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Why Is My Heater Blowing Cold Air: Top 8 Reasons

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Have you turned on your heat only to realize the furnace is blowing cold air? There are multiple reasons this could be happening. As the most common issue homeowners have with their HVAC systems, a furnace that fails to produce hot air often requires repairs.

Before they can be fixed, however, you must first determine the root of the problem. When you ask yourself, “Why is my heater blowing cold air?” our team has the answers for you.

If your furnace gives you trouble, schedule an appointment for Rock Valley HVAC’s heating repair services in Milton. Our team can assess your unit and make any necessary repairs. Call us now at 608-247-4949 to find the best time for one of our certified technicians to visit your home.

Until then, let’s look at the top reasons your heater is blowing cold air.

1. It Hasn’t Warmed Up

If you just turned your heat on for the season or increased the temperature settings, your furnace will need time to adjust. Give it 10 to 15 minutes for the air to warm up. After that, if the air is still cold, something else likely causes the issue.

2. Wrong Fan Settings

Most furnace fans have three settings: On, Off, and Auto. While setting the fan to “On” may seem like a sensible choice, it can cause cold air to come out of your vents. This is because the thermostat’s “On” setting keeps your furnace fan running constantly.

While that works well while the furnace operates, the fan will still run when the heat turns off or the system has completed its heating cycle, resulting in cold air. Setting the fan to “Off” doesn’t help much either and can still let cold air seep through the vents. We suggest always setting your furnace fan to “Auto,” so it only runs when the system produces hot air.

3. Thermostat Batteries Are Low

Sometimes when thermostat batteries get low, they reset your temperature preferences. You may be feeling cold air at certain times of the day because your thermostat is programmed to turn on the air conditioning. Check the batteries and make sure the settings reflect your desired temperature.

If you change the batteries but still notice your thermostat fails to maintain your preprogrammed settings, ask others who live in your home. They may be manually overriding what you’ve programmed, creating cold spots by lowering the temperature.

4. Pilot Light Is Out

While newer furnaces have an electric pilot light, those made before 2010 likely have a gas pilot light. If the pilot light is out, your furnace will only blow cold air. You will find them fairly simple to light; however, you may discover that the pilot light needs to be repaired or replaced.

To determine if it needs to be repaired, light the gas pilot light and see if it remains lit. If it doesn’t, you should contact a professional to take a look as it probably needs to be replaced.

5. A Clogged Filter

Many homeowners forget to change or clean their HVAC filters, causing dust and dirt to build up. Not only does this impact your energy bills and indoor air quality, but it can also cause blockages. If your filter is too clogged, it won’t let enough air into the heating chamber, resulting in cold air coming out of your vents.

Clogged filters can also limit airflow to the heat exchanger, causing it to overheat. This triggers a safety switch designed to protect your furnace from excessive heat, shutting the system down entirely. When this happens, you’ll be stuck with cold air blowing out of your vents.

Fortunately, a clogged filter entails an easy fix. If your HVAC system uses disposable filters, you can buy new ones for a few dollars at your local hardware store. Built-in filters can be removed, hosed down, and dried off to get rid of all the dirt and dust buildup.

6. A Faulty Flame Sensor

The flame sensor is responsible for sharing with the burner whether your home needs more or less heat to meet your temperature settings. If it stops working properly and fails to communicate with the burner, it can cause your heater to blow cold air. Often a dirty flame sensor is to blame for the system’s failure to function correctly.

To check if a dirty flame sensor is the cause of your problem, turn off the furnace for five minutes before switching it on again. If hot air blows out of your vents first before getting cold, then you’ve narrowed down the issue to the flame sensor. Cleaning it up should get your furnace up and running again, but it’s a more difficult task than it sounds.

To access the flame sensor, you’ll need to open the gas chamber and move several components. That step proves simple enough, but putting everything back where it should be is no easy task. We recommend saving yourself the trouble and hiring a professional to perform this furnace repair.

7. A Blocked Condensation Line

A high-efficiency gas furnace forms condensation when working properly and requires a special plastic vent pipe (PVP) to continuously drain the water. Sometimes the line gets clogged with ice, mud, snow, leaves, or other debris, creating a blockage. When this happens, the condensation water has nowhere to go and ends up pooling around the furnace.

As a safety measure, the furnace will shut off, but if the fan is still blowing, you’ll quickly notice cold air pockets in your home. To fix the problem, locate the HVAC system’s PVP pipe and see if the clog is easy to address. Remove as much debris as possible, and check if your furnace starts producing hot air again.

If the PVP pipe is clogged with ice or broken, you will need to call in a professional to handle the job. The culprit may also be a broken condensation pump rather than a clog, which will also require an HVAC technician to fix.

8. Out of Fuel

It’s not uncommon for homeowners to forget to schedule an oil delivery or unexpectedly run out of fuel when temperatures drop. You may not realize what the issue is right away, though, as all the electrical functions for the furnace will work as usual. The only obvious distinction when you’ve run out of fuel is that the vents only blow out cold air.

If you fail to pay your gas bill, you will experience similar results. Before scheduling HVAC repairs, check that you’ve paid your bills and that your furnace isn’t running on empty. Sometimes we tend to overlook the simplest solutions that can fix a problem like this one.

Still can’t figure out why is my heater blowing cold air? It’s time to get the professionals involved.

Schedule an HVAC Appointment in Milton, WI

Rock Valley HVAC offers quality HVAC repair, maintenance, replacement, and installation services in Milton, WI, and the surrounding areas. Our team of certified technicians is highly trained and experienced in the industry, making us one of the most trusted HVAC businesses serving our community. Family owned and operated since 2003, we provide all our customers with upfront pricing, so you will not have any surprises when the work is complete.

When you work with Rock Valley HVAC, your satisfaction is guaranteed! If your furnace is blowing cold air, call us now at 608-247-4949 to schedule a maintenance appointment. Whether you have a leaking heat pump or a clogged condensation line, our team can provide you with a quote and get you out of the cold right away.