Banging pipes & water hammer noise diagnosis, cure:
Water hammer noises in plumbing is also called hydrostatic shock. Our page top photo shows a water hammer noise suppression device produced by Oatey and available at building suppliers.
This particular water hammer noise suppressor is interesting because it's designed to be added to a hose bib or washing machine hose connection by a homeowner, avoiding having to cut and solder pipes.
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The articles at this website will answer most questions about plumbing noise associated with water hammer or water surge, including the diagnosis and cure of water hammer noises as well as many other building plumbing system inspection or defect topics.
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Image at left provided courtesy of Carson Dunlop Associates, a Toronto home inspection and education company.
We divide water hammer or banging pipe noises in buildings into two categories:
Definition & Actual Cause of "Water Hammer" Noise
Water hammer (or hydrostatic shock) is a noisy pipe problem that occurs when valves are shut off quickly. You may hear banging water pipes, or clanging, rattling, or rumbling noises in the water piping when a plumbing fixture, sink, or clothes washer turns off. Here is a more scholarly definition of water hammer that is rather clear:
When Increasing Water Flow Rate or Velocity or GPM, Watch out for Both Water Hammer & Water Scrubbing Damage
As we discussed over at CLOGGED SUPPLY PIPES, REPAIR,
High Velocity Water Flow Rates Can Cause Water Hammer
Think of water screaming along at 100 mph: it's doing pretty nicely until it hits a curve (maybe a pipe elbow) or a wall (a valve that has suddenly shut). Then SLAM!
Watch out: as we discuss at WATER HAMMER NOISE DIAGNOSE & CURE, if the velocity of water in your piping system is too fast, when faucets or other controls STOP that water flow you may hear a horrible hammering or banging in the piping system. Water hammer is more than a horrible noise, it can damage equipment, cause potentially dangerous leaks at tempreature/pressure relief valves, and may even cause a divorce.
High Velocity Water Flow Rates Can Cause Scrubbing Damage & Water Piping Leaks
A second problem with very high water velocity rates through building piping is scrubbing or wearing away of the pipe interior: a problem that occurs at very high water speeds (measured in feet per second) in piping systems.
Generally the maximum safe water velocity or speed in residential water piping systems is 7 feet per second, and for 2-inch or llarger pipes you should not exceed 5 feet per second. Some piping types such as PEX (CTS SDR-9) at smaller diameters such should have flow rates limited still further. 3/8" PEX should be limited to 3 gpm at 10 ft3/s. [CTS = copper tube size and SDR = standard dimension ration of pipe wall thickness to pipe diameter].
Scrubbing is more of a worry in metal piping than in the smoother (less friction) plastic piping systems. Scrubbing and corrosion are common sources of pinhole leaks in water supply piping.
Note: to convert between cubic feet per second of water flow into gallons per minute we need to know just two magic numbers:
1 minute = 60 seconds
1 cubic foot = 7.5 U.S. Gallons
A flow rate of one cubic foot per second, then will give us 7.5 gallons per second or in a minute, 60 x 7.5 = 450 gallons per minute. That's a lot of wateer.
How Water Hammer Can Damage Water Pipe or Pipe Connections and Result in Leakage
In more layman-like terms, water hammer works like this: water passing through a pipe has momentum or velocity. When the valve is shut quickly, the momentum of the water carries it into the valve with considerable force. Since water is essentially incompressible, a large pressure is built up against the valve, and there is low pressure upstream in the pipe. The high-pressure water wants to flow to the low-pressure area.
This happens so quickly that a small vacuum is created against the valve as the water moves away from it. This can result in cavitation as the water is pulled back against the valve a second time. This continues back and forth in slowly diminishing shock waves. Pressures up to 600 psi (some sources say 1000 psi) can result from water traveling up to 3,000 miles per hour, for very short periods.
Water hammer can result in loud noises in supply plumbing pipes. Water hammer only occurs as valves are closed. If a valve is closed slowly, and the noise does not occur, one can be sure that water hammer is the problem.
Water hammer is common with quick-closing electrically operated valves on appliances such as washing machines and dishwashers. Air chambers can be installed to control water hammer, as Carson Dunlop's illustration (above) demonstrates.
Causes of Water Hammer / Hydrostatic Shock Include
Diagnostic Tips for Determining that Banging or Rattling Pipe Noise is Water Hammer
If you hear a rattling, banging, or clanging that seems to come from building pipes AND if the noise stops when no water is being run in the building most likely you're hearing water hammer.
