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Warning Signs Your Furnace Motor May Need to be Replaced

Furnace MotorNo one wants to suddenly be caught without heat, especially in a Minnesota winter. Your furnace motor, of course, is a major component of your heating system and you’ll want to be sure it’s in top running condition. Luckily, that’s usually pretty simple.

How Furnace Motors Work

There are two basic types of furnace motors. 

  • A direct drive motor is connected directly to the furnace’s blower wheel. It’s the most common type of motor in modern furnaces, with over 99% of gas furnaces being direct drive.

  • Belt drive motors are less common on residential furnaces. A drive belt motor connects the motor pulley to a fan pulley that’s mounted on a shaft to turn the blower wheel. Drive belt motors are common in commercial HVAC heating products.

Both types of motors are built to last up to 20 years with minimal maintenance required. The primary reasons that a motor might fail before its time are overheating and excess moisture.


The most common cause for motor failure is overheating. If your motor overheats, it damages the electrical windings and overheats the bearings, which causes an electrical short and/or a bearing failure. The bearing is lubricated with oil, which will typically last the life of the motor. But if the motor overheats, the oil breaks down and the loss of lubrication causes the bearing to bind and ultimately seize up.

The most common reason a motor will overheat is poor airflow within the motor due to dust and dirt. Even in a brand-new home, if the furnace was run during construction, the dust from sheetrock can infiltrate and kill the motor. Even if the damage isn’t that severe, if left unattended, the construction debris can significantly shorten the life of the motor.

Overheating can also be caused by operating your furnace at too high or too low a voltage. While this isn’t a common occurrence, it can happen, especially if you’re located in a rural area or are running a home generator.

Excess Moisture

Excess moisture is the next most common reason for motor failure. The culprit is usually water dripping from above. There are several ways this can occur. For example, a condensate leak in the A-Coil drain system or a frozen coil that drips as it defrosts. Where sealed combustion is ducted to the furnace, if not ducted properly, condensation can form and can drip into the vestibule and find its way to the motor. If a humidifier is installed above the furnace, it can leak if not properly maintained and cause water to drip on the motor. Regardless of how it infiltrates the motor, moisture can short it out, requiring repair or replacement.

Read our Complete Guide to Buying a New Furnace

What to Watch — and Listen — For

Keeping your motor running smoothly and efficiently shouldn’t take a great deal of effort. Just follow these simple guidelines:

  • Check and replace your filter regularly. It’s a good idea to check it monthly and replace it as soon as you see it getting dirty. At a minimum, replace it every three months.

  • Have your furnace inspected annually or bi-annually. Not only can your HVAC professional identify any concerns early on, but you’ll ensure that your system is running safely and efficiently.

  • If you hear something odd or unusual in your furnace’s operation, have it checked out right away. Early detection is key to minimal damage and repair costs.

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