What Causes Squealing Furnace Noises?
Last November a woman out on Williamson Valley Road called about her furnace squealing every time it came on. She’d already changed the filter (good, that’s the first thing I’d have told her) and it didn’t help.
Her words were that it sounded like a grocery cart with a bad wheel. Which, yeah. That’s about what a dry bearing sounds like.
The Two Things I Ask Over the Phone
First one’s the filter. Most people have done it already by the time they call me, but I ask anyway, because a filter that’s really packed can make the blower strain and whine. Prescott’s dusty. If you’re near a dirt road, a cheap 1-inch filter can be gray in six weeks or so.
But filter noise is usually more of a whistle than anything. If a clean filter doesn’t change it, I quit worrying about the filter.
The second thing I ask is when it starts. If the squealing starts right as the thermostat clicks, before you get any warm air, I’m thinking inducer motor, which is the little fan that clears the flue before the burners light. If it starts a minute or so later, when air starts coming out of the vents, it’s probably the blower. Hers was the second one.
Finding Where the Noise Is Coming From
Furnace noise is tricky to track down because it travels. It goes through the sheet metal and down the ducts, so wherever it’s loudest in the house usually isn’t where the problem is. Hers was loudest in a back bedroom, nowhere near the furnace.
I had her run it while I stood by the cabinet and listened, then I shut it off and pulled the blower door. The blower motor was hot, and when I grabbed the shaft there was a little wobble in it. There shouldn’t be any. That’s a sleeve bearing that’s dried out.
No belt on hers, it was direct drive. Older belt-drive furnaces can do the same squealing at startup when the belt’s glazed or loose, though, and honestly that’s the better problem to have because a belt’s cheap.
Fixing It and How Long That Takes
Some older motors have oil ports on them, and a few drops of 20-weight non-detergent oil can get you through another season. Hers didn’t have any. Most motors from the last twenty years or so are sealed, so once the bearing goes you’re buying a motor.
I put in a PSC motor that matched her old one, and a new run capacitor while I was in there. A weak capacitor makes a motor run hot and could cause the breaker to trip, and they don’t cost much. All in, a furnace repair like that is about an hour and a half. Two if the blower wheel’s caked up and has to come out for cleaning.
I wouldn’t do this one yourself. There’s line voltage in there, a gas valve sitting right above it, and multi-speed motor wiring is real easy to mix up.
When a Repair Isn’t Worth It
Her furnace was maybe twelve years old and in decent shape otherwise, so a motor was the right call. If it’d been closer to twenty, with a cracked heat exchanger or a control board that was already acting up, I’d probably have told her to save the money for a new one. When a furnace that old starts making a new noise, that’s usually when I bring it up.
Replacing one in Prescott is more of a project than people think. You generally need a mechanical permit and an inspection, and nobody wants to be waiting on that in January with the house at 50 degrees. We’re up around 5,400 feet here and it gets down into the low 20s at night pretty regularly in the winter, so I’d rather talk about it in October.
Don’t Wait on It
A squealing bearing doesn’t fix itself. They tend to give out when the furnace is working hardest, usually the coldest week of the year, when everybody’s booked. It’s good to have an ally you can call before it gets there. Give Allied Electric a call and we’ll come find the noise.
Common Questions
Furnace squeals for a few seconds when it starts then stops, do I need to worry
Not tonight, but I’d get somebody to look at it. Squealing that only lasts a few seconds at startup is usually a belt slipping or a bearing that’s dry until it warms up. It’s not gonna get better on its own.
Can I just spray wd40 on it
I’d rather you didn’t. It’ll get quiet for a week or so and then it gums up with dust. If your motor has oil ports, non-detergent motor oil is what you want. If it’s sealed there’s nothing to oil.
Is a squealing furnace dangerous
Not usually in the fire sense. The bigger risk is the motor seizing and you waking up to a cold house. If you smell anything hot or burning with the noise, shut it off at the thermostat and call somebody.
Why is it louder on really cold nights
It’s running longer. On a 20-degree night in Prescott your furnace might run fifteen, twenty minutes at a time instead of five, and a worn bearing heats up and gets noisier the longer it goes.
How much does it cost to fix a squealing furnace
Depends on what’s making the noise. A belt or a little adjustment is on the cheap end. A blower or inducer motor runs more, especially if it’s a variable-speed ECM. Whoever comes out should show you the bad part and give you a price before they start. And if it’s squealing right now, just notice when it starts. Saves me a lot of time when I get there.
