How a Sediment Filter Can Protect Your Tankless Water Heater

Water Softeners Tankless Maintenance

You may have heard about the importance of using a sediment filter, but did you know the role they play in keeping your tankless water heater healthy? On-demand systems must be supplied with quality water, especially since they don't have the same defenses as traditional tank style water heater. 

If the incoming water supply is full of debris, a tankless unit will quickly breakdown and require service.  A properly maintained and installed on-demand system can have a service life of up to 25 years, but with poor quality incoming water, disaster can strike within days!

One of the simplest ways to protect your unit is to make sure that the water entering your tankless is free of debris and excessive minerals. This can be done with the use of sediment filters, water softeners, and regular flushing. 

Sediment​ and Tankless Water Heaters

Sediment is simply any solid material, such as sand or debris, that collects within water. It frequently enters the home's incoming water supply thru municipal water mains and home well systems, but it can also occur from the minerals in the water itself that precipitate out when the cool water is heated. 

​Local water companies periodically open fire hydrants to help clear the sediment from their water mains. Unfortunately, sediment is part of our everyday water source, and some areas are more prone than others.

A traditional water heater will collect and "store" the sediment at the bottom of the tank. If not properly maintained, the tank will eventually develop a leak and the water heater will need to be replaced. 

Tankless systems are far less forgiving when dealing with sediment. They aren't capable of accumulating the incoming sediment, and with only the inlet filter for protection, the unit is left nearly defenseless and stands vulnerable to the incoming water supply.

​If the inlet filter fills with debris and clogs, the tankless unit will malfunction and require service.​ Although all tankless systems have an inlet filter, it should never be relied on to protect your unit from sediment. Think of the inlet filter as a last line of defense for your water heater.

Incoming Water Quality

The quality of the incoming water supply should be carefully evaluated and addressed since it will directly impact the service life and performance of your tankless water heater.

​Water must be potable, free of sand, dirt and corrosive chemicals, as well as any other contaminates. Flushing a tankless water heater is a critical task that should occur on a regular basis. Failure to flush the limescale build-up from your tankless unit will prevent your water heater from running at it's peak efficiency, as well as shortening it's service life. Check out our post on How to Flush Tankless Water Heaters.

  • Most manufacturer warranties do not cover the replacement of the heat exchanger due to  damage from hard water or other water quality related issues. 

​Regardless of your water quality, we highly recommend installing a sediment filter. Although,  sediment filters won't take the place of regular maintenance, they will add an additional layer of necessary protection for your tankless system. 

Sediment Filters

Tankless Water Heater Maintenance

A sediment filter does exactly what the name implies. It filters the sediment from the water. Keep in mind that these filters are effective at removing sediment by straining the particles from the water, however, they DO NOT remove chemicals or heavy metals. 

A sediment filter is installed on the incoming water supply, and filters the water BEFORE it enters the tankless unit. Many homeowners choose to purchase a whole-house sediment filter which is installed on the home's incoming water supply. These systems are particularly effective since they will not only filter the water entering the tankless unit, but also the household water.

Overtime, the filter cartridges will clog and prevent water from passing thru the filter. Some systems recommend that the filter cartridge is changed monthly, others recommend every several months. But the frequency of changing the filter really depends on the amount of sediment within your water supply.

How Sediment Filters are Rated

​A filtration cartridge is rated by the size of particles the filter is capable of removing. This measurement is called a micron. As an example, a 5-micron filter is rated to capture particles as small as 5-microns.

The lower the micron rating the smaller the particle the filter is capable of removing. Keep in mind, that the smallest micron rating isn't always the best choice, and the amount of sediment varies by geographical location. Experiment until you strike a balance between acceptable water flow, reasonable lifespan, and adequate particle filtration. ​In most cases, a 20-micron rating is adequate.

Filtration effectiveness is measured in terms of nominal and absolute. These ratings specify the amount of particles, at the desired micron rating, that should be filtered out of the water. See the chart below for details. 

For most purposes a nominal filter will be sufficient. However, if you are concerned about filtering out bacteria or cysts you should use an absolute filter.

Nominal vs Absolute Micron Ratings


Nominal Micron Rating

  • Should filter out 85% of the particles of the specified size.
  • Most commonly used for sediment filtration. 

Absolute Micron Rating

  • Should filter out 99.9% of the particles of the specified size. 
  • Used when very high grade water is required, or the need to remove a parasite from the water, such as Giardia

​For example: If you purchased a filter that is rated 5-micron nominal, you can expect this filter to remove 85% of the particles within the water that are 5-microns or larger.

But if you purchased a filter that is rated 5-micron absolute, it should filter out 99.9% of the particles the size of 5-microns or larger.

Types of Sediment Filters

The most common sediment filters are radical flow cartridges, where water flows from the outside of the cartridge to the inside, and the entire filter surface area is used to filter the water. There are two main types of radical flow filters used as sediment filters:

Depth Filters - Incoming water is forced thru the sides of these filters. The sediment particles are trapped as the incoming water moves from the outside into the center of the filter.

Many depth filters are designed with several layers that catch different sized particles. The inner layer will catch the micron size that the filter was rated to trap. These filters are popular because they are effective at filtering out a variety of particle sizes. 

These depth filters are rated for 10-microns and are available on Amazon.

There is also a wound string version available.​

As an example, a graduated 5-micron filter may be designed so that the outer layer will catch particles the size of 50-microns. The 3rd layer, 25-microns. The 2nd layer, 10 microns, and the inner core will catch the particles that are 5-microns in size.

Surface Filters - ​Are commonly called pleated filters because they have a thin pleated sheet that traps the particles on the surface. Because of the accordion-shaped design these filters actually have more surface area to trap sediment than depth filters. Some surface filters can be cleaned and reused.

These surface filters are available thru Amazon.

 Depth vs. Surface Filters


Depth Filters

Surface Filters

  • Capable of holding more debris.
  • Excellent for filtering multiple sized particles. 
  • Capable of filtering more sediment without losing pressure.
  • Many are designed to trap larger particles on the surface of the filter and smaller particles within the filter.
  • Offers more filtering surface area.
  • Higher capacity to filter particles of a uniform size.
  • Can often be rinsed and reused.
  • Water pressure will be influenced by the amount of debris build-up on the filter. 

This whole house sediment filter, which is available thru Amazon, is capable of filtering 15,000 gallons of water. It is inexpensive and relatively easy to install.

A variety of filters are available to purchase to customize the degree of filtration. 

Conclusion: Our Final Thoughts 

All tankless water heaters should have a sediment filter installed on their incoming water line. These filters will protect your unit from unexpected debris entering your tankless. They are inexpensive and easy to maintain and well worth the investment.

Although a sediment filter can be configured to filter only the incoming water reaching the tankless water heater, we recommend installing a whole house system. A whole house sediment filter will not only protect your tankless, but it will also protect your other water-using appliances, as well as shower heads and faucets.