Try this: when you hear the water hammer noise, turn water on to increase the flow rate at one or more fixtures, OR turn the water flow rate off slightly to slow the water flow. Often changing the water velocity in the piping system will cause the water hammer to stop - a diagnostic clue.
If you hear banging pipes when no water is running (check to make certain that all water is off, including filling toilets, outdoor sprinklers etc.) then the banging noise may be a heating pipe problem that we discuss at BANGING HEATING PIPES RADIATORS
Cures for Water Hammer or Air Hammer - Hydrostatic Shock Noises in buildings
Again quoting our admired hydraulics expert Brian Boman,
Also see SOUND CONTROL for PLUMBING for an extensive list of causes and cures of building plumbing noises.
Also see NOISES COMING FROM WATER HEATER for the diagnosis and cure of clanking or thumping noises that may be coming from your water heater or heating boiler.
- Adapted with permission from The Home Reference Book
If it sounds as if someone is down in your BASEMENT or cellar banging on the heating pipes with a hammer, and particularly if your buildijng is heated with steam radiators, the noise you hear may be due to water hammer in the steam piping system.
In both one-pipe and two-pipe steam heat systems steam rises into the building's heating radiators, forcing air out of the radiator's steam vent , then making the radiator hot. Inside the hot radiator steam condenses back to water as heat is radiated (by the "radiator") into the room.
This steam condensate must drain back into the steam boiler where it is subsequently re-heated to steam to continue the heating cycle. But if the condensate is having trouble returning to the steam boiler your heating pipes may become waterlogged. This happens because when the steam boiler water level drops and is not replenished by returning condensate, the automatic water feeder will just send more water into the boiler.
Condensate accumulating in the steam piping (when it should be returning to the boiler) not only water-logs the system, it also means that cooler condensate (water) comes into contact with hotter rising steam in the piping. This contact can cause rapid expansion/contraction in the heating pipes and produces the loud "pipe banging" noise we are discussing.
Your heating service technician should be someone familiar with steam heating systems and the proper layout and function of condensate return lines in your home. The tech will look for a problem that is blocking condensate return to the heating boiler, such as a clogged strainer in the system piping, a steam trap clogged with rust, minerals, or sediment, or a similar problem.
A separate problem: failure of individual steam radiators to get hot, could also be due to blocked condensate return. If a radiator's steam vent is not working, or if a one-pipe steam system's radiator has settled so that it is no longer properly tipped to send condensate back into the steam pipe (and back to the boiler), that radiator will stop working. But individual radiator troubles do not usually explain banging heating pipes.
Watch out: If your heating boiler does not have an automatic water feeder and you've been putting makeup water into the boiler manually, a blocked condensate line and low water in the boiler will eventually lead to total loss of heat when the low water cutoff switch , a key boiler safety device, simply shuts down the boiler.
Other causes of heating system noises are discussed
Where to Buy Water Hammer Arrestors - water hammer suppression products
Reader Reports Saga of Searching for an End to Water Hammer at the Water Heater (Cylinder, Geyser)
9/12/2014 Bruce Reid said:
I have a brand new water heater which i rent from my utility company. Ever since they installed it, i've had water hammer noises on all fixtures in my house be they hot or cold. At first I thought the noise was just a loose pipe, so I called the utility to come and restrap the pipes tightly to the joists like they were before. The new heater is in a slightly different position than the previous one so they had to pull the pipes down a few inches.
They also used Shark Bite connectors this time around. That's the only difference I can see. So now I have this hammer noise on any faucet or toilet in the house, and even the outside garden hose. The noise is loudest RIGHT NEXT to the water heater. If i turn off the water supply to the water heater all the noises go away. so that means it's the the heater's fault, right? My questions are these:
1) Why would a new water heater cause WH noises even on cold lines?
2) Should the utility have to pay for this? 3) The instructions for the arresters are to put them near the fixture that is causing the noise. Well ALL fixtures can trigger it, but i'm pretty sure I'd blame the heater. Would it be wise to install an arrestor right at the cold water intake of the water heater?
Your diagnosis is important and helpful but maybe not the last word. The water hammer may be due to the velocity of water entering or leaving the heater - not the fault of the heater itself.
Try slightly closing the cold inlet to the heater to see if that fixes the trouble. If it doesn't you'll want to install one or more water hammer prevention devices ahead of or after that appliance.
9/13/14 Bruce Reid said:
Hi Dan, thanks for the tip.
