Your furnace exhaust fan, also called the inducer fan, is a crucial part of venting your furnace properly. It vents the exhaust that's created during the combustion process to the outside to keep your home safe. Noises coming from the inducer fan or inducer motor can indicate a problem that needs to be fixed.
Damaged Motor Bearings
The inducer fan motor includes bearings that can go bad and cause a very loud, constant noise. If the bearings are unsealed, they need to be oiled every six months or so as preventative maintenance. When you don't oil them, the bearings can go bad to the point that adding more oil won't help. They need to be replaced.
Video of the Day
Sealed bearings don't have to be oiled, but they can still go bad. When this happens, they also make a loud, constant noise. If you suspect the bearings are the issue, have them checked out and replaced immediately. They can generate a lot of heat and potentially cause a fire.
Incorrect Inducer Fan Position
Proper installation of all HVAC system components is important to keep everything working correctly. If the inducer fan motor or the entire furnace is installed with an incorrect pitch, you might hear a sloshing water sound coming from it. The motor housing has a drain that removes water, but it can't drain properly if the angle is incorrect. Correcting the installation angle can allow for proper drainage.
Debris in the Motor
Debris can fall into the inducer motor and cause noises. A similar issue is an animal building a nest in the motor. When the fan kicks on automatically, you'll likely hear the noise for the first 15 to 20 seconds of it running. The sound often stops once it gets going, but you'll hear it again the next time the fan kicks on. This can happen if the debris starts to go out of the exhaust pipe but then falls back in when the fan stops running.
If this happens, you'll need to have the inducer motor cleaned out completely. Use a flashlight to inspect the motor and find the debris. If you don't feel comfortable doing this, hire an HVAC professional to clear out the debris. The vent line might also need to be cleared if the debris is in that area. If the debris gets bad enough, the inducer motor might not be able to turn at all.
Clogs in the System
Clogs can happen in areas in and around the inducer motor, which can cause unusual noises. The exhaust vent, intake, or heat exchanger are all areas susceptible to clogs. The inducer motor might work harder to try to push the area out through the clogged sections, which makes it sound louder than normal. These clogs need to be cleared, as they can cause more serious problems within the unit.
Loose or Rubbing Components
Sometimes, parts can rub together because of vibrations or loose components. For example, the inducer motor might vibrate so much that it touches other components, creating a metal-on-metal noise. Sometimes, the wheel inside the motor rubs against the housing and makes it noisy. In other cases, the wheel can come loose, or fins from the wheel can fall off and bang against other parts.
Tightening loose components can help remedy the noises you hear. You might need to replace components if parts are missing or rusted. Having regular HVAC checkups can help prevent parts from rubbing, becoming loose, or otherwise having issues that cause noises in your furnace.