The Unfiltered Blog

February 6, 2020

Why your furnace or ducts are making strange noises

By Steve Terry, Vice President of Construction and Service

This time of year, we get lots of questions about the noises your furnace or air ducts are making. The most important thing you should know is not to ignore it or wait for it to go away — you’ll only allow the issue to get worse. Here’s what you should listen for.

What do different sounds mean?
Any noise is a red flag, but different sounds mean different things. Here are the most common ones we hear about:

  • A pop, bang or clunking noise in the duct: This is called “oil canning” and typically happens when the furnace shuts off because the air in the ducts loses pressure. It could mean your ducts are old and need some reinforcement.
  • A high-pitched whistle: This usually means you have dirty filters.
  • A humming, buzzing or lower-pitched whistle: This one depends on several things — the speed of the blower on your furnace, how your duct work was hooked up, or how many registers you have and how many of them are shut. If you close too many registers, you’re cutting off air movement, which could reduce the life of your system’s components.
  • A ticking, rattling or flapping noise: This probably means a wrapper or something similar got into the ducts.
  • A squeaky or squealing motor: This often means imminent failure because a bearing or winding is about to give out. If this is ignored and your motor seizes up, additional damage could be done like tripping breakers or even destroying the circuit board. Waiting to call a professional could mean your furnace goes out when you need it most.

One thing to keep in mind is that there are some noises that are normal, like the click of the gas valve/igniter. Older systems’ sounds will be louder than newer systems, so if you’ve just updated your system or moved to a newer home, you may hear (or not hear) things you’re not used to.

What should I do if I’m hearing these noises?
Record the noise on your phone and note what phase of operation the system is in when it’s happening. The cycle starts with the inducer coming on, then the burner, then the blower. Turning off will happen in a different order — burner, inducer, then blower. If it’s a motor issue, start-up and shut down are the two main times you’ll hear noise.

It’s best to call someone sooner rather than later to check it out. We often talk to people who have been hearing a noise for a week or more and hoped to just make it through the season before doing anything about it. Inevitably, they call at 3:00 a.m. in a panic because the motor went out, and now they may be in the back of the line for service in a queue of customers who have done the same.

If you’re hearing problematic noises — especially during a time when your heat or air conditioning will be running regularly — remember that the more it’s running, the more chance there is for it to fail. Don’t put yourself in a bad situation by ignoring it and hoping for the best.

If you’ve heard these noises in your home lately, it may be time to do something about it. Call us at 515-244-8911 or fill out our online form.