Furnace Frustrations: 6 Possible Reasons Your Furnace Is Blowing Out Cold Air

Published September 17, 2024 by Tony Spezza

 

After letting your furnace hibernate for the spring and summer, you wake it up for the upcoming chilly season. 

Anticipating that oh-so-familiar musty smell and a gust of heated air, you turn on your furnace — but the warm air never comes. You’re only left with a dusty odor and a room-temperature stream of air jetting out of the vent. 

Or maybe you’re in the throes of December when your furnace decides to play it cool and worsen your winter woes by ceasing to work. 

No matter your situation, you’ve got a problem — your furnace is acting up, and you need a quick solution. 

In this article, we’ll answer your query, “Why is my furnace blowing cold air?” and offer a few troubleshooting tips and tricks for when your furnace is giving you the cold shoulder. 

Table of Contents

• Why Is My Furnace Blowing Out Cold Air?
• AAA Heating and Cooling: Portland’s #1 Solution for All Your Furnace Frustrations

Why Is My Furnace Blowing Out Cold Air?

So, you’re having furnace issues when you need it to work the most. You aren’t the first. 

At AAA Heating and Cooling, we receive a lot of service calls when it comes time for Portlanders to turn on their furnaces for the season. This is because your furnace is sitting dormant for the warmer months. It may have worked fine when you last used it, but if you’re not on top of your seasonal HVAC maintenance, you may have some troubles when it comes time to turn your furnace back on. 

We’ve been helping clients with these problems for years and have become familiar with every possible cause for why your furnace is blowing cold air. Let’s go over some potential scenarios and possible fixes. 

#1: Faulty Pilot Light

The first thing to check when your gas furnace is blowing cold air is the pilot light. Pilot lights ignite burners, which allow your residential HVAC system to build up and distribute heat. Older furnaces often have problems or damage to the pilot light from normal wear and tear, which can impede heat development. 

Aside from being out due to a strong draft or lack of use. Your pilot light may be out due to the following:

• Dirty flame sensor: Furnaces rely on flame sensors, otherwise known as flame detectors, to detect whether the pilot light is lit. If no flame is detected, the furnace will shut off to prevent harmful gasses from filling your house. A dirty flame sensor will prevent your furnace from registering your pilot light and heating your home. 

• Dirty or damaged thermocouple: A thermocouple is a sensor that measures temperature. Like flame sensors, thermocouples act as a failsafe that shuts off a furnace if the pilot light is out. Damaged thermocouples prevent gas from accumulating within a furnace. 

• Weak gas regulator: Pilot lights depend on a reliable gas source to remain lit. If there are issues with your gas valve or insufficient gas supply to the pilot light, it can go out. 

Solution

Try relighting the pilot light to see if that solves the problem. Our furnace installation professionals recommend the following steps:

1. Locate the pilot light assembly and its reset toggle. Reset switches are typically found near the base of the furnace, but check your manual for placement.
2. Turn the reset toggle to the ‘Off’ position to stop the flow of gas, then wait several minutes.
3. After some time has elapsed, turn the switch back to the ‘Pilot’ position to allow gas flow back to the pilot assembly.
4. Push and hold down the reset button as you use a match or long-handled lighter to ignite the pilot light.
5. Once a flame is established, release the button. Turn the switch to ‘On,’ then wait for the furnace to engage.

If you have any issues getting the pilot light lit or if your furnace still doesn’t blow warm air, it’s time to call our team at AAA Heating and Cooling.

#2: Dirty Air Filter

A dirty or clogged air filter is one of the most common causes of a furnace blowing cold air. 

According to a recent market poll, 82% of Americans fail to change their air filters monthly. If it’s been a while since your last routine HVAC maintenance, your home air filters could be clogged and grimy. Dirty filters can hinder proper airflow distribution throughout your residence, which could cause your furnace to overwork and overheat, resulting in cold air.

A dirty air filter may lead to several issues that can cause your furnace to shut down, including:

• Furnace fan malfunction: When your air filter is clogged, your furnace fan has to work much harder to pull air into the system, causing it to wear down quickly over time. 
• Damaged heat exchanger: A dirty air filter may prevent proper circulation in and out of the furnace, leading to a build-up of heat that may stress the heat exchanger. Too much stress may cause the heat exchanger to crack. 

Solution

Check your air filter for signs of dirt, grime, and debris. Replace it with a new one and stay up-to-date with your annual heating and air conditioning maintenance.

Don’t have a maintenance plan? No problem! Our installation team can set you up with one based on your needs.

#3: Clogged Condensate Lines

Some modern furnaces have condensate lines designed to remove moisture from the air. Over time, these lines can become clogged with dust and other particles. If your pipes have an abundance of debris, this blockage could disable the burners and lead to cold air coming from your furnace.

Additional signs your condensate line is clogged include:

• Water pooling below the unit
• Excessive noise when the unit is running
• Strange smells coming from your furnace

Solution

It’s best to call your residential HVAC services to diagnose and remedy condensate line issues. Our NATE-certified professionals will check the drain pan, unclog the lines, and clean them.

#4: Damaged or Defective Duct Systems

Cracked and damaged ducts can cause severe issues with your home heating. Gaps, holes, and tears can introduce cold air into your duct system and let warm air escape. Even if your furnace is in top shape, damaged ducts can distribute cold air throughout your residence. 

If you have recently had ducts replaced or ductwork done, there is also a chance that your ducts are leaking air due to being improperly sized. 

Air ducts may also become clogged over time. The EPA recommends having them professionally cleaned as needed and inspected before every winter season. 

Solution

Since ducts are intricate systems that are not always easy to get to, it’s best to let the HVAC experts handle this one. 

Minor damage might be easily fixed by professional duct sealing. If there is significant damage or your system is over ten years old, it might be time for a replacement.

#5: Thermostat Difficulties

Sometimes, the solution to a furnace blowing cold air is something as simple as the wrong thermostat setting. 

Always make sure your thermostat is set to ‘Heat,’ not ‘Cool.’ It may be obvious, but you never know if your spouse or roommate isn’t ready for indoor heating and is sneakily adjusting your thermostat behind your back. 

If your thermostat was recently installed, it may also be experiencing faulty wiring or is incompatible with the system. 

Solution

Check to ensure your thermostat is set to ‘Auto,’ not ‘On.’ If left in the ‘On’ position, your furnace will run continuously, even when it’s not producing heat. Try switching the batteries out to ensure full power. 

If this does not work, it is time to call the professionals at AAA Heating and Cooling. We specialize in heating and cooling equipment and after being in business for over 60 years, we’ve seen it all. We have experience working with older units as well as top-of-the-line, modern equipment. 

We’ll have your furnace working in no time so you can enjoy the comfort of your home again. 

AAA Heating and Cooling: Portland’s #1 Solution for All Your Furnace Frustrations

At AAA Heating and Cooling, we understand how brutal Portland winters can be and how you don’t want to be left without your heating system. 

We prioritize our clients’ time and promise always to have a quick solution for their furnace troubles. If this article has left you with more questions than answers regarding the query, “Why is my furnace blowing out cold air,” we have the answer!

Routine HVAC maintenance can avoid many issues with your furnace blowing out cold air. We cover everything from duct cleaning and retrofitting to thermostat installation and unit repair for residential and commercial clients. 

Allow our specialized team to prepare your home for year-round comfort with our maintenance services, or to rescue you from an HVAC emergency. 

Schedule an appointment for your Portland home furnace service today.