Hard water and water heaters

What happens inside a tank heater

When hard water is heated, calcium carbonate comes out of it and forms solid deposits. The U.S. Geological Survey says that scale can shorten the life of equipment, raise heating costs and clog pipes. In a tank heater the deposits settle as sediment on the bottom of the tank.

Rheem says sediment build-up can reduce efficiency, raise energy bills, cause noise and shorten the life of the system. Its advice is to flush once a year for most homes and every six months if you have hard water. A.O. Smith's use and care guide gives the same six months, and Bradford White's manual tells owners to drain a gallon off monthly to clear silt and sediment.

What happens inside a tankless heater

A tankless heater heats water as it flows, through a heat exchanger. Scale forms on those heating surfaces, and DOE's lab report says scaling has a significant impact on the efficiency of tankless equipment. That is why tankless makers print water-quality limits:

• Noritz says its warranty becomes null and void if hardness above 12 grains per gallon is a contributing factor to a failure.
• Navien puts the same 12 grains per gallon as the maximum in its installation manual, lists treatment as required above it, and says damage caused by poor water quality is not covered.
• Rinnai lists scale build-up as an example of improper maintenance in its warranty, and excludes damage caused by poor water quality.

Several of the agencies on the hard water by city page publish hardness above that 12 grains per gallon line. Check yours.

What the warranties say, and what they don't

Warranties differ, and the safe summary is narrow. Some manufacturers' warranties exclude scale damage.

• Bradford White's current residential warranty excludes leakage or malfunction caused by sediment or lime precipitate in the glass-lined tank.
• A.O. Smith's residential warranty excludes failure of the water heater or its parts due to sediment build-up, and one form also excludes water that does not meet the water-quality requirements in the manual.
• Rheem's tank warranty does not use the words scale, lime or hard water. It does require operation and maintenance in line with the manual, and the manual says to drain deposits from the tank.

None of this says hard water voids a warranty on its own. A failure that has nothing to do with scale is a separate question.

What helps

• Do the maintenance in your manual. Flush a tank on the schedule your maker gives. Descale a tankless unit when the manual says to. Tank and tankless makers all publish these steps.
• Check the temperature setting. DOE's lab report found that scale builds up far faster at a 140 degree setting than at 120 degrees. In its model, at one moderate hardness level, a thin coating took about 4 years to form at 140 and almost 30 years at 120. That is a model, not a measurement of your home, and the right setting depends on your household. It costs nothing to check.
• Treat the water going in. A salt-free scale system slows how fast scale forms. A softener removes the hardness minerals, where your city allows one. See salt-free water conditioners, tankless water heater scale protection and water softeners and conditioners.

What it costs to replace one

Published price pages from Orange County and California plumbing contractors put a 50-gallon gas tank heater at roughly $2,200 to $3,200 installed and a gas tankless heater at roughly $4,500 to $7,500 installed, including permits and code work. The ranges overlap across three contractors, and they move over time. Treat them as a ballpark and get a quote.

What this does not do

• Treatment does not replace maintenance. A scale system lowers how fast scale forms. It is not a promise of a scale-free heater, and your manual's maintenance steps still apply.
• It does not guarantee your warranty. What counts is what your heater's maker accepts as water treatment. Ask the maker before you buy a treatment system, ours or anyone's.
• Softening is not a free win for a tank. DOE's lab report calls softening generally not recommended for electric tank heaters, and a last resort for gas tank heaters unless the hard water has cosmetic effects you want gone. It also quotes a heater maker's manual saying artificially softened water can be more corrosive to a tank and may shorten its life. Bradford White's manual says water conditions in your area change how often the anode rod needs checking. For tankless units, DOE's view is the opposite: softening may be required in most hard water conditions.
• It does not fix spots on glass. That takes removing the hardness. See hard water spots on glass and fixtures.

Start with the free water analysis

Know your numbers before you choose anything. The free water analysis is done at your tap. It looks at hardness, chlorine and total dissolved solids, and it is not a health screening. You see your hardness first, then you hear which options fit your water heater and your address.