Downstairs neighbors hear loud banging when we're running hot water

May 24, 2023 11:05 AM

As the title says! We are in an upstairs condo and our downstairs neighbor has very sweetly and kindly explained that they've been hearing loud noise at all hours of the day. Through some investigation we found out it happens whenever we run hot water - from any sink, shower, washing machine, etc. We're going to make an appointment with a plumber, but any thoughts on what may be happening in the meantime?

My husband and I don't hear anything upstairs, aside from the usual expansion in the hot water heater (which doesn't sound unusual and seems fairly quiet). We also haven't done an in depth test with the neighbor to figure out if it's during the heater refilling or pushing water through, initially.

All we know for sure right now is is they're hearing loud sounds throughout the entire condo (two bedrooms, living room, etc.) and it seems to be tied to us using hot water only. We own our unit but I believe they rent, and they have a baby which I feel awful about waking when this happens.

I'd love some hypothesizing on potential issues before the plumber takes a look at both our units!

posted by It Was Capitalism All Along to Home & Garden (12 answers total)

Could be water hammer (noise when a faucet is abruptly closed) or pipe expansion. (Metal gets larger as it warms up, can make popping noises etc as the pipe hangers shift or bind)
posted by Larry David Syndrome at 11:09 AM on May 24, 2023 [9 favorites]

Best answer: Can you describe the noise? I started thinking like Larry David Syndrome that it's a hot pipe expanding/stressing against a support, which makes a clicking noise.

It's also possible that the water heater is knocking/popping, which can be fixed by flushing the sediment out of the unit. That would be a different kind of sound.
posted by JoeZydeco at 11:34 AM on May 24, 2023 [1 favorite]

My bet is on water hammer. My house does this too. It doesn't bang if I turn the faucet on/off slowly instead of quickly. Start and stop with a trickle and see if that doesn't solve it at least temporarily.
posted by SaltySalticid at 11:59 AM on May 24, 2023 [3 favorites]

I’m also guessing it’s a water hammer issue. This can be very annoying to fix.
posted by samthemander at 12:18 PM on May 24, 2023

water hammer can also happen when a toilet is flushed and the valve cuts off flow. The only way I know to regulate that particular issue is to slow down the water coming in from the fill line. If others have solutions, please offer them
posted by TimHare at 12:28 PM on May 24, 2023

Another water hammer.... happened to me with sprinklers.
posted by answergrape at 1:20 PM on May 24, 2023

I've seen sometimes where renovations were conducted in a home and the contractors for whatever reason find this odd sort of loop-the-loop configuration in one of the water lines and it's taking up valuable space and it doesn't really appear to serve any function so they cut it out and replace it with a straight pipe instead. Then later on the owners can't seem to figure out why their water pipes make this banging noise every time they use the hot water. Turns out that weird conflabulation of copper pipe in their walls was something called an expansion loop, and it's purpose it to prevent exactly this kind of thing from happening. Maybe you're in a similar situation here?
posted by some loser at 2:02 PM on May 24, 2023

Water hammer seems likely but I would think that OP would hear it too. It’s loud and you can often even feel the vibrations.
posted by SoberHighland at 2:54 PM on May 24, 2023

Water hammer arrestors can be installed in a line. It's also possible you have PEX pipe for your hot water lines that's inadequately secured and you need to open walls/ceilings and strap it down every 18" or so.
posted by cnidaria at 2:55 PM on May 24, 2023 [2 favorites]

Best answer: I break the consensus on water hammer.

We have had banging when using hot water. The noise comes from the hot water heater. On the casual advice from someone else's plumber, we drained the water heater. It disgorged a bunch of white sand-like material. The banging was not eliminated, but it became weaker. We are going to drain it again pretty soon in hope of additional improvement.
posted by SemiSalt at 3:12 PM on May 24, 2023 [1 favorite]

Response by poster: Thank you so much folks! They described the noise as something that sounds like construction, and right now my bet is on sediment in the tank. We hear some ticking and soft popping when we use hot water, but nothing as extreme as construction banging. However I wouldn't be surprised if there's shoddy plumbing or other actual construction between the units that cause sound to travel strangely far!
posted by It Was Capitalism All Along at 7:44 PM on May 24, 2023

Response by poster: Quick update to this, it was the sediment after all. We got what seemed like a decent amount out with the first flush, but didn't notice any difference in the sound. Scratched our heads and tried again the next day, got a waaay smaller amount but it seemed to make a surprising difference after. Then came a final flush to get what was hopefully the last bits, and our heater is blissfully noise free.

I'm surprised by how long the process needed to be, none of the flushes were very effective with the tank fairly full. It has to be mostly drained each time before a new flow of water dislodged enough gunk. I was under the impression that draining it over and over wasn't necessary, but I'm hoping that'll be the case moving forward, at the very least. Our hard water is the worst.

Case closed!
posted by It Was Capitalism All Along at 8:04 PM on June 2, 2023 [1 favorite]