Why Is My Furnace Blowing Cold Air?

When winter rages and the outside temperature drops, your home’s HVAC system is more critical than ever. There’s nothing more troublesome than noticing that your furnace is blowing cold air, whether continuously or erratically, in the middle of a brutal stretch of cold weather.

Luckily, there are a number of things you can do to get your home toasty again. We’ve rounded up some common grounds for furnaces to blow cold air, and how to best take care of the issue.

But, first, let’s take a brief look at how your furnace functions.

The moment the indoor temperature drops below the thermostat’s set temperature, the thermostat communicates to the control board inside the furnace to begin the heating process. The combustion procedure begins by turning on the draft fan. Next, the combustion warms up the furnace’s heat exchanger and, as a result of the combustion, flue gases are discharged outside by the heat exchanger and exhaust pipe.

A blower fan then drives room-temperature air past the heat exchanger. The cool air absorbs the heat and from there is forced through your home’s ductwork.

Now that you know how the heating process works, let’s further investigate what makes it blow cold air.

Are there improper fan settings?

Ever heard of Occam’s Razor? When troubleshooting, always begin with the easiest possible solution. In this instance, it’s the thermostat fan setting.

Check to see if the fan is set to “On.” If it is, then it will blow air constantly, whether or not the furnace generates heat. If your furnace is blowing only cold air, or hot sometimes and cold other times, then it’s probably a fan-setting issue. This is more usual on older thermostats with a fan control switch. These old-school switches can clearly be bumped into by an unaware adult or a child playing. (We’ve seen this occur when moving furniture past a hallway thermostat.)

In this case, the fix is easy: Move the setting from “On” to “Auto” and see if that takes care of the problem. The “auto” mode will stop your fan from blowing cold air when the preferred temperature is reached. It’ll also save money on your heating bills. Often, we likewise see homeowners set their thermostats to “fan” rather than “auto.”

Is the thermostat working properly?

Thermostats make our lives so much easier. They’re also one of the first places you should check if your furnace isn’t working properly. Since your thermostat links your home’s temperature setting to the furnace if it isn’t working as designed, your furnace could blow cold air simply because it isn’t obtaining the correct instructions from your thermostat.

Replacing the thermostat guarantees correct communication with your furnace to prevent cold air issues. Have your thermostat replaced by a certified HVAC technician and think about upgrading to a programmable or smart thermostat for improved command of indoor comfort and energy usage.

Note: When a thermostat battery runs low, it can cause the thermostat to just stop working. This is not a signal of an issue with your heating system or your home’s wiring. It’s just a dead or weakening battery. As the battery starts to weaken, so will the thermostat tasks.
Be sure you switch out thermostat batteries at least once every year.

Is there a faulty circuit control board?

In some instances, the perpetrator could be the circuit control board. This unit serves as the brain of the furnace, relaying instructions to its many components.

When the circuit control board accepts the heating cycled directive from the thermostat, it delivers signals to turn on the furnace blower and furnace burner. If the board is nonfunctional, it could turn the furnace blower on but not the burners. So if your furnace is not blowing hot air, it may be a result of the circuit control board not turning on the burners to heat the air.

There are a number of reasons why a circuit control board can crash, with the most common being a lack of regular maintenance.

Do you have cold air blowing because of a dirty air filter?

Concealed in the filter of your heating system are dirt and debris. If you aren’t cleaning it routinely, this will gather over time, leading to issues with your heating system’s efficiency. As a consequence, your furnace blowing cold air could simply be a result of a clogged filter. If this is the case, the cold air from inside your house will fight to pass through it and into the furnace. This indicates you have an inadequate amount of air to heat and redistribute and the outcome is your furnace blowing cold air.

As we’ve discussed in previous blog posts, your furnace air filter is a critical factor that impacts the efficiency of your heating system. We recommend changing furnace filters at least once every three months, but sometimes, if someone in your household suffers from allergies, or the home has at least one pet, you just might want to be sure they’re replaced more often.

If you’ve forgotten about it, now is the time to get rid of that dirty air filter! And always remember to replace the filter with a properly sized replacement.

Is the pilot light extinguished?

A pilot light is a small gas light that burns nonstop to ignite a larger burner, such as a furnace. However, this light can be doused if there is a draft, a dirty valve, or a defective thermocouple (a safety device that shuts off the gas when no pilot light is detected.)

Look for a pilot light on models that are 20 or more years old as later HVAC systems don’t normally have this feature.

For many homeowners, relighting a pilot light is an uncomplicated process. Most appliances will come with the directions affixed. If the light persists in going out after following the instructions and you’re certain there’s no draft blowing it out, a damaged thermocouple could be to blame. Most homeowners choose to call in a furnace technician to appraise and replace this part.

