Expert Tips on Tankless Water Heater Filter Selection and Use

Understanding the importance of a tankless water heater filter is crucial, especially for those under the misconception that these systems don't need one due to their lack of water storage.

This guide dispels that myth, highlighting the significance of filters for homes in hard water areas or those using well supplies.

Tankless water heaterTankless water heater

Tankless water heater filter: Essential considerations for optimal performance

The purpose of a tankless water heater filter

A tankless water heater filter is a crucial component designed to purify the water entering a water heating system.

Unlike traditional water heaters with storage tanks, these on-demand systems heat water directly as it passes through the unit, making them more susceptible to damage from sediments and minerals commonly found in water.

The primary purpose of these filters is to trap and remove these impurities, such as dirt, sediment, and minerals, before they enter the heater.

This not only protects the internal components of the heater from scaling and corrosion but also ensures the efficiency and effectiveness of the heating process.

By doing so, the filter plays a vital role in maintaining the overall health and longevity of the tankless water heater system.

Types of tankless water heater filters

tankless water heater filter(photo: amazon)

When it comes to maintaining and extending the life of your tankless water heater, choosing the right type of filter is crucial. They come in various types and sizes, each designed to tackle specific issues in water quality that can affect the performance and longevity of your heater.

Note that smaller inline filters can be set up directly before a tankless heater, whereas whole-house filters are engineered to eliminate sediment as it enters the home from any source.

Sediment filters

Sediment filters for tankless water heaters are designed to capture and remove solid particles like dirt, sand, and rust from the water. They are particularly beneficial in areas with high sediment levels in the water supply.

Carbon filters

Carbon filters are another type of filter used in tankless water heaters, primarily focused on improving water quality.

While they don't directly affect the heating elements, carbon filters contribute to the overall health and safety of the water supply. They are especially valuable in urban areas where the municipal water may contain higher levels of chlorine and chemical additives.

Scale inhibitor filters

Scale inhibitor filters are specifically designed to tackle the problem of hard water minerals, such as calcium and magnesium, which can cause scaling inside the tankless water heater.

Scale inhibitors are a must-have in areas with hard water to prevent the gradual decrease in heating performance and efficiency.

Multi-stage filters

Multi-stage filters combine various filtration technologies, like sediment filtration, carbon filtration, and scale inhibition, in one unit. These comprehensive systems offer the best protection for tankless water heaters by addressing multiple water quality issues simultaneously.

Selecting tips

Choosing the right tankless water heater filter involves considering several crucial factors.

Firstly, assess your water quality to determine the specific impurities and contaminants present in your water supply.

Secondly, consider your heater model and its flow rate, as different models may require filters with varying capacities. Additionally, think about your household's water usage habits, as this can impact the frequency of filter maintenance.

Lastly, budget considerations should not be overlooked, as they come in a range of price points.

Also, the source of your water supply plays a significant role in filter selection.

If you receive water from a municipal source, it may have different quality characteristics than water from a well.

Municipal water may contain chlorine and disinfection byproducts, making carbon filters a beneficial choice.

In contrast, well water often has higher mineral content, necessitating scale inhibitor filters.

Benefits of using a tankless water heater filter

Extended heater lifespan

Using a tankless water heater filter significantly extends the lifespan of the heater.

By ensuring that only clean water flows through the system, these filters reduce wear and tear on the internal components, thereby prolonging the operational life of the heater.

This means fewer repairs and replacements, making it a cost-effective solution in the long run.

Improved water quality

Installing a filter enhances the overall quality of the water. By removing contaminants such as sediment, chlorine, and other chemicals, the filter ensures that the water is not only safe for use, but also free from unpleasant odors and tastes.

This leads to cleaner, clearer water for all household uses, ranging from cooking to bathing, and provides a more pleasant and healthy water experience.

Reduced maintenance needs

Implementing a filter in a tankless water heating system can significantly reduce maintenance needs. This means less frequent cleaning and descaling is required, saving time and reducing the costs associated with maintenance activities.

Improved energy efficiency and cost savings

Installing a filter in a water heating system contributes to greater energy efficiency and cost savings. This improved efficiency not only reduces the environmental impact but also translates to lower energy bills.

Furthermore, with the heater operating at optimal efficiency, there's less strain on the system, which can prevent costly repairs and replacements, contributing to overall cost savings.

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Signs you need a tankless water heater filter

Decreased water temperature

One of the key signs indicating the need for a tankless water heater filter is a noticeable decrease in water temperature.

When sediments and minerals build up in the heater, they can insulate the heat exchanger, reducing its efficiency.

This results in the heater struggling to reach the set water temperature, leading to lukewarm water output.

Installing a filter can prevent these impurities from entering and affecting the heater's performance, ensuring consistent hot water supply.

