Modern furnaces require two blower motors: one for the house blower and one for the inducer blower. The inducer fan (or draft inducer) creates negative pressure in the combustion chamber, pulling exhaust gases away from the furnace and out of your house. This "draft" not only ensures your furnace operates safely but also improves efficiency by ensuring clean combustion.
Of course, the inducer motor is a mechanical part, and many inducer motors will fail before the rest of the furnace reaches the end of its lifespan. Since your furnace contains a pressure switch to confirm proper draft, a faulty inducer will likely prevent your furnace from operating at all. While you'll need to replace your inducer once it goes bad, it can be helpful to know why they fail in the first place.
The Most Common Causes of Inducer Failure
Most furnace inducer motors are maintenance-free designs. These motors lack oil ports and keep their internal bearings inside sealed chambers. This design has several advantages, including reducing the likelihood of oil contamination and eliminating the need to add oil. However, it also has a significant downside: if the bearings wear out, you typically cannot lubricate and repack them.
Inducer motor failures often occur due to normal wear and tear. As the motor ages, the internal oil loses its lubricating properties. This breakdown causes friction to increase, creating more heat and ultimately causing the motor to wear out. You'll usually notice problems from the inducer motor before it eventually stops working at all.
Excessive internal dust or soot is another potential cause of premature failure. Combustion issues resulting in excess soot build-up can cause an accumulation on the motor, causing it to work harder and overheat. You may also notice problems if your furnace is in a dusty environment or if an issue with your air filter allows debris to enter the furnace's cabinet.
The Early Warning Signs of a Bad Inducer
Your furnace's draft inducer is a relatively straightforward electric motor and blower. As it begins to fail, you'll generally hear the sounds caused by increasing internal friction and wear. Typical noises include tapping, grinding, squealing, or whirring. Since the draft inducer comes on before the house blower, you may hear these sounds before your furnace ignites or air begins moving through your vents.
The problem will eventually progress to the point where the motor will no longer induce sufficient draft, at which point the pressure switch will fail to close. Your furnace will not turn on or produce heat with the pressure switch stuck open. Never attempt to bypass the pressure switch since it's a critical safety feature of any modern furnace.
If you hear your furnace producing these noises, it's a good idea to contact an HVAC repair technician as soon as possible. Locating and addressing the cause of inducer motor problems may allow you to repair the issue before the motor fails and forces you to purchase a replacement.