Does A Tankless Water Heater Need A Filter? Yes, It Does!

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Does A Tankless Water Heater Need A Filter? Yes, It Does!

Your tankless water heater was not cheap. Don’t let it get ruined by sediment or scale. 

There are a number of ways to protect your investment, but none are better than the right filter for a tankless water heater.

You’ll add years to the life of your water heater and all the other appliances in your home.

Hard water wreaks havoc on a tankless water heater. If you don’t have a filter then you need to be doing yearly flushings to descale it.

If you have a well, then you absolutely have to have a pre-sediment filter to keep your tankless working.

If you don’t have time to read the tankless water filter reviews then take a look at the table below to see how the different types compare. Otherwise, read on for all the details.

Why You Need a Filter

Most people do not have filters for their home water. This is odd since most of the US has hard water from their municipality, and many people have wells. Even if you don’t have a tankless water heater it is very smart to have a filter in your house.

Read More!

If you do have a well and are looking at tankless water heaters then check out this article about how to use a tankless water heater with a well.

Hard Water and Scale Build-Up

Hard water will reduce the efficiency of just about every appliance that uses hot water in your house. In the case of tankless water heaters, you can lose about 30% of their efficiency with even the lightest buildup of calcium on the heat exchanger.

Scale buildup can happen even if your water is not particularly hard. You may only have a small amount of lime in your water, but it will wreak havoc on your appliances. 

In the case of scale, there are some filters that will reduce the lime in your water without needing a water softening agent. More on that later.

To know how hard your water is, call your municipality and ask them. They run frequent tests to determine water quality and will have that information.

If you have a well then refer to this map below.

Read More!

One of the downsides of having a well is that there is sediment and hard water. Read all the details about having well water vs city water to see if you think it’s worth it.

Water Softeners vs Conditioners

When water is hard, it has a lot of calcium and magnesium that have positively charged ions. To get rid of them a water softener will reverse the charge of the ions and effectively remove them from the water.

Part of the process uses salt. This can affect how the water tastes, so using a salt free water softener is my recommendation.

Instead of using ionization, they use a process called template-assisted crystallization. These actually are called water conditioners and not water softeners as the process is different.

A salt free water softener is ideal for tankless water heaters since there is no standing water in them. They also don’t waste as much water as a traditional water softener, require less maintenance and cost less to operate.

Watts Premier Scale Prevention and Water System

Watts Premier Scale Prevention and Water System
  • Chemical-free scale reduction  and protection converts hard minerals into...
  • High-capacity, 20-micron water filter removes chlorine taste and odor while...
  • Virtually maintenance free, no electricity, wastewater, control valve and...
  • Improves efficiency of all water heating devices and downstream plumbing...
  • Easily installed to the floor or wall using included mounting bracket;...


  • Lasts up to 250,000 gallons
  • 10 gallons per minute flow rate
  • Leaves water pH between 6.5 to 8.5
  • Works up to 75 grains per gallon hardness
  • No backwashing needed

With a capacity up to 250,000 gallons, you can save money and hassle with this water conditioner. The filter only needs to be replaced every three years for most households.

The OneFlow water system filters and softens the water for the whole house as it enters. This will help all of your appliances in addition to the tankless units. And it is much better on your sink and tub as it won’t stain or calcify the fixtures.

It requires no electricity so it saves money there. Plus it won’t waste any water while conditioning the incoming water.

If you have less than 75 grains per gallon then this is just the ticket. With up to 10 gallons per minute water flow rate, you can still use multiple fixtures without slowing the filter down.

Maintenance is easy as it requires no backwashing, either.

It also includes a 20micron radial carbon block cartridge to remove tiny particles and sediment.

AFWFilters Metered Whole House System

AFWFilters Metered Whole House System
  • AFWFilters install kit for easy installation
  • Made in the USA, AFWFilters easy to install, easy to use
  • The Fleck 5600sxt digital metered, on demand valve. The newest 5600 model...
  • Fleck 5600SXT Digital Control Head with bypass valve and 1" threaded...
  • 10" x 54" pentair tank, 15” x 34” brine tank with safety float system,...


  • 48,000 grain 
  • Will treat up to 12 Gallons Per Minute
  • Intelligent Regeneration saves water
  • Digital display also saves settings
  • Easy to install

Installing the Fleck water softener is so easy and can be done yourself. Once installed, it is ready to go to soften water for the whole house. This will protect more than just your tankless water heater.

The flow rate at which it can filter the water is 12 gallons per minute. This is a very good GPM for a large house as you can use several fixtures at once and still get soft water.

One of the problems with water softeners is that they waste quite a bit of water. Thanks to Intelligent Regeneration, it will calculate how much water is being used in the house and if there is an increase in water demand, the system modifies its settings.

A digital display helps to set the filter for efficiency. There are settings for your water hardness and the computer will set the filter for automatic regeneration.

There is almost no maintenance required for this water softener for tankless water heaters. Every few months the filter needs to be replaced. And that is very easy to do.

Eddy Electronic Water Softener Alternative

Eddy Electronic Water Softener Alternative
  • WHAT EDDY DOES: Eddy is a NO-SALT household electronic water descaler, far...
  • WHO EDDY IS FOR: Eddy is for anyone who wants to reduce or eliminate the...
  • EASY DIY INSTALLATION: Simple step-by-step guide supplied with Eddy whole...
  • DESCALER BETTER THAN SOFTENER: The Eddy ED6002P electric water descaler...
  • MONEY BACK GUARANTEE: 365 day “satisfaction or money-back” warranty and...


