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Noisy Plumbing and How to Prevent It

Tech Note #111800.1
Last Update 06.30.12


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Water hammer is a destructive force that can damage residential or commercial plumbing systems. Not only is "noisy plumbing" an annoyance, but shock forces due to water hammer can rupture copper supply lines or cause leaking at joints. This comprehensive Builders Websource® Tech Note explores the causes and cures of water hammer and other plumbing noises, helping homeowners, designers, contractors, and plumbers to avoid the problem during the design phase or resolve an existing serious condition.

Table of Contents

Introduction - What is Water Hammer?

Water hammer is a pressure shock wave induced in plumbing supply systems whenever there is a sudden change in the steady state condition of a non-compressible liquid such as water. Pumps, valves, faucets, toilets, and fast solenoid-activated valves (such as commonly found in washing machines and dishwashers) are all examples of devices that can induce water hammer within a typical plumbing system. Water hammer can result in noisy, banging sounds as pipes rattle and expand to absorb the pressure wave. Shock waves in typical water pipes travel at up to 4500 feet/second and can exert tremendous instantaneous pressures, sometimes reaching 150 to over 1,000 PSI. If left unchecked, water hammer can damage pipes, valves and eventually weaken joints. However, the lack of noise does not mean that water hammer is not present.

Several factors exacerbate water hammer and are generally traceable to inadequate system design and installation.  These include:

  • Improperly sized supply lines for given peak water flow velocity;
  • Excessive system water pressure and lack of pressure-reducing apparatus;
  • Inadequate strapping or securing of plumbing to structure;
  • Excessively long straight runs with no bends;
  • Lack of expansion tank or other dampening system, such as water hammer arresters;

Newton's law states that for "every action there is an equal and opposite reaction." If water is flowing into a washing machine then is suddenly shut off, the kinetic energy of the flowing water reverses direction and must be dissipated during the transition to a steady state. This energy is initially reflected back through the plumbing system in a direction opposite to the original flow, creating an oscillating shock wave. Depending on the extent of the shock wave, a loud banging or rattling sound can be heard as pipes expand and move as the shock wave dissipates.

If there were no friction losses and if the pipes had no expansiveness, the shock wave would continue indefinitely. However, as water flows through the pipes, friction due to internal pipe surface irregularities helps to slow the water, resulting in energy that is converted to heat. In addition, virtually all pipes -- including drawn copper tubing -- have some measure of elasticity. As the plumbing system encounters a sudden pressure shock wave, the pipes expand slightly to absorb the shock. Pressures in excess of several thousand PSI are possible during this brief instant, which is why water hammer can burst pipes and joints unexpectedly.

Failure to properly address water hammer can yield the following dangers, according to the Plumbing and Drainage Institute:

  • Ruptured piping
  • Leaking connections
  • Weakened connections
  • Pipe vibration and noise
  • Damaged valves
  • Damaged check valves
  • Damaged water meters
  • Damaged pressure regulators and gauges
  • Damaged recording apparatus
  • Loosened pipe hangers and supports
  • Ruptured tanks and water heaters
  • Premature failure of other devices

Clearly, repairing any of these conditions "after the fact" is more expensive and inconvenient than designing a system right from the start.

Traditional Solution to Water Hammer

Traditionally, the solution to water hammer has been to install pipe risers inside the wall at each faucet or valve junction. Sometimes these risers would be as high as 24" or more, depending on the pipe diameter. In theory, the risers would trap air as the plumbing system is first activated. The column of air acts as a natural damper, compressing as it absorbs residual shock waves from a sudden change in the supply flow.

Many, if not most older homes today have such systems and some plumbers continue to install air risers because "that's the way they've always done it." However, what is not readily understood is that these risers eventually fail due to water logging. Over time, the trapped air in the risers dissolves into the water supply itself and the water level gradually rises until the air chamber is completely void of air at all. For this reason, some people who have never experienced the sound of water hammer may suddenly start complaining of "strange noises inside the walls."

The only real solution is to completely drain the home's water supply system at the lowest point and gradually re-pressurize it. However, this solution is temporary at best, since the air chambers will eventually become waterlogged once again, thereby eliminating their effectiveness.

What's more, further studies have also found possible health problems associated with air risers, such as an accumulation of rancid water, bacteria, minerals, and other muck that festers in the dark, dead-end chambers. If left unchecked and untreated, this could eventually contaminate the entire household water supply causing unexplained illness.

