Tankless water heater scale protection

Why tankless heaters scale up

A tankless heater heats water as it flows, through a heat exchanger. 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. DOE's lab report on water heater scaling says scale has a significant impact on the efficiency of tankless equipment.

Several of the agencies on the hard water by city page publish hardness above 12 grains per gallon, which is the limit the tankless makers print.

What the makers' documents say

• Noritz says its warranty becomes null and void if hardness above 12 grains per gallon is a contributing factor to a failure.
• Navien gives 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 and excludes damage caused by poor water quality.

That is narrower than "hard water voids your warranty", and it is worth reading precisely. Scale damage is excluded. A failed circuit board is a different matter.

Descaling

Tankless makers expect the heat exchanger to be descaled. Rheem says tankless heaters need periodic descaling rather than flushing, and Navien's manual describes a yearly flush for residential use at moderate to very hard water levels, done with white vinegar or a solution made for tankless heaters. The right interval for your unit is in your manual. A published price page from one Orange County contractor puts a gas tankless heater at roughly $4,500 to $7,500 installed, and two other contractors publish ranges that overlap. Treat that as a ballpark for replacing one, and get a quote.

What treatment can do

The makers' tables require treatment above their hardness limits, and they list more than one way to meet it. A water softener removes the hardness minerals, where your city allows one. A salt-free scale system leaves the minerals in the water and changes how they form scale. DOE's lab report says artificial softening may be required for tankless heaters in most hard water conditions.

Treatment slows scale. It does not stop it for good, and it does not replace the descaling in your manual.

Nuvia Thermo Guard and Scale Shield

Neither of these uses salt.

• Nuvia Thermo Guard. A scale-protection system for tankless water heaters, gas or electric. One cartridge holds two stages: sediment filtration with a 5 micron rating, and a scale-reduction stage. It is listed at up to 40 gallons per minute. It is engineered to meet manufacturers' specifications for scale prevention on tankless heaters.
• Nuvia Scale Shield. A whole-home scale-prevention system with two stages, sediment filtration and a scale-control stage, listed at up to 40 gallons per minute. Its page names water heaters among the appliances it is meant to protect.

For the longer explanation of what these systems do and do not do, see salt-free water conditioners. Which one fits depends on your heater, your water and your home. A specialist works that out after your numbers are in.

What this does not do

• It does not remove hardness. The minerals stay in the water, so spots on glass and film on shower doors continue.
• It does not replace maintenance. Descale on the schedule in your heater's manual.
• It is not a warranty guarantee. The makers' tables name their own scale devices and softeners. Whether a third-party scale system meets a particular maker's requirement is something to confirm with that maker before you buy.
• It does not soften water. If you want softened water, see water softeners and conditioners for what your address allows.

Start with the free water analysis

Your hardness number is the starting point. 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 numbers, then you hear which options fit your heater and your address.