What is a draft inducer motor?
Updated August 2026
A draft inducer is the small fan that spins up before a gas furnace lights, pulling combustion gases through the heat exchanger and pushing them out the flue. It runs a prepurge of roughly 15 to 60 seconds on every heat cycle, stays on the entire time the burners are lit, and runs a short postpurge afterward. Furnaces built before about 1990 relied on natural draft up a masonry chimney. Every mid-efficiency and condensing furnace since then uses this fan instead.
Where it is
Pull the upper access panel and look for a snail-shaped housing, plastic on condensing units and sheet metal on 80% models, bolted to the top or side of the heat exchanger with the flue pipe leaving one side. A thin rubber hose runs from a port on that housing to the pressure switch, a round disc with two wires. On a horizontal attic furnace the same assembly sits at the end nearest the vent pipe. You already know its sound: the rising whir that starts well before the whoosh of ignition.
What it does
Two jobs, and one of them is safety. The fan gives combustion gases a forced path outdoors so carbon monoxide never spills into the room, and the vacuum it creates closes the pressure switch, which is the control board's proof that venting works before it opens the gas valve. Dry bearings produce a whine or grind at the start of every cycle. A wheel loaded with soot, or a weakening motor, never pulls enough vacuum to close that switch, so the board waits, tries three times, and locks out with no heat and a flashing error code. Never jump a pressure switch to get through a cold night.
Maintenance
The inducer has no homeowner service interval of its own; it lives or dies with the annual tune-up. A technician should check amp draw, wheel cleanliness, and the pressure hose for cracks or trapped condensate during the pre-season visit covered in testing your furnace before winter. Soot on the wheel is a symptom rather than the disease, and it usually traces back to dirty burners, so hold that schedule too: how often to clean furnace burners. Expect 12 to 20 years of service, about the life of the furnace.
What it costs to replace
A replacement draft inducer runs $100–300 for the motor or full assembly, $300–600 installed by a technician.
OnOtto's photo scan identifies parts like this in your home and builds the maintenance schedule for you. See how the scan works.
Frequently asked questions
What does a failing draft inducer sound like?
Three noises, ranked by how often they show up. A metallic whine at startup that fades once the main blower joins in points to worn motor bearings. A rattle or buzz usually means a hardened mounting gasket or a bolt that backed out, a 10 minute fix. Scraping is the wheel touching its housing, and that one needs attention this week, because a seized wheel takes the entire heating cycle down with it.
My furnace runs a fan, then shuts off without lighting. Is that the inducer?
Often, but check the free causes first. That sequence means the board never saw the pressure switch close, so it never opened the gas valve. A blocked flue or intake pipe (bird nest, snow drift, matted insect screen) and a condensate trap full of water are the two most common reasons on a high-efficiency furnace, and clearing either costs nothing. If the vent is open, the trap drains, and the hose is intact, the inducer is moving too little air and needs replacing.
Is the draft inducer the same as the blower motor?
No, and the difference shows up on the invoice. The inducer moves combustion gas out the flue at maybe 100 cubic feet per minute. The blower moves 800 to 2,000 cubic feet per minute of conditioned air through your ducts and costs two to three times as much to replace. Burners firing but no warm air at the registers points to the blower. Burners that never fire at all point to the inducer or its pressure switch.
Can I keep running the furnace with a noisy inducer?
A whine you have heard for a week is not an emergency, but book the repair instead of waiting for the lockout, which always lands on the coldest night. What you cannot do is defeat the pressure switch to force ignition. That switch is the only thing confirming the flue is open, and bypassing it can vent carbon monoxide into living space. Keep a working CO alarm on every level no matter how the furnace behaves.