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Do I Need a Tankless Water Heater Filter?

Posted by Brock Robinson on May 03, 2023

tankless water heater

Tankless water heaters have become increasingly popular for homeowners around the globe. Hyper-efficient, long-lasting, and conveniently sized, tankless water heaters greatly reduce the amount of energy consumed by your household each day. However, the lifespan and performance of a tankless water heater are dramatically affected by the quality of the incoming water. Scale, a prime enemy of all appliances, can choke the heating element and prematurely destroy the unit. Sediment build-ups can clog the system and cripple the unit’s efficiency. A tankless water heater filter preserves the lifespan of your heater by guarding the unit against mineral build-up and sediment and protecting the heater from damage. 

How does a tankless water heater work? 

Tankless water heaters heat water up directly and only when it is needed. They don’t require bulky storage tanks and use far less energy than their traditional counterparts. When you turn on your shower to step into a steaming, relaxing shower, a sensor in the tankless water heater is alerted that there is a demand for hot water. An electric heating coil or gas burner ignites, and the heat is transferred to the water circulating through the pipes in the heater. These powerful heating elements elevate the temperature of the water rapidly. 

The water then enters a mixing valve, where cold water is added to the water to regulate the water’s scalding temperature.  Upon exiting the heater, the water passes through a second sensor. This temperature sensor reads if the water is too hot (or not hot enough) and adjusts the internal elements accordingly. The water is then distributed into the home’s plumbing and exits out of your showerhead. Tankless water heaters, also known as on-demand heaters, only use energy when hot water is demanded.

Traditional tank heaters are almost constantly using energy to keep water hot and ready for usage. These heaters fill large, 40-50 gallon storage tanks up with water, then drain energy keeping the water perpetually heated. Regardless if anyone is using hot water, or if there’s even a soul in the house, energy is dumped into keeping the stored reservoir of water hot. Furthermore, conventional tank water heaters are incredibly inconvenient. If someone washes a load of dishes right after a bath is run, you have to wait for that storage tank to fill with water and then wait for it to heat up before accessing it. This can get in the way of cleaning, doing laundry, bathing, and simple household tasks (and mean settling for a cold shower if the rest of your household uses up all the hot water before you get the chance). Not only do tankless water heaters reduce energy usage, but they also produce hot water on demand. With innovations in design, some recirculating tankless water heaters even produce hot water instantly.

Advantages of a tankless water heater

  • Energy efficient: Tankless water heaters only heat up water when there is a demand for it in the household. There is no energy is expended keeping water hot in between use. These incredibly efficient unites reduce water heating energy costs of the average family around 25%-40%. If you install multiple tankless water heaters (targeting every hot water-using appliance) you can achieve over 50% reduction of energy costs. Even homes with high water consumption will see their monthly energy costs reduced. Not only do they use less energy, but they also do not waste any energy. About 50% of the energy used by traditional water heaters goes toward simply maintaining the hot water’s temperature.  
  • Compact size: Tankless water heaters are compact units, conveniently sized to fit flush against a wall, inside a cabinet, or beneath a sink. Traditional water heaters hold 50 gallons of water and can stretch 20 feet. These eyesores can take up significant room in your garage, basement, or attic. Smaller homes may even have them taking up space in a bathroom or hall closet. In contrast, tankless water heaters are flat and usually no longer than 2 or 3 feet. They can be installed inside or outside and because of their size, they fit comfortably on any wall and location of your choosing.  
  • Increased safety: Traditional water heaters are prone to leaking, bursting, and flooding, leaving costly water damage behind. Older units are prone to springing leaks, a risk that is eliminated by a tankless heater, as they don’t store any water. In the event of an earthquake, you don’t need to worry about 50 gallons of scalding water crashing down and destroying everything in the room. Since tankless water heaters don’t hold any standing water in them, there’s no risk of bacteria like Legionella accumulating inside the tank and making your household sick.   
  • Hot water on demand: With a tankless heater, there’s no waiting around for the tank to heat your water up. If you want to step into a hot bath, all you have to do is turn on the hot water faucet and fill the tub up. Regardless of how much hot water was recently used, a tankless water heater provides you with hot water when you want it and where you want it. You aren’t limited by the gallon capacity of the water heater’s storage tank. Since there is unlimited hot water available, tankless systems are ideal for filling up hot tubs and whirlpools as well. The immediacy and convenience of a tankless water heater are some of the system’s biggest draws. 
  • Versatile installation options: Tankless water heaters can be installed almost anywhere you desire. You can opt for one tankless unit that heats up water for the entire household or install multiple heaters in front of every hot water-using appliance. Traditional water storage units are massive tanks that can only be installed at the home’s point of entry. This makes plumbing water filtration around the heater more difficult, as well as limits where in the house the heater can feasibly be installed. With tankless units, you have the freedom to install them wherever suits your home best.   
  • Longevity: Most tankless water heaters have lifespans of 20 years or longer. Though more expensive initially than conventional water heaters, they pay for themselves in longevity alone and last twice as long as tank-style systems. Your typical water heater with a storage tank is only expected to last eight years to a decade, and certainly no longer than fifteen years. The extended lifespan of tankless units not only saves you energy costs over time, but it also saves you from costly installation and plumbing fees every ten years. Without filtration, water heater storage tanks can also fill with sediment or become clogged by scale, further reducing their expected service life. 
  • Wi-Fi Connectivity: One unique feature of many new tankless water heaters is Wi-Fi connectivity. These “smart tankless heaters” can remotely control the temperature of your water. If you’re getting ready to run a hot bath, you can alert your tankless heater and eliminate any waiting time. They also allow you to regulate the temperature of your heater from your phone, monitor water usage, and create a schedule for the heater to turn. If you have a recirculating tankless heater, you can use your smart heater’s app to initiate recirculation. 

