5 Things You Need to Know About Buying a Water Heater Filter

A water heater filter protects your water heater, as well as your pipes, fixtures, plumbing connections, and water-using appliances that are supplied by your water heater. Hard water, sediment, and scale destroy traditional and tankless water heaters. These minerals and debris accumulate on the heating element, which decreases heating efficiency and leads to premature water heater failure.

Water heater filter systems should filter out sediment and use a special blend to loosen existing scale and prevent scale from forming (anti-scale). In this article, water heater filter expert Tony Special shares advice on the most important things to keep in mind when picking a water heater filter system. Tony has over 30 years of experience producing water heater filter systems, which are the most recommended in the industry by water heater manufacturers.

What is a water heater?

A water heater is an appliance that produces a continual supply of hot water at a preset temperature. They may also be called hot water heaters, hot water tanks, boilers, or heat exchangers. A water heater can be used in domestic and industrial applications to heat potable or non-potable water.

A water heater may have a tank or be tankless. As their names suggest, hot water tanks store hot water, while a tankless water heater produces hot water on demand without storing water. Hot water heaters with a tank use a reasonable amount of electricity or gas to preheat the water stored in their tanks. Such water heaters also use a large amount of energy to keep that water warm until it is used.

Tankless water heaters are more environmentally friendly because they use a lot less energy than tank water heaters. Tankless water heaters heat water when you need it (on-demand). Essentially, when you turn on the hot side of your faucet or plumbing fixture, the tankless water heater delivers hot water. By switching to a tankless water heater, you can save 21% to 43% on your water heating costs annually.

5 Things You Need to Know About Buying a Water Heater Filter

#1: You need a water heater filter.

"An effective water heater filter is essential for all water heaters. Whether you have a tankless water heater or one with a tank, you need a water filter if you have any water hardness or sediment in your incoming water. It's just not worth risking your water heater."

The first "given" about water heater filters is that if you have a water heater, you need a good filter. A good filter system and replacement filters don’t have to be expensive, just ensure they are effective at addressing the problem at its core.

What is a water heater filter system?

The purpose of a water heater filter is to protect your water heater. Tankless and traditional water heater units are easily damaged by scale and particulates in the water. A good water heater filter system:

• Extends the life of your water heater
• Helps avoid additional maintenance and costly repairs or system replacement
• Ensures your water heater works as efficiently as possible
• Helps keep operating costs lower in the short and long run

What are water heater filters used for?

Water heater filters protect your water heater by removing particulate matter and preventing minerals that cause scale and corrosion from attaching to surfaces. Unfiltered water contains minerals and particulate matter like sediment, dirt, or rust, which can clog your water heater, form scale, and reduce its efficiency until it fails.

With a water heater filter, you can have peace of mind knowing that your water heater is protected from scale, corrosion, and particulate matter. This helps extend the life of your water heater, avoid costly repairs, and ensure that your water heater operates efficiently.

How does a water heater filter work?

A water heater filter inhibits or stops scale formation by retaining hardness minerals so they don’t accumulate on heating elements or the bottom of the water heater. In a tankless water heater, the scale inhibitor product prevents scale from accumulating on internal surfaces.

Siliphos scale control product is one of the best on the market. It takes a two-fold approach to preventing scale and corrosion in water heaters. It forms a thin protective layer on metal surfaces to prevent scale and corrosion deposits, and it also helps loosen existing scale deposits. Be sure your water heater filter contains Siliphos scale control product.

A water heater filter should also remove or reduce debris from entering your water heater.

#2: Make sure a water heater filter removes sediment, tackles existing scale deposits, and stops new scale formation.

Not all water heater filters are created equal, so ensure that your filter system accomplishes three important things:

1. Removes sediment, dirt, rust, and other particulate matter commonly found in incoming water supplies.
2. Loosens existing scale deposits on your water heater. Ideally, a filter should be installed with a new water heater, but if not, install one as soon as possible.
3. Stops new scale from forming. Some anti-scale products form a thin protective layer on metal surfaces to inhibit scale and corrosion deposits.

Be aware that many water heater filters do not remove sediment, dirt, rust, or other particulates from the water. Any "filter" that does not remove particulates should not be called a filter, but many manufacturers get away with it.

What causes scale in a water heater?

Hard water. Hard water contains minerals like calcium and magnesium, which are more likely to precipitate in hot environments like water heaters. When water is heated, minerals rapidly attach to heating elements and other surfaces. Water heaters with scale deposits are less efficient because the scale absorbs heat before it warms the water. Scale also clogs the pathways inside the water heater, leading to eventual failure.

What causes sediment to build up in a water heater?

If your water supply has debris and you don’t have a filter, this debris will get into your water heater. Sediment, dirt, rust, and other particulates accumulate at the bottom of your water heater but can end up in other areas as well. Debris also damages fixtures and appliances such as showerheads and dishwashers.

