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Does Your Tankless Water Heater Need a Filter?

However, one question which may not be so apparent is how these heaters deal with sediment in the water supply.
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Some modern models have built-in filters, but most have little or no protection against incoming particles. For this reason, it’s best to invest in an inline filter for your tankless heater.

Benefits of an Inline Filter

There are quite a few reasons for adding a filter to your tankless water heater system that you might not be aware of. This is because tank heaters inadvertently deal with incoming water issues.

Hard Water

Hard water is caused by excess dissolved minerals in the water. Most commonly, these minerals are calcium, lime, and magnesium. It can irritate sensitive skin and leave streaks on your clean dishes.

There is an ongoing debate regarding whether drinking hard water is detrimental to your health, but it’s definitely not good for your water supply. One look at a clogged shower head can show the effects.


Just about any appliance or amenity in your home that deals with running water will suffer from potential scale buildup. Scale is the buildup of lime or calcium, and even a small amount can drastically reduce the efficiency of your water heater.

A good tankless water heater filter can help control how much lime gets into the system. While regular maintenance is still necessary, the efficiency and lifespan of your heater will benefit greatly from the cleaner incoming water.

See Also: How to Descale a Tankless Water Heater


This is the gunk that can ruin a water heater over time. Sediment will build up from a municipal water source, but is far more prevalent with well water. It can appear as a sandy substance in the bottom of a tank and its weight means hot water tanks naturally filter out this debris through basic gravity.

Unfortunately, tankless heaters don’t store water, so sediment passes through as water’s drawn. This can lead to a number of problems, including harder water, damage to the heater, and potential clogs in your drains. While having cloudy water out of the tap is often harmless, if it’s sediment, you probably don’t want to be drinking it.

Filter Installation and Maintenance

inline tankless water heater filter

The best thing you can do to protect your tankless heater is to add a filter. The process isn’t difficult, and the cost will more than pay for itself over time by reducing the amount of damage your heater faces. Some issues may still occur, but these can be solved during regular maintenance. Keep in mind, you will also still need to occasionally flush a tankless heater.

Choosing a Good Filter

There are a couple different filter options, so you will want to focus on one that removes sediment. Cartridge-style filters tend to work the best, but you will need to make sure filter replacement is part of your maintenance routine. Smaller inline filters can be installed right before a tankless heater, while whole house water filters are designed to remove sediment as it enters the house.

Filters have one of three ratings based on rejection ratio.

  1. Absolute filters have the best filtration of the three and are best for homes where the risk of bacteria is highest.
  2. Nominal filters, meanwhile, ensure the largest particles are removed and are at least 85 percent efficient. Note that the micron number of these filters indicates the minimum particle size that will be filtered out.
  3. Beta Ratio filters require precise planning and are thus not recommended.

There are also three filtration types.

  1. Depth filters use cartridges that must be replaced over time but can catch a wide range of particle sizes.
  2. Surface filters, meanwhile, have reusable filters that use a pleated design to create more area than depth filters, making them more desirable in many cases.
  3. Absorptive filters are a more modern variant of the other two filters which can also capture negatively charged particles and microbes smaller than the micron rating of the filter.

How to Install a Whole House Filter

how to install whole house water filter
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We highly suggest getting a whole house filter, which will also filter cold water. These are generally installed against the side of the house by the cold water line’s entry point. Be sure the water supply is cut off at the meter before beginning.

  1. Attach a plywood panel to the wall near the entry point and fasten the filter’s mounting bracket to this using some hex head screws.
  2. Wrap the outlet fitting’s threads with teflon tape and tighten it to the outlet side of the filter. Add an adapter to the inlet side.
  3. Add teflon to a threaded fitting and tighten this into the adapter with a pipe wrench and pliers.
  4. Cut through the cold water pipes using a hacksaw and clean the edges with emery cloth.
  5. Mount your filter housing to the wall bracket.
  6. Push the solderless coupling onto the end of the water pipe and the valve assembly onto that. Attach this to the inlet side of your filter.
  7. Attach the second valve assembly to the outlet side and check to ensure both valves are in the off position.
  8. Attach a bare copper grounding wire between the house side of the filter to the water meter side to ensure the connection is grounded, then turn the whole unit on and test for leaks.

Additional instructions can be found here.

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases. When it comes to dealing with clogged drains, many homeowners turn