I turned it halfway off this morning and am still hearing the banging, and i'm not sure if it's my imagination or not, but there seems to be a related "echo bang" now. Instead of one loud bang, i hear 2 small ones.
I'm going to experiment with this a bit more at different levels of closure of the cold water inlet.
Still. Old water heater- no noise. New water heater - lots of noise. One can only assume that it's the water heater's fault right? As i was saying, the only difference in my house is one new water heater, two pipes (in and out) that were slightly stretched to reach the heater and the use of shark bite connectors to the WH instead of soldering the pipes
On track to debug, one can but ask, so what changed: just the heater, or perhaps also nearby piping; possibly the new heater replaced one whose inlet was partly clogged, slowing water flow. Or a valve was changed, or pipe routing. Ultimately understanding water hammer (velocity and sudden stoppage) leads to either modifying flow rate or installing anti-hammer devivces.
thanks again for your continuing advice. This is really useful.
Water Hammer Test conditions:
1) Turn water inlet to the WH completely open. (this is the normal configuration). Fill the water bucket in steady 2-3 second bursts from the hose. The result is the expected Bang followed by 1-2 smaller echoing bangs about a second later.
2) Turn water inlet to the WH completely CLOSED. Fill the water bucket in steady 2-3 second bursts from the hose. The result is SILENCE. Not a sound
3) Turn water inlet to the WH to half open. Fill the water bucket in steady 2-3 second bursts from the hose. The result is the expected Bang followed by 1-2 smaller echoing bangs about a second later.
4) Turn water inlet to the WH to 1/10th of a turn open (practically closed). Fill the water bucket in steady 2-3 second bursts from the hose. The result is the expected Bang followed by 1-2 smaller echoing bangs about a second later.
My intent here was to find that sweet spot in the water inlet valve that would reduce the sound to zero. Apparently that doesn't exist. Any opening means noise.
So there you have it. In a cold water only test, we get bangs from the area around the WH on any situation where the water inlet is open. Even just a crack.
On hot water tests, using another fixture, for example, the kitchen sink, with hot water tap turned on the bang is a bit bigger.
So if hammer arresters are the solution, where would you suggest putting them. on the cold water supply line to the WH? Note that's a bigger diameter pipe than the rest as you'd expect.
(I've run out of available text space here so I'll put more info in a later post.) thanks again!
Reply: where to install the water shock / water hammer arrestor
Nice going Bruce.
I confess that I've tried fixing water hammer by adjusting building water pressure or by controlling flow rate into an appliance like a water heater with only mixed success.
Have you tried buying a water hammer arrestor device and installing it on the water supply line near the heater? I'll summarize again the standard things to try when stopping water shock or water hammer noise in a building.
How to Choose & Install a Water Hammer Arrestor
Summary of steps to stop water shock or water hammer in a building
Continue reading at WATER HEATER NOISE DIAGNOSIS, CURE or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Some of the FAQs discussed below are adapted from information provided by the Watts Regulator Company in a 1973 publication.
Question: when I flush the toilet there is a loud sound like a jackhammer
(July 3, 2014) Krystyl Cruz said:
When I flush the toilet, a few seconds later (when the water is refilling) a loud sound like a jack hammer comes from the wall behind the toilet. Sometimes if I turn the faucet on in the sink the banging will stop, but if I turn the faucet back off the banging starts again until the toilet stops running.
You are almost certainly describing a water hammer problem. I've found just the symptoms you describe including that opening a faucet, because it changes the flow rate and pressure in the piping, can move the flow rate off of that speed that is causing the horrible banging sound.
Question: does water hammer in my plumbing system cause damage?
What effects can water hammer have on my house plumbing system? Other than making noise, does it actually hurt anything?
Water hammer causes a sudden "banging" of water supply piping that creates movement and stresses in the system, not just annoying noise.
Water hammer can cause loosening of water supply piping connections, leading to plumbing leaks and related damage
Watch out: Water hammer shocks to the water supply system are more serious at higher operating pressures. On hot water heaters the TP valve is usually set 20 to 30 psi above the anticipated maximum system water pressure. This is high enough that the relief valve won't leak or spill when water hammer occurs in thte system. But at higher water pressures, say 70 psi to 90 psi, the relief valve may be damaged or leak when water hammer occurs.
At our article on WATER PRESSURE REDUCER / REGULATOR you 'll see that we recommend against operating a home at pressures above 70 psi because of the increased risk of plumbing system or plumbing fixture leaks.  paraphrased
Question: can I record water hammer noise? Loud banging that isn't water hammering?