Disadvantages of tankless water heaters

  • Initial price tag: Tankless water heaters are expensive. They cost significantly more than a storage tank-style heater system. However, because of their significant energy savings, tankless heaters will pay for themselves throughout the lifespan of the unit. Since these units are about 25-35% more efficient than storage tank heaters, these are actually the cheaper option long term. 
  • Cannot operate under low flow: Tankless water heaters require a flow of at least 0.5 GPM (gallons-per-minute) to operate. If the flow drops below this, the water will not heat up properly. This is part of what makes a tankless water heater filter so integral to protecting the heater’s performance. If the unit is clogged with scale, or if household plumbing and appliances are scale-ridden, the flow rate will drop and the heater will not work. By protecting it from sediment and hard water minerals, you can ensure your system remains high functioning. 
  • Power dependent: Tankless water heaters rely on electrical power to work. This means if your power goes out, so does your hot water. Here, storage water heaters do have an advantage. You can still draw from the reserve of hot water after a power outage until you use up all the heated water or the water begins to cool down. A tankless system has no means of providing hot water without an electrical connection. 

How much does a tankless water heater cost? 

A tankless water heater will cost between $1,000 and $4,000, including installation. Electric tankless heaters tend to be less expensive, costing around $1,500 on average. A gas-fired tankless water heater usually costs $3,500 to install. 

This is a higher price tag than storage tank water heaters, which usually range from $500-$800 dollars to install. However, keep in mind the longevity of a tankless heater and the significant energy savings will pay for the system over time. Storage tank systems usually last about 10 years, where a tankless system has a lifespan of 20 years. If the tankless system saves you just $100 a year, that’s an energy savings of $2,000 over its lifetime, plus the added $800 saved where you didn’t have to replace the system ten years in. Most high-efficiency tankless water heaters will save you far more than $100 per year, especially in smaller households. 

It’s also important to note these costs are including the estimated installation fees of the plumber. Installing a tankless water heater is complicated electrical work, and should not be attempted by a homeowner as a DIY installation. The skills of a professional licensed plumber are needed for this installation. 

tankless water heater filter

What’s the difference between a gas and electric tankless heater?

Electric tankless heaters are cheaper, lower maintenance, are powered by electricity and do not require extensive installation. Gas tankless heaters have significantly higher price tags than electric units, need propane or natural gas to operate, and require venting and a fresh air supply. Gas heaters will need annual maintenance inspections from licensed professionals. Since the price of natural gas is slightly cheaper than the price of electricity, the operating costs of gas heaters tend to be lower than that of electric ones. However, gas tankless heaters do produce greenhouse gas emissions during use, and the price of natural gas tends to fluctuate. Electric tankless heaters tend to boast higher efficiency (around 98% of the energy used goes directly toward heating water.) Conversely, gas heaters hover around 85% efficiency. Both units, however, are widely more efficient than their tank-style counterparts. 

Both gas and tankless heaters can claim a host of cost and energy-saving advantages compared to storage tank units. So, ultimately, the choice between a gas-powered or electric tankless heater will come down to personal preference, available space, and the homeowner’s budget. Generally speaking, electric tankless heaters are preferred. They are cheaper, more environmentally-friendly, and are far easier to install. Especially if you plan on installing multiple tankless heaters, electric units are a stronger choice. Since they release exhaust gases as part of the heating process, gas units require extensive venting and air circulation, a consideration you do not have to make if you are installing an electric heater. Electric tankless heaters do not release any exhaust, broadening your choice of installation locations. Gas units are also higher maintenance and far more difficult to service. Electric units are usually simple to troubleshoot and repair, which generally means they tend to have a longer lifespan than tankless gas heaters. 