Therefore, modern practice and, indeed, many plumbing codes, now prohibit air chambers in new construction. In any case, if you are remodeling or building a new home, DO NOT use air chambers to mitigate water hammer problems. Rather, design the system right from the start and you'll never have to worry about it again. A combination of proper pipe sizing and water hammer arresters are all that's necessary in most situations.

Water Hammer Prevention by Design

If air chambers, then, are not an approved method of dampening the impact of water hammer, what is the correct method? First, let's consider new construction where there is no existing legacy plumbing.

In the case of a new home, there is total flexibility in sizing the water supply lines properly. Empirical studies conclude that water hammer is greatly mitigated when water velocity is kept below 5 feet/second within the pipe. This is a conservative number. And while CPVC plumbing is increasingly common (and is somewhat more forgiving at higher velocities due to its increased expansiveness), copper plumbing is still the mainstay of most commercial and residential plumbing systems today and is the focus of this technical note.

To assist contractors and plumbers in sizing the water supply line diameter at each branch of a plumbing supply system, Builders Websource has constructed several tables comparing Type K, L and M copper tubing. While type K is rarely used in residential construction, type L and M are more typical. Type K copper, denoted by its green labeling, has the thickest wall of all three types, whereas type M (denoted by red labeling) is the thinnest. Since the outer diameter for all three types is fixed, type M actually provides slightly greater internal cross section for a given pipe size due to its thinner wall size. While this can help to reduce water hammer by a small fraction, the thinner wall size is more susceptible to bursting and pin hole leaks over time. Type L copper is the best compromise for price/value and is a proven all-around performer for commercial and residential use above ground.

To get a sense of how to use Tables 1 and 2, the following examples should help:

Example 1

Q. What is the capacity of 3/4" type L copper tubing in gallons per lineal foot?

A. Looking at Chart 1, there is .0251 gallons of water in one lineal foot of 3/4" type L copper pipe.

Example 2

Q. Suppose a branch must supply water to a new master bathroom, consisting of a shower, roman tub, toilet, and two sinks. The pipe is Type M copper and the rated maximum gallons per minute of each valve is as follows:

Shower: 3.5 GPM
Tub: 5 GPM
Sink: 1.5 GPM x 2
Toilet: 1.5 GPM

Total Peak GPM flow: 11.5 GPM.

What is the minimum supply size serving the main branch trunk to avoid water hammer?

A. Realistically, the peak flow could be derated since it is unlikely that all faucets would be turned on at peak volumes simultaneously. Furthermore, since the shower, tub, and sink are served by both hot and cold water supply lines, this could also be factored into the derating. However, for the sake of example, let's assume a worst-case scenario of 11.5 GPM.

Using Chart 2, a 1" type M copper pipe can withstand up to 13.62 GPM flow rate without violating the 5 foot/second velocity. This would certainly work. However, by factoring in a reasonable derating and accounting for the split between the hot and cold water supply lines, 3/4" pipe would likely be satisfactory, allowing up to 8.07 GPM for both the hot and cold water supply lines.

Example 3

Q. A 1/2" Type L copper tube is used to supply a washing machine with a 6 GPM fill rate. Will this create water hammer when the machine valve turns on and off?

A. Looking at Chart 2, the maximum flow rate for 1/2" Type L copper pipe is 3.63 GPM. The proposed 6 GPM would increase the velocity to over 8 feet per second, a condition likely to cause water hammer.

Example 4

Q. What size should the main trunk line be from the water meter to the house to avoid water hammer under the following conditions assuming Type K underground copper supply line:

Sprinklers running @ 6 GPM
Dishwasher filling @ 3 GPM
Washing machine filling @ 6 GPM
Two showers running at 2.5 GPM each

Total peak demand is 18.5 GPM.

A. Looking at Table 2, a 1-1/4" supply line would just meet this requirement, providing up to 19 GPM at a 5 ft/s peak velocity.

Mitigation in Existing Homes

The above examples provide insight into new construction where there is total flexibility in sizing supply lines properly at the outset. But suppose you have an existing home and you are experiencing noisy plumbing that rattles, bangs, shutters or squeals? These symptoms may not all be related to water hammer and often there can be multiple problems that fool novice troubleshooters. Before you replace your plumbing lines, there are several troubleshooting alternatives starting with a few that are simple and relatively inexpensive.

Drain Water Supply to Recharge Air Chambers

If water hammer persists and you believe your home has built-in air chambers (true of most older homes), turn the water heater off or to "standby setting" and shut off the main household water supply. Drain the entire household plumbing system (and water heater) at the lowest point in the system. Turn on all faucets to make sure there is no vacuum that prevents the water from draining. This will ensure that the supply lines fill with air.

