What Is a Furnace Inducer Motor and Why Is It Important?
The inducer motor is a necessary component of modern, gas-powered, high-efficiency furnaces. If it's not working, the furnace won't start.
The inducer motor is a fairly recent piece of equipment on gas furnaces, so it isn’t surprising many homeowners don’t know why it’s there or what it does. Because it’s integrated into the furnace’s control system, it can cause real problems if it malfunctions, so it’s good to be aware.
“Since a modern furnace cannot run without an inducer motor, it will usually shut itself down if the inducer motor fails,” says John Gabrielli, owner of Air Temp Solutions.
All in all, furnaces have become more sophisticated in the last half century. The forces driving the improvements? Concerns about atmospheric emissions and fuel efficiency.
Modern high-efficiency gas furnaces can convert almost 100% of the energy potential of the fuel they burn into heat while releasing negligible amounts of toxic gases. Compare this to gas furnaces of the mid-20th century, which filled the air with toxic fumes and were often less than 60% efficient. Yes, they wasted 40% of their energy.
Inducer motors didn’t even exist until Congress mandated minimum efficiency ratings for furnaces in 1992. Today, they’re standard equipment on most new furnaces.
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What Is a Furnace Inducer Motor?
“The inducer motor runs a fan which provides air for combustion within a furnace and also pushes the exhaust gases out of the flue,” Gabrielli says. For this reason, HVAC pros often refer to it as a draft inducer. Don’t confuse it with the fan that circulates warm air through the ducts. That’s called the blower, and it isn’t the same thing.
Combustion in a gas furnace takes place in a sealed chamber. Many standard-efficiency models with an Annual Fuel Efficiency Ratio (AFUE) of 80% feature vents that allow air to circulate naturally, and a chimney-like vent to exhaust combustion gases. That isn’t true of high-efficiency furnaces, also known as condensing furnaces.
“Modern high-efficiency condensing furnaces tend to take more heat out of the exhaust gases,” says Gabrielli. “Because the gases are cooler, they won’t rise, so an inducer motor is necessary to push them out.”
Besides getting rid of exhaust gases, a draft inducer also draws air into the chamber to feed the burner and promote more complete combustion. That also improves efficiency.
How To Tell if Your Furnace Inducer Motor Is Failing
Strange tapping, humming or whirring noises from the inducer motor are usually the first signs of a problem. As the problem progresses, the blower may fail to turn on, and eventually the entire furnace will shut down.
If the furnace doesn’t come on, two simple tests can verify whether the inducer motor is the culprit.
After turning off the power to the furnace and using a voltage tester to ensure the power is off, remove the furnace door, reach in and touch the blower motor to see if it’s hot. If so, that indicates it tried to start, but can’t. Next, try spinning the blower wheel (HVAC pros call this the birdcage) to see if it spins freely. If it doesn’t, that’s another sign of a faulty inducer motor.
What Happens if the Furnace Inducer Motor Stops Working?
The furnace control board is programmed to turn on the inducer motor about a minute before the burners ignite and the blower starts. If the inducer motor doesn’t come on, the furnace won’t send the necessary signal to the burners and blower and won’t start.
What Causes a Furnace Inducer Motor To Go Bad?
When an inducer motor stops working, the problem could be debris inside the housing, a mechanical problem with the bearings or the motor windings, or an electrical issue. It’s easier to check for mechanical problems before doing any electrical testing.
Turn off the furnace power switch or, if you can’t find it, switch off the breaker that controls the furnace in the main electrical panel. Remove the furnace cover and find the inducer motor (check your owner’s manual if necessary). Put on protective gloves to avoid nicks and try spinning the fan blades.
If they don’t turn freely, look for debris that might be preventing them from moving, because sometimes the problem is as simple as a rodent’s nest. It’s also possible the fan is momentarily stuck and will spin freely once you put a little pressure on it.
If the fan stays stuck, and you don’t find any evidence of pests, the bearings or some other mechanical component inside the motor may be worn out. If the fan spins freely but the motor doesn’t start up, it’s probably an electrical issue. The start capacitor for the motor could be worn out, and that’s simple for an HVAC tech to diagnose and replace.
There could also be a malfunction in the control board, another problem a pro with the right equipment can diagnose.
How Much Does It Cost To Replace a Furnace Inducer Motor?
According to Gabrielli, the cost can vary greatly depending on the model of the furnace, the availability of parts, and the company you call to make the repair. “All of these factors considered, the repair can be anywhere from $300 to $1,800,” he says.
If the culprit turns out to be the capacitor, the repair probably won’t cost much more than $250. If the control panel is causing the problem, you’re probably looking at $500 to $900.
About the Expert
John Gabrielli’s father was in the HVAC trade, and he grew up to master the trade himself. He owns Delaware-based Air Temp Solutions.