Why Is My Furnace Blowing Cold Air

Furnace blowing cold air

When the weather outside is frightful, you don’t need to rely on a fire to keep your home warm– that’s what your furnace is for. What should you do if, rather than keeping your house warm and cozy, your furnace is blowing cold air instead of producing heat?

Often, there is a fairly simple solution to fixing a furnace that is blowing cold air. Our Raleigh furnace repair company wants to keep you warm all winter by sharing the reasons your furnace is blowing cold air and the best ways to troubleshoot the problem and get it working properly again.

First, How A Furnace Works

When the temperature in your home goes below the temp programmed into your thermostat settings, the thermostat will signal the furnace’s internal control board to initiate the heating process. The furnace’s ignition switch is activated, the gas valve opens, and the draft fan turns on.

This combustion process warms up the heat exchanger, and flue gases are then released through the heat exchanger and the exhaust pipe. Room temperature air is then blown through the blower fan, where that air absorbs the heat from the furnace before it travels through the air ducts into your home.

If your furnace is operating correctly, the air being filtered into your home is now heated, providing a warm and comfortable home throughout the winter. Unfortunately, sometimes there can be a broken piece of the system that makes the entire process fail, causing your furnace to blow cold air.

If your furnace is failing to warm your home and is blowing cold air, it’s important to call a professional furnace repair technician for the safety and protection of your home.

Reasons Why A Furnace Might Blow Cold Air

A furnace that blows cold air can be either a simple or complex fix, as there are many reasons that this could be happening. Let’s explore some of the common reasons why your furnace may be blowing cold air.

Your Furnace Isn’t Warmed Up Yet

Just like when you run the hot water to take a shower, it can take a few minutes for the water to warm up before you get the desired temperature water out of the pipes. Similarly, if you notice your furnace blowing cold air after the thermostat turns on, wait a few minutes to give the combustion process time to heat the air through the vents. If after several minutes the furnace continues to fail to generate heat, then continue the troubleshooting process to try to figure out the source of failure within the heating system.

The Thermostat Is Set Incorrectly

If you notice your furnace is blowing cold air, check your thermostat first, and make sure it’s not set on cool. Whether someone bumped it, a child was playing near it, or you had a warm day not long ago and forgot to reset it, thermostat settings are often one of the common and simple reasons for cold air to blow from your system.

Your Thermostat Isn’t Compatible with Your Furnace

Thermostats are not universal to every furnace, so if you have a furnace that’s older than 10 years old, and you purchased a new smart thermostat, like a Nest, it may simply be that the furnace and thermostat are not compatible.

There are three types of thermostats:

  • Low Voltage: the most common type seen in newer systems;
  • Line Voltage: seen with electric baseboard heating and older systems;
  • Millivolt: often used in direct vent furnaces and mobile home systems;

Most smart thermostats are low voltage, so if you have a line voltage or millivolt, it will kick the system on, but it will blow cold air.

Similarly, consider the stage of your system. A single-stage system runs at full capacity all the time while a multi-stage (or stage two system) can run at low or high speeds. Some thermostats aren’t compatible with multi-stage systems. If you are unsure whether or not your new thermostat is compatible with your furnace, contact an experienced skilled furnace technician to schedule an inspection of your furnace and thermostat compatibility.

The Furnace Air Filter Is Dirty

A dirty air filter is a common culprit to a gas furnace heater blowing cold air. Your furnace’s air filter keeps dirt, dust, and allergens from getting into your furnace, but if it’s clogged, fresh air can’t get in at all.

When this happens, the furnace can overheat, shutting down the burners. The heater will still continue to kick on, but without burners to heat the air before it moves into the ductwork, your furnace will blow cold air.

It is recommended that homeowners clean their filters every 90 days or when it is noticeably filled with grey lint and dust buildup. If you are unsure of the preventative measures to take with your gas furnace, contact an HVAC professional for regular maintenance advice.

There’s Damage To Your Ductwork

Your ducts are responsible for transferring heated air from your furnace through your home. If your ducts are older and have cracks or leaks, cold air from your attic may be seeping into the ductwork and overpowering the warm air. Having your ducts cleaned and repaired will prevent leaks and ensure clean, comfortable air is traveling throughout your home without interruption.

Your Furnace Has Overheated

When a furnace overheats, the safety feature shuts the furnace off, which could be causing your furnace to blow air that is cold. This does not mean your furnace is necessarily broken- as a broken furnace will not activate the safety switch to stop hot air from blowing. When a gas furnace overheats, it’s usually because of a mechanical failure, dirt buildup, or the old age of the HVAC system.

If you detect signs of overheating, it can be very dangerous to your home and everyone in it. If the gas supply is on, but the furnace overheats causing the air to become trapped, it can lead to a fire, carbon monoxide leak, or even an explosion. Call an HVAC professional to look at why your furnace is blowing cold air, check the gas supply pipe, and determine if the heat pump is in working order or needs to be repaired or replaced.

The Condensate Line Is Clogged

If your vents are blowing cold air and you see a puddle of water around the surface of your furnace, it is likely that the condensate lines are blocked, resulting in it producing cold air. High-efficiency furnaces produce condensate, or water, that empties through a drain line. However, if there is water clogged in the condensate lines due to the buildup of dirt, mold, dust, or even ice, the overflow kill switch will activate, resulting in the furnace shutting down and water pooling or flooding.

The Pilot Light Is Out

If your furnace is in a drafty basement or other areas of your home where a small flame can easily be blown out, then it is possible that the source of cold air is a blown-out pilot light. This can be a problem with older furnaces, as newer furnaces have electric pilots that don’t need to be on all the time.

The pilot is a small flame that is continuously lit to keep the larger burners going when the heat kicks on. If the pilot light goes out, there’s no spark to light the larger burners, thus, no heat can travel through the ducts.

There Is A Problem With The Gas Supply

One of the more difficult issues with a furnace blowing cold air is that there may be a problem with your gas supply. Blocked gas lines, cracks in the gas valves, or a gas leak can cause the furnace to shut down and no longer produce hot air. Working with the gas supply is dangerous and should only be done by HVAC professionals with experience in working with natural gas furnaces.

Reaching Out To An HVAC Repair Company

If your furnace is blowing cold air, and simple fixes like checking the thermostat and changing the air filter don’t help, this is probably a job for professionals.

Trying to fix a furnace on your own can be significantly more dangerous and complicated than you realize. Even something that seems simple, like cleaning a gas valve or changing an oil filter can ultimately cause more issues than fixes if you do not know what you are doing. An improper repair can lead to more serious damage and even the risk of a fire.

It is always best to call an experienced furnace repair technician who can properly diagnose the problem, fix it fast, and have your furnace heating your home properly all winter long.

Schedule Furnace Repair for Your Garner Home Today

You rely on your furnace to keep your home cozy and comfortable through chilly Raleigh winters. Whether it’s blowing cold air or there’s something else wrong, an experienced HVAC technician from Bowman Mechanical Services can quickly spot the problem and restore heat and comfort to your home.

Give us a call at  919-772-2759 or fill out our contact form below to schedule service on maintenance and repairs.

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