Once you are sure that there is no residual water in the supply lines, shut off all open faucets. Carefully restore the main water supply and slowly turn on the faucets at the end of each branch run. This process will restore water into the system, trapping fresh air in the risers. If the risers are clogged with mineral deposits and other muck, this procedure won't help much, unfortunately.

When the system is fully recharged, restore your water heater to its normal operating temperature range. This recharging procedure will have only a limited impact as air chambers typically become waterlogged over time, requiring a repeat of the process described above.

CAUTION!: When draining the water heater separately, the water temperature could be scalding (140-160 degrees) resulting in serious burns. Always wear protective clothing and protect your face and eyes with goggles. Be very careful when draining a water heater and carefully follow all manufacturer's instructions.

Install Low-Flow Fixtures

Since water hammer is correlated to total flow velocity, one solution in older homes is to replace existing fixtures with low-flow types or water restrictors. For example, replacing an old 4.5 GPM shower head with a newer 2.2 GPM version will cut the peak flow rate in half. Similarly, replacing tub and lavatory faucets or using flow restrictors could be enough to minimize water hammer.

Check Washers, Valves and Toilets

Sometimes other factors can create resonance in a water supply system which amplifies through the pipes. These include faulty washers in faucets or supply shut off valves. If nothing has changed in your home and suddenly you are experiencing noisy plumbing, try isolating the fixture that has the problem and inspecting the valve mechanism. Resolution to your problem might be as cheap as a five-cent rubber washer.

If the problem appears to be related to the toilet, you may need to change the ballcock, fluidmaster or fill valve. Or the shutoff valve to the toilet may have a bad washer.

Secure Loose Pipes

While this may not always be convenient due to poor accessibility of hidden pipes, long straight runs are generally the worst offenders. Where accessible, tightly secure all pipes at frequent intervals to minimize rattling against hard surfaces. While strapping will help to alleviate some of the rattling sounds resulting from water hammer, it does not address the water hammer condition itself.

Install Pressure Regulator

If your home does not have a pressure regulator and your water pressure is high (in excess of 60-80 PSI), adding a pressure regulator could help to reduce water hammer. By reducing household pressure to 40 PSI, you will retain sufficient pressure while reducing the likelihood of damaging water hammer. This should be done by a professional, licensed plumber.

Adjust Existing Pressure Reducer

Some people report a "squealing" noise in their plumbing. This should not be confused with water hammer. If your main water supply line already has a pressure regulator, you may need to adjust the set screw on the regulator to eliminate the squealing sound. If it's adjusted all the way down to the lowest pressure, this can create a condition called cavitation.

According to Utah State University's School of Engineering, "Cavitation is a liquid phenomena based on the formation and collapse of vapor cavities in the fluid passing through a valve. The vapor cavities begin to grow in low pressure regions such as areas of separation and collapse downstream of the low pressure regions. Cavitation can produce the effects of noise, vibration, and erosion or damage to the valve and downstream piping."

Alternatively, experts at HandymanWire.com advise, "if you have a shutoff valve prior to or after a pressure reducing valve, and they are of the washer variety, check it for a bad washer and make sure it is open all the way. If you can narrow it down to a watered valve and changing washers does not help, replace it with a ball valve."

Install In-Wall Water Hammer Arresters

This process can be more invasive and requires that you have access (or create access) to the fixture supply line where water hammer is most prevalent (such as a dishwasher, washing machine, icemaker, or other fast-acting valve). Water hammer arresters are similar to air chambers, except that the air pocket is fully isolated and sealed from the water, typically with a piston type plunger and lubricated O-ring. Water hammer arresters help to absorb the pressure shock wave, virtually eliminating water hammer. The Plumbing and Drainage Institute offers a comprehensive document on Water Hammer Arresters. Interested parties may download this document as a PDF file at: Standard PDI-WH201 Water Hammer Arrester Standard (3663 KB).

Several manufacturers make compact water hammer arresters for residential and commercial use. For example, Precision Plumbing Products makes convenient wall boxes for washing machines and ice makers. In addition, they offer handy "mini angle stop" versions that are easily accessible making them ideal for retrofit applications at sinks and toilets.  The version at the right, is known as the "mini-rester" and is made by the Sioux Chief Manufacturing Company. It is a cost-effective solution for a single valve, such as a washing machine. Other versions are available that either screw in or can be sweat soldered, such as the Hydra-rester. Typical prices for water hammer arresters range from $15 to over $125 each depending on capacity.

