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Why is My Furnace Blowing Cold Air!?

I always find it interesting to observe the human nature of procrastination as it surrounds our HVAC systems. Many of us (myself included at times) wait until the very last second to turn our heat on for the first time, while others take a more proactive approach and have already tested the system by September 1st. I spoke to a homeowner recently who said they play a “game” of how long they wait to turn the heat on in their home, and joked that they attempt to last until they see their breath (NOT recommended!). Sometimes this first-of-the-season startup goes smoothly and warrants no follow-up action, but other times, things don’t go so swimmingly! Here are some first thoughts/actions if your system seems to be acting grumpy this Fall…

If Your Furnace is Blowing Cold Air

Many of our heating systems “take a minute” to ramp up and get to heating, but what does it mean if your system never catches its groove, and continues to blow “cold” air? Many times, this air that feels like it is cold, is really just room temperature air that FEELS cool since it is moving across your skin. If it is truly coming out cold (like air conditioning), take a look at whether your air conditioner is actually running, and whether you have the thermostat on the right setting. If you know you have your thermostat in the heating mode, and that your set point is above the room temperature, here are some common reasons that the air isn’t keeping you warm:

1. You Ran Out of Gas or Oil. Are you sure you remembered to fill the oil back up, or to call the propane company for a top-off at the end of last winter? Did you forget to pay your gas bill and they shut you down? This is a simple one to check, by looking at your oil or liquified petroleum (LP) tank levels, or checking to see if your gas meter is locked out. With most oil-fired systems, they won’t even blow cold air if you are out of oil (since the burner has to fire and warm up first), but it is always worth having a grasp on how much fuel you have during the heating season.

2. The Fan Switch is Set to “ON” on the Thermostat. Many people misunderstand the use of this switch, and get confused by the corresponding system behavior. For all intents and purposes, the fan switch should be left in the AUTO mode, meaning that your fan will only blow air during a call for heating (or cooling). When you (or your curious toddler) move this switch to ON, the fan will blow air continuously, regardless of whether or not the burner is heating, which can create discomfort and waste electricity. Homeowners who have invested in a high-efficiency air filtration system often turn this switch to ON for periods of time, to scrub the air and allergens in the house. Programmable thermostats can also do this on their own, based on your desires and schedules.

3. You Have a Burner Lockout. On many gas fired systems, the control board is capable of running the fan during certain types of burner failures, to protect the equipment from overheating. For example, if your system is going off on “high-limit” protection, the main control board will run the blower to cool down the heat exchanger, even after it stops firing the burner. Depending on how long the blower is set to run during this condition (sometimes permanently until a service person comes), you may experience room temperature air circulation. It never hurts to check your air filter, since a dirty air filter can reduce airflow, causing a high limit lockout.

4. You Need a Service Visit. Besides the aforementioned “dirty filter causing high-limit” example, there are dozens of other malfunctions that could cause your system to blow cold air. Some potentials are:
Other forms of burner lockout
Circuit board failure
Wiring issues
Thermostat failure
Boiler or circulator-related issues on a hydro-air system.

Due to the complexity and potential danger involved with fuel combustion systems, we strongly recommend that you reach out to a service provider to help with anything above and beyond a thermostat setting, changing thermostat batteries, or changing the air filter.

With such vast resources at our fingertips, DIY has become a huge part of all our lives, but should be left to shiplap installation and garage floor coating – not fuel burner troubleshooting. Don’t let Dad play superhero and end up hurting himself, or creating a situation far worse than the cold air that is blowing!

Call us today at 603.430.9414 or drop us a note here if you think you need a professional to take a look at your system.

Peter Robitaille
President, East Coast HVAC