How can I stop our duct work "pinging" at night?

Question

I'm in Canada, and our home is a bit older, ~20 years, and the duct work seems to be making a rather loud "pinging" noise at night. I assume this is due to colder weather in general, and the hot air from the furnace heating the duct work up.

The noise, however, does bother my wife, and I'm looking for some advice on how to resolve this. (Currently earplugs are an option we use at times :) ) As I'm a heavier sleeper, it doesn't really bother me though I have heard it. It's not audible during day; there is too much other noise masking it, so I hope that helps understand how "loud" it is.

I never really noticed this in previous houses, so I'm curious as to how "normal" this is, and if there are any "simple" methods for fixing the issue? (I don't really want to call in somebody to replace all the ductwork.)

Is there something simple I can do to reduce this pinging? Is there some simpler task I can hire somebody to do to identify the "problem area" and fix/repair it?

Answer 1

Sometimes ductwork under pressure and heat can experience a sudden deformation commonly referred to as oil-canning. This is where large rectangular pieces of box ducts have stiffening ribs formed into them to prevent deflection under pressure.

If a particular panel is installed in just the right (or wrong) way, it can temporarily flex when it warms up. It's usually coincident with a loud ping as described. It generally repeats when the heating cycle ends, it cools down and it returns to its original shape. If you can find the specific duct portion that's doing it, you can stop it by gluing a damping plate (piece of plywood or steel) to the outside face of the offending duct panel.

Answer 2

I'm dealing with the same problem in our "new" (1992 vintage) home. Long duct runs expand and contract with conditioning cycles. In places where the duct is held tightly against the home's framing or other objects, sudden slipping results in pops or squeaks.

Solutions generally involve one or more of the following:

• securing the duct more effectively at the contact point so it can't move against the lumber
• loosening the attachments so it can move with less noise
• lubricating the contact points with something like wax to allow freer sliding

To make location and diagnosis easier, allow the home to cool for a bit by turning off the furnace, then run it and listen. It may help to have several people on hand to more quickly locate the problem, as it may stop making noise once things are up to operating temperature.

Answer 3

There are all kinds of special sounds absorbers for ducts. They are not the lightweight acoustic egg crate shaped foam, but very heavy and somewhat flexible, but not springy. They lower the Q Factor of the sheet metal.

McMaster sells them: http://www.mcmaster.com/#sound-control-duct-silencers/=zyyku7

The same page also has sound control coatings that work by the same principle, you can find them in any car store for dampening cars.

Answer 4

If you have spots that "oil can" in and out. You can get some light gauge angle metal. L shaped lengths. Trim them to the width of the duct. Pre drill a few holes in them. Attach with sheet metal screws across the spot that is flexing in and out. My cold air return was doing this. One angle on each side of the long vertical run to the furnace solved the problem. My first temporary fix was a couple pieces of 2x4 held tight with a cargo strap. Keeping the sheet metal bowed inward.

Answer 5

We had a kind of rubber inserted between the brackets and ducts which helped a lot.