Do I need a tankless water heater filter?

Yes, a tankless water heater filter is essential to protecting your water heater from damage by inhibiting the accumulation of scale. Scale will clog the restrict flow rate, reduce the efficiency of the heater, and over time, cause severe damage and ultimately destroy the heater. A tankless water heater filter eliminates calcium and magnesium (the minerals responsible for creating scale) from the water, preventing scale build-ups and preserving the lifespan of your heater. A tankless heater is a valuable investment. They will save you on energy costs, eliminate long waits for hot water, and last for decades if properly maintained. Letting water hardness clog the unit with scale can be detrimental and prematurely ruin your investment, or at the least incur expensive servicing. 

When scale forms along the heating elements within a water heater, the heater loses efficiency. When a demand for hot water is initiated, the heating elements are forced to heat up the calcified crust of scale in addition to the heating element, causing them to expend extraneous effort. A build-up of scale will make the transfer of heat within the heater much more difficult. The unit is forced to work twice as hard to achieve the optimal temperature range. This puts a significant strain on the heater. A scale-ridden tankless heater will overexert itself during operation. This will inevitably cause the unit to fail far sooner than its expected lifespan. Furthermore, this wasted energy runs counterintuitive to the motivation behind installing a tankless system to begin with. All your energy savings will be lost if the machine is coated in scale.

Tankless water heaters are particularly vulnerable against hard water. When the water is heated, the calcium and magnesium will emerge as scale much faster. Hot water aids in mineral content converting into a solid form. Tankless heaters and storage-tank water heaters alike are very likely to become choked by scale. Other hot water-using appliances, like dishwashers, laundry machines, and showerheads, are also prime targets for scale build-up if left undefended. 

Learn more about how water heater filters work

What is hard water? 

Hard water is water with an abundance of calcium and magnesium ions present in it. When water passes through the layers of the earth’s crust, it absorbs calcium and magnesium from rocks like gypsum and limestone. These natural minerals create “water hardness.'' Calcium and magnesium resist staying in a dissolute form and are eager to re-emerge as solid precipitate. This is precipitate is called calcium carbonate, also known by the names limescale and scale. Scale is a crusty, white build-up that clogs pipes, leaves streaks of soap stains on glass, and is notorious for destroying appliances. Hard water is one of the most common water quality issues in the United States.

Learn more about hard water.

How do tankless water heater filters work?

Tankless water heater filters remove scale-forming minerals and sediment from the water. This protects the tankless water heater from damage, corrosion, and diminished efficiency. Tankless water filter heaters use different methods to prevent scale from forming within the heater. These methods include phosphate, template-assisted crystallization, and proprietary scale control blends. An ion exchange water softener will also remove water-hardness causing minerals. 

Phosphate filters 

One of the properties of phosphate crystals (polyphosphates) is an ability to inhibit the crystallization of magnesium and calcium. Owing to this, phosphate filters are known as “scale inhibitors”. When the water flows through the filter, the phosphates attach to the calcium and magnesium ions. These “sequestered” water hardness minerals are unable to emerge out of the water, obstructing the formation of scale. 

Phosphate cartridges are depleted over time and depending upon the severity of your water hardness. The harder the water, the more phosphate will be used to isolate and neutralize the hardness minerals. Most phosphate cartridges will last between six months and a year. However, phosphate filters are generally not the first choice for a tankless water heater filter. Hot water causes phosphates to break apart, dramatically reducing their efficacy as an anti-scale agent. If you plan to use a phosphate scale inhibitor, make sure it is installed on a cold water line to see the greatest results. If hot water passes through the filter, the heat will break down the phosphate before the phosphate can sequester it. This will allow calcium and magnesium to enter into the tankless heater and form scale. 

Some carbon filters incorporate phosphates to add an antiscalant component to the filter. These are often used in restaurants and commercial beverage applications. Increased water hardness has a ruinous effect on coffee, espresso, and fountain beverages. Carbon and phosphate composite filters ensure that the mineral content of the water doesn’t undermine the flavor profile of your coffee or your refreshing carbonated drinks. 

TAC (Template-Assisted Crystallization)

One of the most popular ways to stop scale from entering into a tankless water heater is by using a template-assisted crystallization filter inline ahead of the filter. Template-assisted crystallization (also called TAC) prevents calcium and magnesium minerals from emerging from the water and creating scale. TAC filters use tiny polymer beads covered in craters called “nucleation sites”. When the hard water flows over these beads, the calcium and magnesium ions deposit on these nucleation sites. As the nucleation sites continue to collect mineral ions, they form micro-crystals out of calcium and magnesium. 