Reduced water flow

Reduced water flow from your fixtures can be another sign that your water heating system needs a filter.

Sediment and scale buildup in the heater can obstruct the water flow, leading to a noticeable decrease in the water pressure.

This is particularly evident during hot water usage. A filter helps in trapping these particles before they enter the heater, maintaining optimal water flow and pressure.

Unusual noises from the heater

Unusual noises emanating from your tankless device can be an indication of sediment accumulation inside the unit.

These sounds, often described as popping or crackling, occur when water interacts with the sediment deposits on the heat exchanger.

The presence of a filter can minimize the entry of these particles, thereby reducing the likelihood of such noises and maintaining the quiet operation of the heater.

Visible sediment in water

The appearance of visible sediment in your hot water is a clear sign that your tankless unit could benefit from a filter.

A filter effectively screens out these particles, ensuring that the water coming out of your heater is clean and free from visible impurities, thereby protecting both the heater and your home's plumbing system.

Can I install a water softener instead?

Yes, you can install a water softener as an alternative or complementary solution to address hard water issues in your home.

A water softener is a more expensive project but will not only supply soft water to your water heater but your whole home. The ion exchange system involves two tanks – one filled with resin beads that draw the contaminants out of the water supply and hold them, delivering clean, soft water throughout your home.

The system has a second tank where salt crystals mix with water and backflush the resin beads to remove the contaminants they have trapped. They are flushed away down your wastewater drain. The resin beads are washed again with clean water, and the job complete. The system runs automatically; all you have to do is check the salt level regularly and top up as needed.

A water softener system will deliver soft clean water to your home and will prevent all of the issues that go along with hard water and ruin your appliances.

How to address water temperature issues: What to do when it's cooler than expected

Here are four quick checks you can perform to determine the issue and take corrective measures before contacting a plumber.

Check the thermostat

Check your water heater thermostat. It may be set a bit low and could benefit from a slight adjustment upward, especially if the outside temperature has dropped. The thermostat setting that works well during warmer months may be too low to handle the colder water temperatures in winter. Coldwater temperatures can vary throughout the year, and they tend to be several degrees lower in the winter when entering your heater.

Check the water screen

Check the water screen on the cold water supply side of your heater and clean it monthly. These are easily accessed and removed for simple cleaning. The little filters catch a lot of debris and can be easily blocked, which will cause low flow into your water heater and, in turn, restrict the delivery of hot water to your faucets.

Check the plumbing

Check the pipes coming from the water heater. If the hot water supply pipe is leaking, there will be lower pressure and a reduced amount of hot water.

Check the route of the hot water supply pipe and look for visible leaks and puddles, or if you hear dripping, you need to identify where the leak is and fix it. It's essential to prevent the loss of expensive hot water.

Check for discolored water

If your hot water is discolored, there may be a buildup of residue inside the water heater on the heat exchanger, which will lower the heater's efficiency.

Check, and if you see limescale, that will prevent your water from heating. Flush the heater out with clean water and household white vinegar to clear the problem.

Regular maintenance

Regular maintenance of your tankless heater will ensure you avoid serious problems that can shorten its life and cost you more to run.

Check the water filter screen on the incoming side of your heater and clean it monthly. These little filters catch a lot of debris and can block up quickly, which will cause low water flow into your heater and restrict the delivery of hot water to your faucets.

An inline filter fitted to your water supply will prevent the small screens from blocking up every couple of weeks, especially with well water. The only maintenance it needs is every couple of months. Check and change the cartridge if it's dirty.

Check the heat exchanger, and if it appears contaminated with sediment, it needs to be cleaned and de-scaled. If it builds up, it will take the burner longer to heat your water, which will cost you more in energy and shorten the life of your heater, and they are not cheap to replace.

It would help if you flush your tankless water heater at least once a year for around an hour with water and white vinegar. All of these basic procedures will increase the lifespan of your heater. Cleaner water coming through the heater will also help it work more efficiently and save you money.

Check your pressure relief valve once a month to ensure it's working correctly. If it becomes blocked with sediment, it could stop it from functioning in an emergency, which is potentially dangerous.

It's an excellent plan to have the unit (mainly gas), professionally checked to ensure it's running efficiently; however, flushing is a job you can do yourself and save money.


Tankless water heater filters play a vital role in ensuring the longevity and efficiency of your system.

While your tankless water heater may not necessarily require a filter, we strongly recommend homeowners invest in proper filtration.

The benefits are substantial and include extended heater lifespan, improved water quality, reduced maintenance needs, enhanced energy efficiency, and cost savings in the long run.

Don't overlook the importance of quality filtration—it's an investment in the comfort, convenience, and durability of your home's hot water supply.

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