January 17, 2024

Whenever your furnace begins blowing cold air, it can cause anxiety and panic, making you wonder what’s wrong. Some of the problems are simple to resolve yourself or with maintenance while others require proper repair. Consider these seven common reasons your furnace may blow cold air.

1. Your Thermostat’s Fan Setting

A thermostat is the major control for your furnace, initiating and terminating heating cycles. However, it also works in conjunction with the control board to control the function of the circulating fan.

Most thermostats have two options for the fan setting; On and Auto. While it makes sense to set it to On, this is actually not the correct option. Rather, when you set the fan to On, it runs all the time, regardless of whether the furnace is cycling. The result is that it will circulate unheated air through your supply vents.

2. Dirty Flame Sensor

Modern furnaces use an electronic ignition rather than a standing pilot light. To ensure that the furnace isn’t allowing fuel to flow in without burning, it has a flame sensor. However, the flame sensor can become dirty from the byproducts of the burning fuel. When it does, it may not sense a flame burning and will shut down the gas flowing to the burners, inhibiting heat production. A technician will clean the flame sensor during routine furnace maintenance to ensure that it’s sensing heat properly.

3. Airflow Restrictions

To operate properly, a furnace relies on sufficient air flowing through the system. When air can’t flow properly, heat builds up in the system, causing short cycling. However, during an overheating situation, the circulating fan will continue blowing to reduce the heat in the furnace, making it feel like it’s blowing cold air.

The most common airflow restriction is a clogged air filter. Being this removes airborne contaminants, it’ll need routine changing to continue allowing enough air to pass through. For most 1- and 2-inch air filters, you can expect to change the filter every 30 to 90 days. Other airflow restrictions include contaminant buildup further in the system, which a technician will clean during routine maintenance.

4.Overheating Issues

Airflow restrictions aren’t the only issues that’ll cause overheating. A new furnace that’s overheating may be oversized for your home. If your system is short cycling for some reason, this can also cause it to overheat. It may also happen when there’s an issue with your exhaust, preventing it from exiting the system efficiently. Finally, there could be a mechanical failure that’ll allow heat to build up. The most common is a blower motor that’s wearing out.

5. Clogged Condensate Drains

High-efficiency furnaces will produce condensation, which drains away from the system using the condensate drain. However, that drain will eventually clog from airborne dirt and debris along with some contaminants from within the furnace. When this happens, the furnace has a safety switch to prevent damage to the unit. The best way to keep this clear is to stay current on your annual maintenance for both your furnace and central air.

6. Leaking and Improperly Insulated Ductwork

Every furnace relies on the system’s ductwork to transport the heated air around the building. That ductwork is not always well sealed when it’s installed, and may develop leaks over time.

Leaks in the ductwork both allow heated air to leak out and cool air to leak in. If your ducts aren’t well insulated where they go through cold areas, it’ll transfer some of the heat to that cold air. The result of both is cooler air coming from your supply vents.

7. Faulty High Limit Switch

The high limit switch monitors the temperature at the heat exchanger and shuts the furnace down to prevent damage. However, the high limit switch can become faulty over time, requiring a replacement. High limit switches can become faulty in both directions, sensing too low of temperature or too high of temperature. Either is problematic for your system and that is why a technician will test the switch during routine furnace maintenance.

People around Arlington Heights have trusted IBBOTSON Heating & Air Conditioning Co. to keep their furnaces running well since 1946. Our award-winning team provides AC and heating maintenance, repair and installation together with indoor air quality solutions. Call to schedule furnace repair or maintenance with one of our NATE-certified technicians today.

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