Thermal Expansion While Heating - Probably Not Ductwork


Old 11-20-20, 08:53 AM
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Thermal Expansion While Heating - Probably Not Ductwork

Hello, I just moved into a new-to-me home (constructed in 1978), food framed, with a gas-fired forced air heating system.

I've only been moved in for a week but quickly noticed when hot air begins to flow through the supply ducts, I hear what sounds like the framing of the structure all over the house expanding. A little does not bother me but this occurs in multiple places throughout the entire house every time the heat comes on, often times loud enough to wake me up.

Is it possible/likely that ductwork (all in the attic) is directly contacting the framing of the structure, without insulation between, and causing it to heat up rapidly? If so, any suggestions to remedy this? If not, any suggestions on other things to check for? I can't tell if it is flexible ductwork or ridged duct work wrapped (or just covered over the top) in insulation.

I'm happy to climb up and take photos and post tonight if that would be helpful. Also happy to record video footage with audio to demonstrate. Perhaps it is the ducts themselves directly rubbing along the framing and has a small earthquake-like energy release when it overcomes static friction.

Thanks in advance for help!

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Old 11-20-20, 10:10 AM
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What you are probably hearing is the duct expanding, not the framing of your house.
Old 11-20-20, 10:13 AM
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I will say the reason I believed it to be framing and not duct work is that wind gusts have stressed the structure while heater was not running and sounds very similar to the thermal expansion sounds, both different from metallic expansion I've heard in my previous house.

Sounds like I may need to take a trip into the attic when heat is on and take a closer look/listen.
Old 11-22-20, 12:18 AM
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Sounds like you have metal ductwork: Flexible or fiberglass ducts wouldn't do that. Images would be good.
Old 11-22-20, 04:57 AM
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A little trick to help track down the source is to remove several supply grills and place your hand into the duct and hold it to the surface of the duct.
It needs a bit of patience but if you turn up the heat and feel for a vibration in the metal that may accompany the sound it may help pinpoint the source.
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