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Sediment Filters: Why Your Tankless Should Never Be Without One

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A sediment filter should play a big role in your water heater maintenance routine to ensure your tankless water heater is healthy. Incoming water frequently brings sediment into the home's plumbing, and when the debris enters a tankless unit, it can quickly breakdown and require service.  

A tankless unit that is properly maintained can have a service life of over 20 years, but if it is supplied with poor quality incoming water, the unit can develop major problems within days. 

5 Glasses being filled with water

Sediment and Tankless Water Heaters

A simple and effective way to protect your tankless water heater from the harmful affects of sediment  is to use a pre-filter that will remove the debris before it enters the unit.

Regular flushing, water softeners and sediment filters are all effective tools to help keep your on-demand unit healthy and working effectively. This article will focus on sediment filters.

Yellow caution tape

Dangers of Sediment

Sediment is any solid material, such as debris or sand that collects within water. As water enters the home's incoming water supply it is frequently carrying sediment from the municipal water main or a home-well system. To help clear sediment from water mains, local water companies open fire hydrants periodically to flush the debris from their pipes.

How Water Heaters Handle Sediment

Traditional tank-style water heaters are able to tolerate sediment to a certain extent. When sediment enters the tank it settles at the bottom. However, if the sediment isn't flushed during maintenance, the tank will begin to rust and eventually leak. The only solution when this happens is to replace the water heater. 

A tankless water heater's only line of defense from sediment is the inlet filter, which is a small mesh screen that filters the water before it enters the unit. Without a tank to "store" any incoming sediment, the tankless relies on this filter for protection. If the inlet filter isn't cleaned regularly and fills with debris, the tankless unit will malfunction and require service.

Think of the inlet filter as the last line of defense for your water heater. This small filter should never be relied on to protect your tankless water heater from sediment.


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Quality of Incoming Water

The quality of the incoming water supply will directly impact the performance and service life of a tankless water heater. When water enters your heater it must be:

  • Potable
  • Free of sand, dirt and corrosive chemicals
  • Free of other contaminates

Limescale is caused when minerals within the water separate and form a scaly layer within your tankless. Flushing your tankless on a regular basis will keep your unit running at it's peak efficiency and help it achieve it's expected 20-year service life.

Installing a sediment filter and in some cases, a water softener, can help give your tankless a additional layer of protection.

Manufacturer warranties do not cover the replacement of a heat exchanger (the most expensive part) if it was damaged due to water quality related issues.


Using a Sediment Filter

Installing a sediment filter on the incoming water line will protect your tankless water heater.  Water will flow thru the filter BEFORE it reaches the tankless system, and just like the name implies, a sediment filter, simply filters the sediment from the water.

You may choose to use a sediment filter for the water that flows into the water heater, or install a whole-house system that will filter the all of the home's incoming water.

Sediment filters only strain particles from water. They DO NOT remove heavy metals or chemicals.

There are filter cartridges that need to be changed periodically for the sediment filter to be effective. Overtime the cartridges will clog and prevent water from passing thru. The most common recommendation for changing the filter is monthly, but ultimately, the decision should be based on the amount of sediment within your water supply. Some areas may need less frequent filter changes, while others may need more. 

Sediment filter in a clear plastic case

 Sediment Filter Buyers Guide

When purchasing a sediment filter system there are 2 main things you need to know:

  1. The filter rating
  2. The type of filter

Sediment Filter Ratings

Cartridges are rated by the micron size of the particle the filter is designed to remove. For example, a 5-micron filter cartridge is rated to capture particles as small as 5-microns . . . anything smaller that 5-microns will pass thru the filter. 

The lower the micron rating, the smaller the particle the filter is designed to capture. It's a good idea to experiment with different filter sizes until you find a size that works best for your situation. The smallest micron rating isn't necessarily the best choice. Generally, a 20-micron rating is the best fit.

Try a Variety of Filters

The best way to find the right filter rating for you is to experiment until you strike a balance between:

  • Acceptable water flow
  • Reasonable lifespan
  • Adequate particle filtration

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Filtration Effectiveness: Nominal vs Absolute

Nominal and absolute are the terms used to measure the effectiveness of a filter. These ratings determine the size of particle and the amount of particles that is filtered from the water. 

In most situations, a nominal filter will work fine. However, an absolute filter should be used to filter out bacteria and cysts if you are in an area where this is a concern. 

Nominal Micron Rating

  • Filters out up to 85% of the particles at the specified micron size.
  • Frequently used for sediment filtration.
  • If your filter was rated 5-micron nominal, you can expect it to remove 85% of the particles within the water that are 5-microns or larger.

Absolute Micron Rating

  • Filters out up to 99.9% of the particles of the specified micron size.
  • Generally used when high grade water is needed.
  • Also used to remove parasites from the water. Such as giardia.
  • If your filter was rated 5-micron absolute, you can expect it to remove 99.9% of the particles within the water that are 5-microns or larger.
Man standing in front of a chalk drawn balance

Sediment Filter Types

When water flows from the outside of the filter to the inside it is called a radical flow cartridge. These cartridges are the most common sediment filters because the entire filter surface area is used to filter the incoming water.

There are 2 main types of radical flow filters available:

  1. Depth Filters
  2. Surface Filters

Depth Filters

  • Incoming water is forced thru the sides o the filter.
  • The sediment particles become trapped as the water flows from the outside into the center of the filter.
  • Depth filters are excellent for filtering multiple sized particles.
  • They are designed to hold more debris.
  • They are designed to filter more sediment without losing pressure.
  • Many are designed to trap larger particles on the surface of the filter and smaller particles within the filter.
DuPont WFPFC5002 Universal Whole House Poly Block Cartridge, 2-Pack

Depth Filters

Depth Filters are capable of filtering more sediment without the loss of water pressure.

Surface Filters

  • Also known as pleated filters because of the thin pleated sheet that traps the particles on the surface.
  • Surface filters actually have more surface area available to trap sediment than depth filters because of their accordion-shaped design.
  • Many surface filters can be rinsed and reused.
  • They are capable of filtering a higher capacity of particles of a uniform size.
  • Water pressure will be negatively influenced based on the amount of debris build-up on the filter surface.
DuPont WFPFC3002 Universal Whole House Pleated Poly Cartridge, 2-Pack

Surface Filters

Surface Filters have a pleated design which can capture more particles of a uniform size.

We strongly believe that a sediment filter should be installed on a tankless water heater's incoming water line. It's an inexpensive and easy way to protect your unit form unexpected debris entering the system.  

Another option, that would protect all of your water-using appliances and your home plumbing, would be to install a whole house sediment filter. 


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Whole House Sediment Filters

There are also whole house sediment filter systems, with a variety of filters available to customize the micron size filtered.

They are generally inexpensive and relatively easy to install and is capable of filtering 15,000 gallons of water. 

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

Whole House Filters

Whole House Filtering Systems tend to have a higher capacity since they filter all of the home's incoming water.

This video covers sediment filters and can help answer any additional questions you may have.

Watch the Video


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