If you have a lot of debris in your water, it is highly recommended to install a point-of-entry filter (also known as a whole house water filter) to capture the debris before it enters your water heater filter and heater.

Even if you have a point-of-entry filter, it’s still recommended to have a water heater filter to provide anti-scale protection and catch any remaining sediment. From time to time, you should turn off your water supply and drain the water heater to remove as much debris as possible. Water heaters have a drain at the bottom for this purpose.

#3: A stainless steel filter housing is best.

Stainless steel water heater filter housings are superior to plastic ones. They resist corrosion and chemicals, are less likely to leak or burst, and have a longer lifespan overall. However, they are more expensive.

If you buy a plastic housing, make sure it’s manufactured from a single casting mold and that no holes were drilled after the original casting. If holes are drilled later, the filter head can be weakened, leading to leaks or bursts. In some cases, a simple bump or impact could cause an instant leak. Avoid housings with drilled holes and ask the manufacturer if the housing is from a single mold.

If you choose a plastic housing, ensure it’s made from a single mold without drilled holes.

#4: For home water heater filter systems, skip the water pressure gauge.

Water pressure gauges are designed to measure pressure drops, which usually indicate when it’s time to replace the filter. However, in residential water heater filters, gauges are inaccurate because of the low and inconsistent water volumes. They may give false readings, either prompting an unnecessary filter change or failing to indicate when a replacement is needed.

A gauge is useful for high-volume commercial applications but unnecessary for residential systems. Avoid systems with a gauge to save money and reduce the risk of misleading readings.

When do you need to replace the water heater filter?

Most filters should be changed once a year. The best way to determine when to change the filter is by marking the calendar and performing visual checks every six months. Turn the filter upside down and listen for the Siliphos balls inside. These balls dissolve over time, and once they are gone, it’s time to replace the filter.

The filter life depends on water usage and the hardness of your water supply.

#5: Template Assisted Crystallization (TAC) filters are flawed.

"Template Assisted Crystallization (TAC) filters are effective at reducing scale, but they have significant drawbacks. TAC filters have low flow rates that may not keep up with tankless water heaters. They are also easily damaged by chlorine."

Template Assisted Crystallization (TAC) technology transforms calcium ions into calcium crystals, which are easily rinsed away by the water flow. While this sounds beneficial, TAC filters have significant weaknesses.

TAC filters have low flow rates, chlorine ruins them, and it's difficult to know when to replace them.

Most municipal water supplies use chlorine, which will destroy a TAC filter unless the chlorine is removed before it passes through. Additionally, TAC filters have very low flow rates, which can reduce the performance of tankless water heaters. Sellers often provide poor guidelines for when TAC filters need to be replaced, making it difficult to determine when the media is exhausted.

Water Heater Filter Recommendations

Check out our full range of water heater filter systems and replacement cartridges.

Plastic housing: Premiere AMF-20S – 20″ Water Heater Filter System, 16 GPM flow rate

Premium 20-inch water filter housing and AMF-SDR520 scale inhibitor cartridge. This system removes sediment and protects the heat exchanger in your tankless water heater from scale and corrosion to avoid failure. Ideal for large-capacity filtration needs, including high-flow and heavy-sediment applications. Designed for all commercial and residential water heaters, including Bosch, Navien, Noritz, Paloma, Raypak, Rheem, Rinnai, Stiebel Eltron, Takagi, and more.

The filter housing is made from a single mold casting with 15% more material. It has a 5-micron deep-grooved water filter cartridge with scale inhibitor, helping protect your heat exchanger and avoid tank failure. The grooved design increases surface area, extends the cartridge life, and improves filtration efficiency. The system includes a built-in pressure release valve (PRV) to release pressure before changing filters.

Stainless steel housing: Premiere SS210-TWH - 20" Water Heater Filter System, 16 GPM flow rate

316L stainless steel housing is highly durable and resilient to corrosive substances and chemicals. It comes with a 10-year warranty. This system will not burst or fail like plastic housings. It includes the AMF-SDR520 scale inhibitor cartridge, a premium 5-micron water filter cartridge with Siliphos scale control product.

The Siliphos product forms a thin protective layer on metal surfaces to inhibit scale and corrosion. The filter cartridge has rigid construction with 68 deep grooves, increasing surface area and enhancing contaminant holding capacity. It promotes fuller utilization of the depth-matrix for fewer cartridge changes.

The system also has 3/4" or 1" FPT connections that assist in maintaining maximum flow rate with minimum pressure drop. It provides an unrestricted water flow of up to 16 gallons per minute, which meets the water pressure demands of a tankless water heater. A drain opening at the bottom of the housing allows for easy flushing and cleaning.