These crystals will eventually break off and flow through the heater. However, these micro-crystals are entirely stable. They will not stick to pipes or cause scale to accumulate on appliances or on heating elements. In fact, these micro-crystals actually help clear pre-existing scale formations out of your plumbing. TAC is the technology used in many whole-house salt-free water conditioners (or sometimes deceptively marketed as “salt-free water softeners”.) While they do not soften the water, they do render the hardness minerals incapable of emerging from solution to create scale. They are also popularly sold in cartridge form to be installed directly in front of tankless water heaters. 

template-assisted crystallization (TAC) graphic

TAC media can continue to isolate hardness ions and create micro-crystals for 3-5 years before requiring replacement. However, it is vital to note that the TAC beads are sensitive to chlorine. Chlorine is used by most municipal water suppliers as a water disinfectant, eliminating waterborne pathogenic bacteria. However, the chlorine will wear down the TAC media prematurely. Chlorine will monopolize the nucleation sites and micro-crystals will not form. While most city water will not have exorbitant levels of chlorine, it is recommended that all TAC filters are preceded by a carbon filter. The carbon filter will adsorb the chlorine content, which will improve both the efficiency of the TAC filter as well as the taste of your water. 

Learn the truth about salt-free water softeners. | Read more about how carbon filters work

Water softeners

If you have hard water, one of the best and most time-honored solutions is a water softener. A water softener will protect not only your tankless water heater from scale, but ensure your entire home is free from hard water damage. Your dishwasher, your laundry machine, and all your hot water fixtures will all fall victim to the scourge of hard water if it is not properly addressed. Hard water also prevents soap from lathering, dries out hair and skin, and causes streaks to form on your shower doors and kitchen countertops. If you are concerned about preserving your tankless heater, it is worth investing in a water treatment system that will protect your whole home. 

Water softeners are whole house water filtration systems that eliminate water hardness entirely. Phosphates and TAC both neutralize water hardness minerals and stops them from becoming scale. Only a water softener altogether removes the minerals from the water. Water softeners eliminate water hardness by passing hard water through a bed of polystyrene resin beads. These beads are flushed with a salt-rich brine solution, which leaves each resin bead charged with a sodium ion. When hard water passes through the column of resin beads, a process called ion exchange occurs. The calcium and magnesium ions are attracted to the positive charge of the resin beads. The beads then grab ahold of the mineral ions and release the sodium ions into the water. The water then exits the tank and flows into your home softened and mineral free. When the resin beads have taken on enough mineral ions, a regeneration cycle is initiated. This flushes the resin, sending the hardness ions to the drain and recharging the beads with sodium ions. 

Water softeners are a fantastic way to preserve not only the lifespan and performance of your tankless water heater, but they’re also a worthwhile investment for anyone living on hard water. They will protect your heater from being choked with scale, as well as eliminate the myriad of headaches that water hardness brings to a home.

Explore how water softeners work. | Read 5 benefits of having a softener

Sediment filters

A sediment filter is another valuable tankless water heater pre-filter. Tankless water heaters have a narrow inlet designed exclusively for water flow. Dirt, debris, and particulate matter will all result in the unit clogging. If sediment builds up in a tankless heater, the unit will malfunction and eventually stop working altogether. Depending on the extent of the damage, you will have to purchase replacement parts or potentially an entirely new unit. 

Tank-style water heaters are better equipped to handle sediment. Sediment will accumulate in the tank and settle at the bottom. The tank is then periodically flushed, clearing the tank of sediment. Waiting too long to flush a storage tank water heater will eventually result in leaks and diminished efficiency. However, tankless heaters have no place to store the sediment. Any internal blockage on a tankless heater will result in immediate damage to the system and a significant reduction in efficiency. If the inlet valve becomes obstructed by sediment, water will be unable to even enter the system, much less fill your tub with hot water.  

If your home relies on well water, you are the most vulnerable to sediment build-ups. Everything from sand to flecks of dirt to solid debris can make its way into your water. While sediment filters won’t reduce heavy metals or mitigate scale, they will ensure the passageway to your tankless heater remains open. Installing a whole-house spin-down sediment filter or a 5-micron pre-filter before your tankless water heater will keep it clean from debris and preserve the unit’s efficiency. 

Learn more about how sediment filters protect your home and appliances. | Explore how spin-down filters work.

Comments 1-10 of 1

Can i change the inlet water filter (I’m using glycol) with a larger one and connect it to the outgoing hot glycol or incoming piping system?

Russell S Struve on March 27, 2023
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