What’s Causing Your Noisy Furnace?

Woman unable to sleep covering ears with pillow
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A noisy furnace is not only annoying; it can also be the sign of a serious problem. Here’s a look at the sources of your furnace-related sounds:

Before You Begin

Turn off the power and gas to your furnace if you notice loud or unusual sounds. Continuing to use a malfunctioning furnace can cause serious damage to the unit and require expensive repairs.

Identifying Furnace Sounds

Use this list of common furnace-related noises and their possible causes to better describe the problem to your pro:

  • Scraping. A scraping or metal-hitting-metal sound comes from three potential sources:
  • A loose blower wheel. Blower wheels can come loose and hit the blower housing, causing a scraping sound. If left long enough, a loose blower wheel can damage itself and the housing.
  • A broken blower wheel. A broken blower wheel will vibrate in its housing, resulting in squealing, scratching and banging sounds.
  • A broken motor mount. A broken motor mount causes the blower wheel to drop and rattle against the housing. Shut your furnace off if you have a compromised mount.
  • Thumping. Thumping and vibrating sounds are the result of an unbalanced blower wheel. The motor itself can also become out of balance. Have a pro take a look to avoid further damage to your furnace.
  • Humming. If you hear humming but your furnace is functioning correctly, you likely have a loud transformer. Furnace problems and humming are sometimes related to a bad interior fan or capacitor.
  • Squealing. A lack of lubricant or a loose fan belt can cause high-pitched squealing. Applying oil or tightening your blower belt should stop the squealing. Call a pro if you’re unsure how to perform either of these jobs.
  • Banging. The start-stop cycle of your furnace fan can cause the sheet metal siding to bend inward, resulting in a banging or popping sound. This could be the sign of an undersized duct, closed vents or a clogged filter.
  • Rumbling. Low rumbling can indicate a problem with your burner. Turn off your furnace and call a professional if you notice a constant rumbling.

Fixing Your Furnace

It’s a good idea to call a professional if you’re experiencing problems with your furnace. Tackling most furnace repairs yourself can damage your unit and lead to home-threatening problems like gas leaks. Fortunately, not all furnace fixes require the work of a professional. Here are two repairs that you can tackle on your own:

Replacing a Filter

Installing a new filter is a simple way to improve your furnace’s efficiency and address some unwanted sounds. Here’s a quick how to:

Check your Flue

Your furnace’s flue is what vents harmful gases like carbon monoxide away from your home. Changing your filter presents a good time to ensure your flu is free of any rust, corrosion or other deterioration.

  1. Choose your filter. Filters vary in terms of lifespan and effectiveness. Low-quality filters will last around 30 days but come in a multi-pack. Middle-tier filters last 90 days, and some high-end options offer washable models, which last indefinitely.
  2. Turn off your furnace. Set your thermostat to “off” before installing your filter.
  3. Open access panel. Your furnace’s access panel is located on the side or toward the bottom of the unit. Loosen the panel’s screws, lift up the clips, tilt the top toward you and lift up the bottom.
  1. Remove the old filter. Once the panel is gone, you should be able to see the blower fan and motor. Pull out the old filter and slide in the new one. Be sure to follow the arrows on the filter that mark the flow of air.
  2. Vacuum the furnace floor. Dirt, dust and grime can collect on the floor of your furnace. Quickly run your vacuum over the area to remove any buildup of gunk.
  3. Clean your floor vents. You can also quickly vacuum your floor vents to improve the effectiveness and lifespan of your furnace and filter.
  4. Replace the access panel. Put the access panel back in place and turn on your furnace.

Oil Your Blower Motor

A lack of lubrication can diminish your furnace’s effectiveness and cause unwanted noise. Adding oil to your furnace requires some mechanical know-how. Call a pro if you’re unsure about tackling this job.

Here’s a guide to help you lubricate your blower motor:

  1. Turn off the power. Cut the power to your furnace by turning off the circuit breaker at the main electrical panel.
  2. Open the access panel. Locate your access panel and loosen the screws to remove it.
  3. Remove the blower motor housing. The blower motor housing is located near the base of the furnace. Remove the bolts holding the housing in place and carefully pull it out of the furnace. Be sure not to stretch the motor’s wires. Leave the motor just outside of the furnace.
  4. Remove the motor. Remove the set screw on the side of the housing with an Allen-head screwdriver. Pull the motor out of the housing.
  5. Add the oil. The oil ports on the motor are usually marked with plastic or metal plugs. Remove the plugs and squeeze two three drops into the ports.
  6. Re-install the motor. Replace the motor and the access panel.