On Jan 16, 9:19*pm, TimR wrote:
On Jan 16, 1:59*pm, DerbyDad03 wrote:





On Jan 14, 8:28*pm, Peetie Wheatstraw
wrote:

I belong to a little brick bungalow in the midwest US built in 1954. Original
forced-air (galvanized ductwork) heating, 2-yr-old Heil 80% furnace.

Lying in bed, very quiet, furnace begins heat cycle. About 15 seconds after
the burners fire, I hear a big POP. Very consistently. Every night.

I know that the furnace heat makes the sheet metal expand, and a certain
amount of noise (creaks, squeaks, etc) is to be expected, but this one sounds
too loud.

Walked the length of the ductwork, tapped each joint with a mallet, inspected
everything. No apparent problem.

Still I get the big POP.

Anything with 50-year-old galvanized ductwork that I should be looking for?

* Thx,
* Peetie

If it's happening "Very consistently. Every night" then grab a
sleeping bag and sleep next to the furnace one night, halfway to the
bedroom the next, etc.

Seems like within a few days, you know exactly where the noise
originates and then be able determine the actual cause.- Hide quoted text -

- Show quoted text -

You *could* have a damper in the duct that opens in closed. *Common in
commercial buildings, I've never seen one in residential but that
doesn't mean there isn't one.

But if I had to guess, I'd say the most likely cause is something
called snap-through, pop-through, a couple of other terms. *A slightly
convex surface can be stable in two configurations, and under air
pressure (more likely) or temperature (less likely) changes can pop
through to the other. *You can probably play with a beverage can and
reproduce it.

If that's what it is, it is harmless.- Hide quoted text -



I think it's also called "oil canning" and is not anything to worry
about, but can be annoying.
Mark