces that do not rely on a pilot light instead use what’s called a flame detector. Its job is to detect when the flames turn on and off to ensure a proper heating cycle. If your flame detector gets covered in dust, dirt, or grime, the furnace will essentially “be confused”, and start blowing cold air. You can clean the flame sensor in your furnace, or have one of our professionals help you with heating repair.

Your Furnace Overheated Due to Dirty Filters and/or Closed Vents

Filters play a critical role in preventing harmful dust and debris from reaching the sensitive interior of your furnace. But as filters become clogged with dirt, the air can’t reach your furnace either, causing it to work harder and overheat. The furnace’s safety sensors then shut it down to prevent further damage.

The same problem can occur if too many vents are closed at once. Some homeowners close the heat vents in rooms that go unused in the winter. A couple may be fine, but avoid closing lots of vents.

If you notice airflow from your vents seems weaker and cooler than it should be, or if you hear the furnace running for short periods before shutting down (we call this “short cycling”), then dirty air filters or closed vents may be to blame. Change your filters every 2-3 months, and keep enough vents open. If problems still persist, we recommend setting up a furnace repair appointment. 

The Fan Limit Switch Has Malfunctioned

If your furnace is not blowing hot air, or is not operating at all, this part may have malfunctioned. Your thermostat may also show an error message. The fan limit switch (also called high limit switch) measures the temperature inside the furnace and shuts it down if it ever gets too hot. But if it malfunctions, the fan may still blow air even though it’s not hot.

Start by checking the filters. As mentioned earlier, blocked airflow can cause your furnace to overheat, which will trigger the limit switch. If cleaning or changing the filters does not work, an HVAC professional will likely have to repair the limit switch.

There’s Damage to Your Ductwork

If you notice your heater blowing cold air or an increase in your utility bills, you should check your ductwork. Even with your furnace heating properly, punctures or broken connections in the ducts can leak hot air escaping, and cool air from the attic entering the ducts. Or if the insulation has peeled away from a duct, heat can escape through the unprotected surface. Such issues grow more common in old ductwork.

If you’re inclined to fix things, you can probably fix simple leaks by straightening sheet metal, tightening connection screws, or using tape

 or sealant appropriately rated for ductwork. If you continue to have problems, it is time to call a professional for duct sealing. 

The Condensate Line is Clogged

If you’ve noticed your furnace not working, a clogged condensate line is a potential problem. These drains help remove moisture from the air. But if a line gets blocked by buildup or other debris, this may deactivate the burners, causing your furnace to blow cold air. A professional heating repair technician will be able to check for condensate blockages.

There’s a Problem with the Gas or Oil Supply

A fuel supply issue can make your furnace blow cold air, turn on and off repeatedly, struggle to keep its pilot light on, or not operate at all. If you suspect a fuel supply issue with your furnace, it’s probably best to call a professional to repair your furnace.

There’s a Problem with the Computerized Controls

Is your furnace running but not blowing hot air? Maybe your room temperature fluctuates seemingly without reason? Or can you hear your furnace’s operating sequence seem out of order (for example, starting the blower fan before the heating flames ignite)? These signs can indicate a problem with the system’s central control board.

The control board is the brains of your HVAC system. These usually have many wires, lights, indicators, and inputs. If you have a control board going out, we highly recommend calling a professional technician for assistance with your furnace repair in Las Vegas.

Tips for Preventing Furnace Problems

• Regular Maintenance: Schedule annual furnace maintenance to ensure your system is operating efficiently and safely. A professional furnace repair technician can inspect your equipment, clean components, and identify potential problems before they become major issues.
• Replace Your Air Filters Every 1-3 Months: Using high-efficiency air filters and replacing them before getting clogged up is crucial to not just your furnace health, but just about everything inside your HVAC system. Forgetting to change your filters can significantly decrease the lifespan of your air conditioner and furnace.
• Energy-Efficient Upgrades: Consider upgrading your furnace to a more energy-efficient model. Modern furnaces are designed to be more efficient and can help you save money on your energy bills.

Reliable Furnace Repair &Installation in Las Vegas

If your home’s furnace is blowing cold air even though it’s set to heat, we at Sunrise Service have got your back. Our experienced HVAC technicians will diagnose and repair or install your furnace quickly and efficiently, making sure that every wintry day you flick on the heat, you get heat!

Call Sunrise Service today at (702) 568-5300 or fill out our easy service request form to get quick, effective furnace repair in Las Vegas at prices you’ll love.

We also provide comprehensive HVAC services such as air conditioning repair, including 24/7 emergency HVAC repairs. We’re proud to have served all of Las Vegas, Henderson, and Boulder City for over 30 years.

Photos by Sunrise Service; Slaapwijsheid.nl on Unsplash

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