  • 12 month no questions asked warranty
  • Incredibly easy installation
  • Uses no salt and leaves healthy minerals in the water
  • Works up to 20 grains per gallon
  • Eco friendly

A third type of water softener is the electric type like this one by Eddy. It is not exactly a water softener as it does not change the TDS of the water. 

It is an ingenious device that exposes the running water to an ever-changing electromagnetic field. This changes the scale within the water preventing it from clinging to the surface of your pipes or appliances.

There are no filters to change, no maintenance to perform and no build up of any calcium or lime that needs to be discharged.

If you live in an apartment and are not able to install a filter to the whole house, then this is a great alternative. There are two cables that get wrapped around the pipes of the incoming water. It can be mounted anywhere because of this. 

Using an electronic water softener with a tankless does not mean that you don’t have to flush it. There will be some residue on the heat exchanger, so you’ll still need to do a flush occasionally. 

The nicest thing about this hard water treatment is that it uses no salt, wastes no water and is totally ecofriendly.

Your electric bill will go up slightly, but not by much. And, it will be worth it to not deal with the breakdown of your appliances like a tankless water heater.


If you have a well then it is an absolute must to have a pre-sediment filter at the very minimum. A tank storage system can handle some sediment since it will fall to the bottom of the tank.

Since the water goes right from the source to the heat exchanger in a tankless, there is no means of escape for the sediment. Your tankless water heater will get clogged within days. Not only does this mean your hot water will be affected, but your on-demand heater will die very quickly on you.

Even some municipal water supplies can have excess sediment or other debris in it. I recommend having a filter even if you don’t use well water.

 iSpring Rotatable Head, Pressure Gauge

iSpring Rotatable Head, Pressure Gauge
354 Reviews
iSpring Rotatable Head, Pressure Gauge
  • Press Gauge design. The whole house spin down sediment water filter has...
  • Flushable and reusable. Take considerable workload off finer filters that...
  • Easy Installation. System can be installed in any direction thanks to the...
  • Long-lasting materials. The steel mesh filter cartridge and housing can be...
  • Excellent customer service. iSpring provides you lifetime support with high...


  • Stainless steel mesh filter screen rated at 50 Micron
  • Flushable and reusable for long filter life
  • Can be installed in any direction
  • ¾ inch threads

The iSpring is the best sediment filter for well owners as it can remove particles down to 50 microns. Most particles in well water are not usually smaller than 50 microns, so the filter lasts longer. When the mesh is too fine, it tends to clog up faster.

There is a scraper inside that will clean the mesh for when it does inevitably get blocked by the particles. Almost like a wiper blade, it scrapes off all the sludge to keep the water flowing. All it takes is turning the filter by hand. It only takes a few seconds to do.

The filter doesn’t need to be replaced as often as others, saving time and money. The upfront cost of the filter is higher than some others, but it saves money after its first year of use since you don’t need to buy replacement filters.

The size of the mesh can be adjusted so you can go a while before needing to scrape the container. Your choices are at 1000 microns to 50 microns. If your sediment is not so fine, then choose a larger micron capability so the water pressure does not drop much. You’ll get about two years with the larger micron setting and a year to two set at 50 microns.

Opening the bottom of the filter will allow you to get rid of the larger sediment as it falls to the bottom of the trap. And it can be mounted in any direction. The water connections are on the side of the filter and can be turned in any direction making installation easy. There are ¾ or 1-inch connections for compatibility. 

Aquasure Carbon Dual Purpose Water Filter

Aquasure Carbon Dual Purpose Water Filter
  • Aquasure Fortitude V Series 25 micron sediment / carbon dual purpose water...
  • The unique design polypropylene sediment and GAC carbon make it ideal to...
  • A perfect pre-treatment filter for residential home who seeks an affordable...
  • 1" FPT inlet and outlet minimized water restriction while the included...
  • All Aquasure whole house water filter comes with one year manufacturer...


  • Protects from particles down to 25 micron
  • Absorbs chlorine and odors
  • Filters up to 50,000 gallons of water
  • Very easy to install

This Aquasure pre sediment filter works like a water filter trap. It has a membrane that filters out particles down to 25 microns in size. Then the contaminants are trapped in the carbon core. 

It has a dual process system. The outer layer is what screens out the particles and sediment leaving the water clear. Inside, the chlorine, off tastes, rust and other chemicals are trapped. Not only is your water free of sediment so your tankless water heater runs smoothly, but your water tastes better and is healthier.

It is super easy to install and only takes a few minutes. One word of warning is that it can only support water pressure up to 90psi. Not a problem for most people out there. Especially well owners as pumps rarely get over that mark.

The filter will need to be replaced after 50,000 gallons. How long this takes depends on your water demand and how many people use the water. For the average size family, plan on replacing it every 6 months or so.

Read More!

You can have a tankless water heater when you have hard water by following the steps in that article. Click the link to learn more.


Which of these is the best filter for tankless water heaters is dependant on your circumstances and what you need the filter to do. One thing is certain, any of the filters in the reviews above will do whatever it is you need. 

Choose according to your situation and any of them will get the job done.

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