Fix Banging Furnace Ducts
LESLIE: Daniel in California is dealing with a heating issue. Tell us about the problem with the furnace.
DANIEL: Yes. I have a forced-air furnace and I’m in a single-family (inaudible at 0:29:39.8) with one level. And the furnace goes on, it reaches the temperature that we set it at and then it goes off. And then 10 minutes later, I hear this slamming like it’s a sheet-metal gate closing rapidly.
DANIEL: It’s a bang. You hear it throughout the house.
TOM: Mm-hmm. It’s called oil canning.
LESLIE: That’s the duct sort of popping, right?
TOM: It’s the ducts. What happens is as your furnace kicks on and off, the ducts fill with air and they expand and they pop. And then as the furnace goes off, the air rushes out of the ducts and then they sag and they pop again. So, it’s the sort of metal banging sound as the ducts expand and contract.
Now, somewhere in the line of ductwork, you’ve got a section that’s doing this. Normally, when contractors install ductwork, you’ll see that they put bends in it that are sort of like X-shaped or diamond-shaped. That gives that duct some rigidity and stops it from doing all that flexing. It’s like metal sheets banging as they expand and contract. It’s why it’s called oil canning – like the old-fashioned metal cans that you could sort of bend, they would make a lot of noise; before they were real soft, aluminum cans like we have today. That’s actually where the term came from.
But the fix is basically to add another piece of metal on top of the duct where it’s making the noise. You take like a small angle iron and screw it to the duct to give it some strength; some rigidity. And frankly, you could do it with a stick, too, like a 1×2; just anything to give that duct some strength. And that will stop it from making that racket.
DANIEL: Oh. I just have to locate where it’s coming from.
TOM: That’s correct. Yep. And start near the furnace; it’s usually close to the furnace.
DANIEL: Oh, that makes sense. Well, that’s great. That’s great. (chuckles) I’ll take care of that. You’re the best.
TOM: See that? Simple solution, Dan.
DANIEL: Yeah, it sounds good.
TOM: Alright. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.