a water heater without a tank on the wall of the kitchen

How to Quiet a Tankless Water Heater

Regardless of what you may think, tankless water heaters also get noisy. Even if the noise isn’t loud and doesn’t necessarily mean that there’s a problem causing it, it’s wiser to check and address any issues.

What are the typical causes of noisy tankless water heaters?

Tankless water heaters can make all kinds of noises when running at first and heating water, but the level of noise doesn’t disturb you nor poses a concern. Any noise happening when your tankless unit isn’t running may be caused by the vacuum siphoning water, leading to noise and vibration.

Most of the time, you should get the plumber to take a look at the valves in the water line so that no other problems develop, altering the flow of water or the performance of your unit.

Another standard issue that causes loud noises in tankless water heaters is a dirty flow sensor. The sensor controls the amount of gas sent to the unit. A blocked or improper ventilation, and even a defective or wrongfully set pressure valve can also make your tankless water heater loud.

Gas-fired tankless water heaters can also make various sounds while firing up and heating the water. Most of the time, the levels should be lower than 90 decibels.

Side note: You can use a decibel meter for identifying the level of noise from your tankless water heater. It’s easy to do it if you have a smartphone. You can download a free decibel meter app and measure the decibel output on your own.

Should your tankless water heater cause a noise even if it’s not running, there can be several causes. Any now and then, a source is siphoning water from the line and causes a vacuum. A weird groaning sound from the pipe or your tankless unit may also occur as you’re flushing the toilet. It’s weird, especially since the toilets don’t use cold water.

Identify the noise- the first step when fixing the noise situation!

When your tankless water heater is loud, the very first thing to do is to identify the source. A rumbling noise, a humming noise, or a banging are all signs of different problems with your tankless water heater. It’s essential to be able to describe the sound (you can even record it with your phone) to the plumber. It helps him find the problem a lot easier.

Here are the common causes and the fixes to try:

  • Sediment buildup

More often than not, the typical reason for a noisy tankless water heater is the buildup of sediment within the system. Even if water doesn’t get to stay in the system, it still may lead to sediment buildup. It contains plenty of minerals (calcium and magnesium are the most concerning) that eventually build up.  Moisture can actually get trapped under the coating, boiling as the element is heating. The result is popping, hissing, or cracking noise. As the heated water comes in contact with the sediment, you can hear a popping noise (it’s actually the sediment breaking).

Solution: The sediment isn’t going to go away on its own. You need to flush the water heater on a regular basis. Once a year should be enough, but in regional with tough water, the flushing should be performed a lot more often.

You can also prevent the sediments to buildup by installing a water softener along with your tankless unit. Even if the risk for minerals to build up isn’t eliminated for good, it can still help with the performance and makes flushing a lot more efficient.

  • Loose parts

A humming noise, while you’re using the unit, is a sign that a component of the system is free. As the tankless water heater is running, some loose parts may vibrate, leading to the noise. In the case of electric tankless units, for instance, the heating element is placed on the side of the water heater. When the part is loose only a bit, the water heater will make a sound when running. It’s not dangerous per so, but slightly annoying.

Solution: Simply tighten the loose parts for fixing the problem and the sound.

  • Water hammers

The sound  water makes while getting through pipes and stops all of a sudden is known as “water hammer.” It’s similar to an impressive banging noise. This time it’s not the tankless water heater causing the sound, so the solution is somewhat tricky. Just because you hear the water hammer near the tankless water heater doesn’t mean that the unit is the cause, though.

Solution: Get in touch with a plumber and have him install a “water hammer arrestor” in the area where the water hammers happen.

  • Other problems

We should remind you once more that it’s perfectly normal for on-demand water heaters to make a sound while firing and heating the water. For many models, the noise level is around 55 decibels. One of the common reasons is the installation, with wall-mount and encased in protective boxes as primary options. When the unit is installed close to a window, the chance for you to notice the water heater while igniting is higher.

Solution: You need to check the origin of noise and see if it’s the vibration of the unit against the wall or if it echoes within the protective box. You can absorb some of the sounds and lower the vibrations and echoes. Should your water heater be exposed on an outside wall (it’s not enclosed), you can quickly put some foam or rubber matt between the wall and the unit.

If the unit is inside a protective box, you should insulate the inside of the box with materials used in the auto industry for audio insulation.

What’s the takeaway?

Some noise is always typical for tankless water heaters, and you should check to see which is the level of noise for your particular model.

When the noise is loud, and you can no longer focus because of your tankless water heater, you should take action and find out the cause of the sound. Even if it may not be a severe problem behind, there may still be issues that cannot go without fixing. The best thing to do it give the plumber a call for future actions!

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