(Oct 27, 2011) Ian Anderson said:
Hello, is there sound recording equipment to prove water hammer noise from neighbours flat?
(Jan 15, 2012) Anonymous said:
Mike I have a 75 gallom power vent gas hwh the home is well water ther is a check valve on the cold water side of the hwh there is also a expanchion tank n both are between the ball valve and hwh i am getting alot of load banging on both the hot and cold side when water is running and it isnt water hammering because i put air aresters on system its happening when both cold and hot are running I was wondering if it was the check valve causeing the banging sound ?
Ian, you can use any recording equipment, even a sound recorder on a cell phone to record the sounds you describe. I've done that with great success. If you are using a cell phone hold it against a noisy wall or ceiling for strongest sound transmission into the device.
Anon: Putting air arresters onto the system may not have been enough to cure the water hammer if they were too small in capacity.
Question: loud hammering noise wakes me up
(June 21, 2012) jt said:
I am hearing loud hammerins noises, loud enough to wake me up, in the middle of the night. It sounds like the tap is being turned off and on but this is not the case.
JT, if the loud hammering noises are in the water supply piping, it seems most likely that someone is turning water on and off, or a well pump is turning on and off on its own - if you have a well pump try checking out causes of the well pump "turning on by itself".
Securing loose piping and installing a water hammer control device (described in the article above can also help stop the problem.
Question: various banging, moaning, clanging plumbing noise complaints
(Sept 2, 2012) Tom said:
The noise is not as much about banging but a loud moan in the hot water line between the washing machine and the Master bath tub supply, although if you flush the toilet the noise stops until the tank is filled. Have tried everything from turning off the water and draining all the lines and refilling each line in different sequences, nothing works?
(Jan 4, 2013) Ted L. said:
Thermal Expansion: When water is heated in the Water Heater it causes water to expand thus an increase in water pressure. A Code requirement and solution is to install an Expansion tank on the cold water supply line ahead of the Water Heater. The rubber gland will absorb the expanded water and release it when a tap is opened. Expansion problems prevail when no water is being used and the tank is heating.
(Jan 19, 2013) Gary S. said:
I live in a 37 unit appartment and at nightime I can hear a low pounding noise in the distant Would this noise affect the heat temp in my unit. I have hydronic heating.
(Feb 25, 2013) Ykip said:
I experience a severe water hammer when turning on and off the bathtub spout. How can I fix the water hammer arrestor on it? It seems impossible. The water pressure to the house is normal and about 70psi. I appreciate anyone to help me. Thanks,
Question: Rumbing pipes under the toilet
(Mar 5, 2014) Help! said:
My house pipes seem to rumble under the toilet. The toilet is upstairs
This rumbling doesn't sound like water hammer. Water hammer is a percussive "BANG!" that or maybe "BANG BANG bang clank" short duration clamor that occurs when water is running (fast and at high pressure and flow rate) and then is suddenly shut off.
If it's not a coincidence, sitting on the toilet or walking into the bathroom wouldn't be expected to impact a water hammer problem so I suspect we're looking for something else.
Let's start by trying to isolate systems to find out which system is responsible. I suspect we're looking at something related to heating, not water supply, or a water heater.
Water heaters that have formed a scale deposit on the heater bottom will often make an ongoing rumbling popping sort of sound * when the heater is operating * that is, when it's heat source is on.
So when you hear the noise let's notice what systems are running and which are off.
Or you could turn off the water heater for say half a day and see if the noise abates.
Search InspectApedia for "Water Heater Scale" to read more about this hypothesis.
Keep us posted and we'll pursue it.
Question: water pressure booster pump noise
(Mar 9, 2014) Anonymous said:
water pressure booster pump noise going through my water pipes what can I do?
If th problem is not a banging when water is turne off in the building then I guess you refer to the transmission of noise from the pump motor. You'll want to look at sound-isolating fixtures to isolate the vibrating piping from the building structure. Regular pipe hangers won't do it.
(Apr 3, 2014) ron said:
at our cottage the water system was fine. its a submerable pump with an air bleeder valve just before the electrical switch. its 25 yrs old. however it seams that when we replaced the tap in the shower the pipes started to shake and water spurts out. This happens after we have used the water system for a bit then it keeps banging/shaking/spurting. also when filling the toilet. thanks
It's not a complete surprise; sometimes when we simply change the water flow rate we change the vibration behaviour of the system.
