Clicking noise in exhaust flue pipe

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Burgher

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Hi. We just moved into a newly built house in Canonsburg PA (south of Pittsburgh). Our Bradford White powered vent water heater is vented through a 3” PVC pipe in two 20’ sections to the outside vent. There are 3 elbows on the way out. About 3 feet from the point where the two horizontal pipes join (23 ‘ from the last elbow) there is a clicking noise that we hear whenever the exhaust fan is running. It’s not loud but it reverberates through the floor into our bedroom and drives us crazy. The clicks vary in frequency from one every 15 seconds or so to maybe up to a minute. My wife thinks it’s a dripping sound but to me it’s a clicking or a tapping sound.

Any ideas as to what could be causing this or how to eliminate this noise?
 

Reach4

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It could be thermal expansion, and the PVC pipe not slipping smoothly through holes as it expands.
 

Jadnashua

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Reach is almost certainly correct. PVC expands and contracts quite a bit. Say the temperature rises 40-degrees, over 25' when exhausting, the pipe will become nearly 3/8" longer. The actual rate in inches is 28x10^-6/degree F. It not only gets longer, it gets larger in diameter, but since that is over a fairly short distance, the diameter doesn't change much.
 

Burgher

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Reach is almost certainly correct. PVC expands and contracts quite a bit. Say the temperature rises 40-degrees, over 25' when exhausting, the pipe will become nearly 3/8" longer. The actual rate in inches is 28x10^-6/degree F. It not only gets longer, it gets larger in diameter, but since that is over a fairly short distance, the diameter doesn't change much.
 

Burgher

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Interesting. Would the clicking be coming from the point where the pipes are joined or from rubbing against the wooden joists? And what would the remedy be?
 

Jadnashua

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It's usually from a tight hole or a rub against something where it doesn't have enough clearance.

What usually is happening is that there's some friction, as things expand (and contract), the friction holds the pipe in position until it can't, then it jumps a little making a sound you can hear...then repeats.
 

Reach4

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If the pipe is a little off center in the holes a few places, I wonder how the little plastic clips they use to close bread bags would work instead of cardboard. They seem like they might be slicker. I think you would want to insert a tag or two on the tight side.
220px-Bread_clips.jpg
 

Dj2

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Reach4,
This picture of bread clips represents a lot of breads...
 
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