For optimum performance, water hammer arresters should be installed inline with the branch supply at the fixture tee with no intermediate bends. Furthermore, sizing must be done by a qualified professional working with the manufacturer. Failure to properly size the water hammer arrester will result in sub-optimal performance and wasted effort.

Table 1: Copper Pipe Size Guide



Type K

Type L

Type M



Cu Ft



Cu Ft



Cu Ft


1/4" .375 .305 .00051 .00379 .315" .00054 .00405 -- -- --
3/8" .500 .402 .00088 .00660 .430" .00101 .00753 .450 .00110 .00826
1/2" .625 .527 .00151 .0113 .545" .00162 .0121 .569 .00176 .0132
5/8" .750 .652 .00232 .0174 .667" .00242 .0180 -- -- --
3/4" .875 .745 .00303 .0227 .785" .00336 .0251 .811 .00359 .0269
1" 1.125 .995 .00540 .0404 1.025" .00573 .0429 1.055 .00607 .0454
1-1/4" 1.375 1.245 .00847 .0634 1.265" .00875 .0655 1.291 .00910 .0681
1-1/2" 1.625 1.481 .0119 .0894 1.505" .0124 .0925 1.527 .0127 .0951
2" 2.125 1.959 .0209 .156 1.985" .0215 .161 2.009 .0220 .165

Legend: OD = Outer diameter, ID = Inner Diameter, Cu Ft = Cubic Feet per foot, G/Ft = US Gallons per foot of pipe.

Table 2: Maximum Recommended Flow (GPM)

Copper Pipe
Nominal Dia



Type K

Type L

Type M

1/4" .375 1.14 1.21 --
3/8" .500 1.98 2.26 2.48
1/2" .625 3.39 3.63 3.96
5/8" .750 5.22 5.44 --
3/4" .875 6.81 7.53 8.07
1" 1.125 12.12 12.87 13.62
1-1/4" 1.375 19.02 19.65 20.43
1-1/2" 1.625 26.82 27.75 28.53
2" 2.125 46.80 48.30 49.50

Legend: OD = outer diameter; assumes max. velocity = 5 feet/second to avoid water hammer

Go to Table of Contents

Table 3: Typical Household Flow Rates

Appliance/ Use 

Typical Flow Rate (GPM); 80 PSI MAX 

Lavatory Faucet  0.4 - 1.5
Bath Tub  2
Roman Tub 3 - 5
Shower 1.6 -2.5 (older showers up to 4.5 GPM)
Kitchen Sink  1 - 2.5 
Dishwasher  2
Washing Machine

Source: U.S. Department of Energy

Go to Table of Contents

Table 4: Plumbing Fixture Units

Plumbing Fixture Description

Fixture Units

Combination Bath/ Shower  4
Whirlpool Bath  4
Shower 2
Lavatory  1
Clothes Washer  4
Dishwasher  1.5
Kitchen Sink  1.5
Pressure Range 30 to 45 PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 3-12 1-6 1-5 0-4
1" 12-25 6-17 5-13 4-12
1-1/4" 25-48 17-32 13-25 12-21
Pressure Range 46 to 60 PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 5-17 3-11 2-8 1-6
1" 17-36 11-25 8-20 6-18
1-1/4" 36-78 25-52 20-39 18-33
Pressure Range 60+ PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 6-20 4-13 3-10 2-8
1" 20-39 13-32 10-26 8-22
1-1/4" 39-78 32-74 26-54 22-43
Go to Table of Contents


Water hammer is a potentially serious condition that can result in noisy plumbing and premature failure of a residential or commercial plumbing system. Through proper up-front engineering and sizing of the supply lines -- coupled with attention to mechanical fastening during installation -- the destructive impact of water hammer can be minimized or eliminated altogether. Use of water hammer arresters in lieu of traditional air chambers can mitigate chronic water hammer problems in both new and existing construction. Always use a professional, licensed plumber or contractor when dealing with repairs to a water supply system, particularly where it connects to municipal water supply systems. Go to Table of Contents


"Water Hammer Arresters," Standard PDI-WH 201, Plumbing and Drainage Institute (pdionline.org)

"Water Hammer - How to Stop the Bang!," Ask the Builder, 1997.

"Bulletin 187 Installing Water Pressure Reducing Valves and Water Heater Expansion Tanks," Ask the Builder, 1997.

"What is Water Hammer?," diy-online.co.nz

"Water Hammer Arresters," Precision Plumbing Products

"Residential Water Hammer," Terrylove.com


"Why Do We Do It Like We Always Do It?" Karl D. Conley, CIPE

http://www.jessstryker.com/ - a great source of information on irrigation

www.pressure-drop.com - shareware software

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