Few things are more unsettling during the chilly months than discovering that your furnace is running, yet it’s blowing out cold air instead of the comforting warmth you crave. Before you panic and envision shivering through the winter, let’s delve into some common reasons behind this perplexing issue and explore potential solutions to bring back the cozy heat you deserve.

Thermostat Woes:

Begin your troubleshooting journey by checking the thermostat settings. It’s not uncommon for the thermostat to accidentally be set to “cool” instead of “heat,” or for the temperature setting to be too low. Verify that the thermostat is in heating mode, set to your desired temperature, and give it a few moments to see if the warm air returns. Another common mistake homeowners make is confusing the “fan ON” switch with the furnace never shutting off and blowing cold air. Often, HVAC professionals will set up the furnace fan to run all the time as this helps even out the temperatures throughout the home.

Clogged Air Filter:

A clogged or dirty air filter can impede proper airflow, causing your furnace to move less air than it is designed to. In many cases, if a furnace isn’t moving enough air, it will cause the furnace to overheat. There are safety devices inside your gas furnace called ‘high-limit’ or ‘limit’ switches. There may be one limit switch or multiple depending on the equipment. If the limit switch trips, it will automatically shut off the burner but keep the fan running in an effort to cool the furnace down. Once the limit switch cools down, the furnace safety circuit will close and it will start the process over. Over time, filters accumulate dust and debris, restricting the system’s efficiency. Check your filter and replace it if it appears dirty. Regularly changing filters is a simple yet effective way to ensure your furnace operates at its best.

Pilot Light or Ignition Issues:

If your furnace is equipped with a pilot light, ensure it is lit. Modern furnaces typically use electronic ignition systems. In either case, if there are issues with the ignition, your furnace may run but fail to produce heat. There are many reasons a furnace may have ignition issues. For instance, improperly installed venting or a clogged condensate drain could cause an ignition issue. Consult your furnace manual for guidance on relighting the pilot light or, if the issue persists, it may be time to call in a professional.

Gas Supply Problems:

A lack of gas supply to your furnace can result in cold air blowing through the vents. Check to see if other gas appliances in your home are working. If they are not, there may be an issue with your gas supply. In such cases, it’s crucial to contact your gas utility provider immediately to address the issue.

Improperly Sized Furnace:

As discussed above in the filter section, poor airflow is a huge problem for your furnace. Aside from a clogged filter, another cause of poor airflow could be an oversized furnace. When sizing equipment for a home, a contractor must calculate what size furnace the home needs based on a load calculation. Then the contractor must size the furnace accordingly. A common mistake in retrofit/replacement is for a contractor to use a rule of thumb and miss important factors. For instance, if the customer had a 100k BTU furnace in place, many contractors will just replace the unit with exactly what is there. The truth is, bigger isn’t better. If the ductwork in the home is only capable of moving 80,000 BTUs of heat, then a 100k unit will likely cause high static pressure in the duct system. The result is less airflow through the furnace, which will cause the high-limit switch to trip. As described above, when the high-limit trips, the blower stays on while the gas valve turns off, which emulates a ‘blowing cold air’ situation.

Blocked Air Ducts:

Obstructed or blocked air ducts can hinder the distribution of warm air throughout your home. Check for any obstructions, such as furniture or debris, and ensure that all vents are open and unobstructed. A common misconception is that you should shut the vents in the basement to push more air upstairs in the summer or vice versa in the winter. The truth is, no residential HVAC contractors design the system with extra ducts. Closing off vents can cause static pressure and lack of airflow, which can result in the equipment tripping on high limit. Similarly, putting furniture over or in front of large return grilles can cause a similar problem.

So what can be done if my furnace only blows cold air?

Discovering that your furnace is blowing cold air can be a chilling experience, but fear not – many of these issues have straightforward solutions. By systematically checking thermostat settings, inspecting air filters, and addressing ignition or gas supply issues, you can often restore your furnace to its warm and toasty functionality. If troubleshooting on your own doesn’t resolve the problem, don’t hesitate to seek the expertise of Vectra Mechanical. Remember, a well-maintained and efficiently operating furnace is key to staying warm and comfortable throughout the winter months.