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Sediment Filters: Why Your Tankless Water Heater Needs One


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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 heaters. 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 tankless 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 through municipal water mains and home well systems, but it can also develop 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.

Tankless Water Heater Maintenance

Tank-Style vs Tankless

A traditional tank-style water heater collects and "stores" 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. 

But 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 water heater will malfunction and require service. Although all tankless systems have an inlet filter, it should never be relied on to protect your heater 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 system will prevent your water heater from running at it's peak efficiency, and it will shorten 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. And since the upfront cost of replacing a tankless system far exceeds the expense of replacing a tank-style water heater you could be out some serious cash.

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. 


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Sediment Filter Rating System

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 water heater. 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 system, but they also filter the household water.

The filter cartridges will need to be changed regularly as they will clog and prevent water from passing through. 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.

Particle Size Rating (Micron)

The 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. In most cases, a 20-micron rating is adequate, but you should experiment until you strike a balance between: 

  • Acceptable water flow
  • Reasonable lifespan
  • Adequate particle filtration

Nominal vs Absolute Micron Ratings

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. 

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

Nominal Micron Rating - Nominal filters are most commonly used for sediment filtration, and they should filter out 85% of the particles of the specified size. As an 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.

Absolute Micron Rating - Absolute filters are used when very high grade water is required, or there's a need to remove a parasite from the water, such as Giardia. These filters should filter out 99.9% of the particles of the specified size. For example: 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.


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Types of Sediment Filters

The most common sediment filter is the radical flow cartridge. This is where the 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 and surface filters.

Depth Filters

Incoming water is forced through the sides of a depth filter. 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 outer layers catching larger particles, while the inner layer is designed to catch the micron size that the filter was rated to trap. As an example, a graduated 5-micron filter may be designed so that the outer layer catches 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.

There are a variety of styles available, the most common are the wound string and poly block type. Depth filters are very popular because they're inexpensive, yet effective at filtering out a variety of particle sizes.

Advantages of Depth Filters

  • Depth filters are capable of holding more debris than surface filters.
  • They are excellent for filtering multiple sized particles.
  • Are capable of fitering more sediment than suface filters without losing pressure.
  • Many depth filters are designed to trap larger particles on the surface of the filter and smaller particles within the filter.

Depth Filters

DuPont WFPFC5002 Universal Whole House Poly Block Cartridge, 2-Pack

Surface Filters

Surface filters are commonly called pleated filters becaue they have a thin pleated sheet that traps the particles on the surface. Suprisingly, surface filters can actually trap more sediment than depth filters. This is because their accordion-shape design provides more surface area. Some surface filters are designed to be reused after being cleaned.

Advantages of Surface Filters

  • Surface filters offers more filtering surface area than depth filters.
  • Have a higher capacity to filter particles of the same size. 
  • Frequently are designed to be rinsed and reused.
  • One main disadvantage is that the water pressure will be influenced by the amount of debris build-up on the filter.

Surface Filters

DuPont WFPFC3002 Universal Whole House Pleated Poly Cartridge, 2-Pack


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Sediment Filter Housing

In order for a sediment filter to work, it needs a housing. The housing attaches to the incoming water supply and allows the water to pass through before entering your tankless water heater. When it's time to change your filter, it's located within the housing.

Some manufacturers require the homeowner to use the same brand of filters as the housing for it to filter properly, so choose your housing and filters carefully. We recommend purchasing the DuPont Whole House Filtration System. It's designed to filter 15,000 gallons of water between filter replacements which is large enough to protect all of your water appliances and fixtures from sediment.

It's inexpensive, relatively easy to install and there are a variety of filters available which will allow you the abiltiy to customize the degree of filtration.


DuPont Whole House Filtration System

DuPont WFPF13003B Universal Whole House 15,000-Gallon Water Filtration System


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Final Thoughts

Sediment filters are inexpensive and easy to maintain should be installed on the incoming water line of all tankless water heaters. They are an important line of defense when it comes to protecting your water heater from unexpected debris entering the tankless system and causing unnecessary damage and wear. 

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

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