Will an Expansion Tank Stop Water Hammer?

AllClear 9:36 pm

Will an Expansion Tank Stop Water Hammer?

You might think that the term “water hammer” sounds like the name of a villain from a comic book, and you’d be right. However, it’s just the villain inside of your plumbing pipes. Just because you haven’t heard of it, doesn’t mean that it’s not common, complex, and something you might have already experienced. If you’ve listened to thumping, pounding, or even banging when the water gets turned on and off, you’re undoubtedly experiencing its effects. So, will an expansion tank stop water hammer? Let’s find out.

What is Water Hammer?

The pipes in your home make a lot of noises, for a lot of different reasons. Water hammer has a distinct sound that happens for a specific purpose. Typically it occurs due to something called hydraulic shock. When you turn the faucet, or any plumbing appliance or fixture, off quickly the water moving through your pipes to come to an immediate halt. This creates pressure that has to go somewhere. So it vibrates through the pipe until it dissipates, creating what we call water hammer. It’s the shock of the unexpected action that creates a loud hammering noise in your pipes.

Will an expansion tank stop water hammer - hammer

Water hammer is more than an annoying sound. It can cause damage to your pipes. If pipes are older and wearing thin or have a bad joint, a pipe may burst due to water hammer. Prolonged water hammer can actually cause weakening of the pipe as well. So, while not an emergency, water hammer is something that should be addressed.

Some plumbing systems solve the water hammer problem with air chambers. These absorb the shock coming from sudden change in water flow, preventing the banging sounds in your pipes. Air chambers are usually hidden behind walls, so it is hard to say if your home has them. They can fail due to something called “water logging”.

Will an expansion tank stop water hammer - watterlogging

Fortunately, there is a DIY fix for waterlogged air chambers. Before you do anything else, try this simple fix to see if you have air chambers to come to the rescue:

  1. Turn the water off to your home. This is usually in the garage or at a meter box by the road. You may need a special tool. Of course a plumber can help you out but you can also try the fire department. They usually have water keys and may be willing to help if there aren’t any emergencies.
  2. Open the highest/furthest fixture and the lowest/nearest in your house. Whichever faucet is furthest away from your meter, open it now to drain all of the water out of the system. This may be a hose bib on the back of your house, a second story bathroom, or your kitchen sink. The lowest is usually going to be a hose bib on the front of your house, the bottom floor bathroom, or the kitchen faucet. We are replacing all of the water in your system with air.
  3. With faucets still open, turn the water main back on. The faucets will sputter and spit, but that is the pipes re-pressurizing with water. The pipes should fill back up, but not the air chambers. We have essentially “restarted” or “reset” your air chambers.

Modern Fix for Water Hammer

Air chambers are a bit passé. Today, water hammer is usually fix with a water hammer arrestor. This is a localized solution, meaning it will be installed at the fixture causing the problem. They work similarly to an air chamber, with some extra wiz-bang technology that keeps them from failing the same way that an air chamber can.

Some water hammer arrestors are simple to install, like the ones made for washing machines. They screw on, similar to a garden hose, right at the water connection.


In general, if it is a faucet or a sink that is causing water hammer and you don’t want to pay for a plumber or special parts you can just be a bit more careful with how you close the tap. Slow down the close, stop the hammer. It’s that simple.

Other Bumps in the Pipes

High water pressure is a problem in the Upstate and can create the high pressure conditions that cause water hammer and other pipe noises. Squealing, shaking, and other bumps in your pipes are all signs of possible high water pressure. Unchecked water pressures, especially those exceeding 100 PSI can void warranties, increase your water bill, and wear out your pipes and fixtures very quickly.

Loose pipes can make a racket in the walls. Not technically water hammer, it’s still a noise you want to stop. Strapping can typically fix vibrating or shaking pipes. Just be careful about the materials you use – try to match the strap to the pipe type. Galvanized or steel does not mix well with copper. There is a chemical reaction that will cause your pipes to fail.

What is an Expansion Tank?

Depending on how old your home is, you might not know what an expansion tank is, and that’s okay; you have us for that. In decades before, they weren’t required as a necessary part of plumbing like they are today. Current code, focused on stopping the backflow of water into the system, requires expansion tanks so the water from thermal expansion has somewhere it can go. This might mean that your plumber installs one when replacing your water heater.

Will an expansion tanks stop water hammer

Think of them as a small boiler or tank that sits on top of, or close to, your water heater. It’s used, essentially, to control water pressure. The tanks come in a range of sizes, and the one you require would depend on your water pressure, heating temperature, and your water heater itself. The tank that has been installed at your water heater absorbs any additional water into it because of thermal expansion, so water pressure gets minimized.

Will an expansion tank stop water hammer – and other benefits

Back to our original question – promise we are getting around to answering it. Will an expansion tank stop water hammer?

At its core, an expansion tank is there to absorb water and backwards pressure. So, in some cases – depending on the root cause – it may improve water hammer.

Will an expansion tank stop water hammer - yes

Owning a water heater is a necessity, but thermal expansion adds pressure to the tank and your system. There are a few ways that having an expansion tank can help to alleviate and prevent troublesome plumbing headaches. Let’s take a look at a few of them to help you understand how they work a bit better.

  • Extended Water Heater Lifespan: As the temperature of water increases, so does the volume of water, which leads to water pressure issues that could cause a string of expensive plumbing problems. If there’s nowhere for the extra water to go, stress gets applied to the water tank’s valves and seams that would otherwise get absorbed with the help of the other tank.
  • Less Plumbing Repairs: High pressure that gets caused by thermal expansion can have a severely negative impact on not just your water heater, but your entire plumbing system. The stress on the system could lead to leaky pipes, problems with the sinks and toilets, and of course, that hammering. This extra tank reduces the need for repairs by providing somewhere for the extra water volume to go and alleviates pressure. So, if you ask us “will an expansion tank stop water hammer?” The answer is yes.
  • Maximize Your Hot Water: Having this type of tank allows you to maximize the hot water that is available to you, and makes your water bill cheaper, too. When you turn on your hot water tap, instead of pulling water from the water heater, it removes it from this extra tank first. So, you get more hot water, and you’re not wasting any, either.

Because water hammer is difficult to diagnose, if the simple DIY fix mentioned above doesn’t work you should consult a licensed plumber. There are many variables that need to get taken into consideration, and things could backfire should an incorrectly sized expansion tank get installed. There is a range of sizes that are available, and the right tank needs to get selected.

If you have further questions about water hammer (also known as a fluid hammer or hydraulic shock), expansion tanks, thermal expansion, or generally think something could be happening with your pipes, then reach out to us. Our friendly staff is available to answer your questions and provide you with current code and experienced knowledge to solve all of your plumbing woes.

Article Author: Anja Smith

Managing Partner

Anja Smith is the author behind the All Clear Plumbing blog. She also writes regularly for Plumber Magazine, TradeBizToolbox.com, and on Medium.