Do you have a faulty flame detector?

Today’s home heating units are forward-thinking, beyond using pilot lighting to initiate ignition. Instead, they employ a flame detector to instigate the heating. But what if your heater’s flame detector is dusty or filled with dirt and grime? Then, the heating process will not be started, meaning unheated air will blow from the unit.

This shortcoming may be remedied by simply dusting off the ignition sensor. Or you might want to depend on our team of HVAC experts to sanitize the flame detector and reestablish the heating process.

Is there a problem with the gas supply?

Furnaces need a constant supply of gas to the burners to generate heat. If the gas supply is deficient, the furnace will simply stop running as a safety measure, hence blowing out cold air. To consider this possibility, double-check that the gas valve is turned on by making sure the valve lever is parallel with the gas supply line. If there is still no gas going to the furnace, it’s a sign of an issue somewhere in the system.

While it’s certainly possible to troubleshoot gas lines, this kind of repair is best left to the experts. The risks are high and too many things could go awry.

Is your furnace overheating?

When your furnace overheats, there’s a safety device that will shut your furnace down. So, not only will your furnace be blowing cold air for the time being, it’ll actually shut off.

There are several reasons your furnace might be overheating (besides a clogged filter).

  • Dirt buildup: If your air filter was clogged, odds are dirt and debris worked their way into other segments of your furnace. If that dirt is affecting components, such as the blower, it can cause your unit to overheat.
  • Mechanical failure: Since a furnace undergoes wear and tear, it’s conceivable for it to overheat because one of the moving parts isn’t functioning correctly, if at all. This may be the basis of your furnace problem, especially if your unit is somewhat older.
  • Age: As the furnace ages, it won’t perform as well, as is the case with most such equipment. Furnaces normally last around 15 years. Even with the best preventative maintenance program, it can’t last forever and might begin overheating if specific parts are no longer performing as intended. Typically, the furnace burner, the flame sensor, or the gas supply pipe are at fault.

Is the condensate line clogged?

The latest state-of-the-art furnaces are engineered with condensate lines that transport water away from the furnace.

A clog in the condensate line will stop your furnace from igniting.
And no ignition means nothing but cold air coming through the vents. There might also be a problem with your condensate drain lines, but, if this is the case, an HVAC technician will be better able to tell you precisely what the problem is.

Are the cracks in the ductwork?

Cracks or holes in the ductwork might well be the cause of cold air emissions. Any of these tiny or large openings in the ducts let hot air escape while allowing cold air in.

Even with a well-functioning furnace, such leaks restrict hot air flow. Moreover, cold air seeping into the furnace ducts cools down the lingering hot air. If this takes place, your furnace will be blowing cold or somewhat warm air in place of hot air.

The issue can be fixed by finding the cracks and sealing them to stop hot air loss or cold air from going into the ductwork.
It’s worth considering a professional HVAC provider to make sure you catch and seal every last crack in the ductwork.

Is there a crack in the heat exchanger?

Your furnace blowing cold air could be a result of a cracked heat exchanger. If this is the issue, your household is at immediate risk of carbon monoxide poisoning. Contact your HVAC professionals a.s.a.p.!!!

Routine maintenance can prevent future problems

As is often the situation with home appliances, regular maintenance is the secret to preventing future problems. Preventative care can help lower the prospect of a problem arising, in addition to flagging an issue before it results in a shutdown. It’s advised to follow the maintenance steps in the owner’s manual, as well as these other preventative tips.

  • Consistently replace air filters. We cannot overstate the significance of replacing your filters every 90 days or when they appear dirty.
  • Check venting systems and accessory units. Make sure that pipes, humidifiers, electronic air cleaners, and other such equipment are secure. Watch for signs of water leaks.
  • Clean the unit’s interior and exterior areas. Be sure the blower wheel or fan motor and blade, plus the burner, are clean and free of rust or corrosion. Double-check the electrical connections and controls. If you’re not comfortable with HVAC systems, this is best left to the professionals at Schultheis Brothers.

Have Schultheis Brothers come to take a look

If you’ve read the various tips mentioned, and you still can’t discover the source of the problem, call the professionals at Schultheis Brothers to inspect your furnace or HVAC system. Don’t attempt to repair a furnace yourself!

The friendly professionals at Schultheis Brothers can detect and repair the problem on any make or model of furnace. We can also perform preventative maintenance after the repair is completed to prevent this from occurring again. They can also offer other insights and help decide whether it’s time to install a new heating system. An HVAC professional can also provide information about various heating solutions, such as employing a heat pump rather than a traditional furnace.