It might be diagnostic to open a tap when you hear the banging water hammer noise. Openign a tap elsewhere changes the pressure and flow in the system.
I'd also double check that nothing has changed on the water supply end.
Let me know what you find.
Question: banging noise in pipes at night, 3-5 seconds apart, 7-8 bangs
(Apr 3, 2014) Dave said:
My question is this. At night i am hearing a banging in the pipes every 3-5 seconds of approximately 7-8 bangs. They can be felt when touching the pipes from the laundry room. They are not overly loud. The seem to go away for a brief time when I run the water at the lowest faucet in the house. Any ideas?
You're probably describing water hammer as we discuss it above.
Question: trouble tracking down water hammer noise
(Apr 19, 2014) Lynn Pepe said:
For the past 5 days, we hear what sounds similar to water hammer, can not pinpoint where it is coming from. Tbis happens any time of day or night, does not seem to be related to turning water on or off. We have tried shutting down the main and running the water out several times. We have had the water company to check. what can this be???
Lynn, I would be just shooting in the dark to guess very specifically, but surely if you hear the sound when water into the building is shut off completely it's not a water supply system problem. At that point I'd be looking at hot water heating, steam heating piping, and if those are ruled out, I'd be looking for other sources of mechanical movement.
Question: will the Temperature & Pressure relief valve protect the hot water tank against water hammer damage?
Will the T&P valve protect the tank against breaking from excessive water hammer? - Watts
An "excessive" water hammer is an abnormal but momentary condition that causes a very brief surge in water system pressure. The pressure-relief component of a temperature and pressure relief valve can only discharge a verly limited amount of the surged pressure during the moment of shock of the water hammer event, possibly none.
If water hammer is causing frequent opening of the temperature and pressure relief valve there may also be a risk that the frequent passage of hot water through the valve deposits scale that eventually accumulates to a level at which it prevents safe reliable operation of the valve in an emergency.
And the fact that temperatures inside the hot water storage tank are elevated above cold water temperatures makes no difference - with the exception of the warning we issue next.
Watch out: if the hot water tank is in an abnormal overheated condition, that is water in the tank has become superheated above its atmospheric boiling point water hammer could actually lead to a water heater tank explosion. According to Watts Regulator Company, "Water hammer conditions are believed to be a partial factor in starting off an explosion of overheated tanks besides "pressure heat rupture".  paraphrased
Question: septic pump check valve noise
5/29/14 Naaj said:
Water-hammering noise from check valve in septic sump pump…solution?
Check that you don't have multiple check valves installed on the same piping system. If there is only one then you're ok on that score and you'll want to install an anti-water hammer noise product such as those discussed above.
Question: ball cock in the water tank in loft causeing water hammer
(Oct 18, 2014) mr conner said:
can it be the ball cock in the water tank in loft causeing water hammer
No, not directly but possibly indirectly:
Water hammer is an effect of the velocity of movement in water pipes along with pipe dimensions and layout, combined with a sudden STOP! of water flow. Any valve can "cause" the effect to be heard. Some plumbers install slow closing valves to reduce the problem but you'll read other solutions in the article above.
Question: banging pipe issues
(Nov 3, 2014) Hope said:
We recently had issues with banging pipes in our home. A plumber recently came out and replaced the water pressure regulator along with adding an expansion tank to our water heater but now after a month or so the noise is back and isn't happening when the water is running like it was before but when the water softner is running. Please help...what could the problem be now?
I'd like to help but with not a shred of information about your home, piping, water supply, pressure, valves, usage, etc. my best advice remains in the article above. If any part of that is unclear please just ask.
Question: banging pipes and water softeners
(Nov 18, 2014) A Kang said:
At my home (Cypress Texas), we hear water hammer noise at the end of water softner regeneration cycle. There was no water hammer prior to installation of water softner. I brought in the water softner installer and could not figure out why and told may be water pressure is high when the regeneration cycle occurs. He changed regeneration cycle time from night to afternoon and we still have water hammer.
The regeneration cycle is after 10 days and lasts for 1 hr 45 minutes. Did water softner not installed properly? The house was built in late 2010 (by village builders a subsidiary of Lennar Homes). We had water water softner installed in 9/2011. We purchased this new home and moved in April 2011. I called in a plumber and he was not much help. I am considering to contact the plumbing company (New Tex) who did the original plumbing in the home. May be they can figure out and fix this problem. Any guidance you have. Thanks
Ask about installing either an appropriate water hammer control device (described in the article above) or a slow-closing control valve on the supply to the water softener.
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