Is hard water bad for tankless water heaters?

Author: Grayce Goyette  |  Last update: Thursday, June 26, 2025

Scale buildup can reduce the efficiency — and even shorten the lifespan — of many items in a home. Tankless water heaters are particularly sensitive to hard water, but so are dishwashers, ice-makers and washing machines.

Will hard water hurt a tankless water heater?

Hard water contains high levels of minerals, specifically calcium and magnesium. When this water is heated in an instant or tankless water heater, these minerals can precipitate out and form scale or sediment. Over time, this sediment builds up inside the unit, reducing its efficiency and potentially causing damage.

How do you maintain a tankless water heater with hard water?

Flush to remove hard water deposits

Your tankless water heater should be flushed at least annually. This is to remove mineral deposits, such as calcium. If you've had hard water problems in your home, you might consider flushing out your heater more than once per year to counter mineral deposits.

How do I protect my tankless water heater from hard water?

Install a Water Softener: This is one of the most effective ways to prevent sediment buildup. Water softeners remove the minerals from the water before it enters the heater, thus preventing the formation of scale.

Do tankless water heaters need water softeners?

If you plan to transition to a tankless water heater in the near future, or you already have, investing in a water softener alongside it could make a huge impact. Yes, a tankless water heater can function effectively without a water softener but allowing them to work in tandem will prove worth it over time.

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How often should I flush my tankless water heater if I have a water softener?

If you have hard water, it is important to descale and flush your unit at least once a year. If you have a water softening system, we recommend performing a flush of the system every 3-5 years.

Do you need a water softener if you have hard water?

If your water's hardness is greater than 7 grains per gallon or 120 mg/L, then you might need a water softener to ensure your appliances run well and to improve the taste, smell, or look of your water.

Does hard water ruin water heaters?

Calcium buildup in a water heater is a common issue caused by hard water. This issue can lead to decreased water heater efficiency, higher energy bills and expensive damage.

Why does my tankless water heater turn blue when I flush with vinegar?

The vinegar will be a bit blue. This is from tiny amounts of corrosion of the copper of the tubes in heater. The copper imparts the blue color. Nothing to worry about.

What builds up in a tankless water heater?

Mineral buildup in tankless water heaters primarily occurs due to the high mineral content in hard water, which accumulates calcium and magnesium deposits within the system. When hard water flows through your tankless water heater, it carries these minerals that can eventually precipitate and form scale.

What is the life expectancy of a tankless water heater?

One of the most common questions asked by consumers about tankless water heaters is how long they will last. A tankless water heater can last anywhere from 15 to 20 years with proper maintenance and operation. In comparison, a standard tank water heater normally has a working life of 10 years or less.

What happens if you don't flush your tankless water heater?

As water flows through your tankless water heater, it will leave behind small amounts of minerals and sediment. Over time, this can create buildup within the unit that may negatively impact the heat exchanger and restrict water flow.

Does a water softener damage a hot water heater?

Water softening products, however, corrode the anodes more quickly compared to hard water. If the anodes are not replaced, then the metal of your hot water tank will corrode. This is what leads to the need for an early hot water replacement.

Can you take a long shower with a tankless water heater?

With a tankless water heater, you can take a shower, use the dishwasher, and do laundry all at the same time without losing hot water.

What water filter is best for hard water?

When it comes to addressing hard water comprehensively, especially for drinking, cooking, washing clothes, showering and maintaining appliances and household pipe systems, reverse osmosis (RO) is seriously effective. Here's why undersink RO systems are the best solution.

Where should tankless water heater not be installed?

Keep your water heater away from outside elements

If your tankless heater is exposed to extremes weather conditions, it will run a greater risk of premature failure. So, make sure your appliance is away from doors and windows, and never installed in the garage or basement.

How much does it cost to descale a tankless water heater?

Flushing and descaling are important parts of that maintenance, no matter what kind of water you have. Descaling your tankless water costs between $150 and $450 on average.

What is the best chemical to flush a tankless water heater?

Use 4 gallons (15.1 liters) of undiluted white vinegar to clean your tankless water heater. Never use chemical solutions of any kind. Since your home's drinking and bathing water mostly likely flows through your tankless water heater, using chemical cleaning solutions could be extremely harmful to your health.

Is vinegar or descaler better for tankless water heaters?

A tankless water heater descaler specifically designed for this purpose is recommended for optimal results. Alternatively, you can use vinegar as a natural and affordable descaling solution. Prepare the solution according to the manufacturer's instructions.

Are tankless water heaters OK with hard water?

When hard water is heated, the minerals can precipitate out of the water and form scale deposits inside the heater's heat exchanger and other components. This buildup can reduce the heater's efficiency, impede water flow, and lead to costly repairs or premature failure.

How often should you drain your water heater with hard water?

If you live in an area with hard water (that has high mineral content), Angi recommends you may want to drain it every six months, or so.

Does hard water cause hair loss?

Hard water damages the hair fibre, causing dryness and split ends when used regularly. As a result, the hair becomes dull and brittle. This can lead to long-term hair loss.

What is the downside of a water softener?

The two major cons associated with water softeners are cost and maintenance. Depending on the type and size of water softener you choose, the initial price along with installation can cost you anywhere from a few hundred to a few thousand dollars.

Does Brita filter hard water?

BRITA water filters are specifically designed to filter water to help reduce hardness while leaving in the important minerals that are healthy for you. This is the work of the Ion Exchange Pearls, that bind metal cations like lead and copper. BRITA filters do not filter out all calcium or magnesium.

How can permanently hard water be softened?

Water softening is achieved either by adding chemicals that form insoluble precipitates or by ion exchange. On a small scale, chemicals used for softening include ammonia, borax, calcium hydroxide (slaked lime), or trisodium phosphate, usually in conjunction with sodium carbonate (soda ash).

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