State Water Heater Water Heater Brochure

Hard Water and Tankless Heaters
Hard water can adversely affect plumbing systems, from water piping to water fixtures and even down to the water
heating system. For piping and fixtures, hard water can create more pressure loss and reduce water flow. For water
heaters, it can even reduce energy efficiency and damage the heater. This is especially true for tankless water heaters
and it is important to understand what hard water is, what hard water does, and how to protect your tankless water
heater from possible damage caused by hard water.
What is hard water and hard water scale?
Very simply, hard water is defined as water that has a high mineral content, specifically in magnesium and calcium
(Ca
2+
and Mg
2+
ions). Hard water is not considered a health risk and these minerals generally remain dissolved in the
water. However, the problems arise when the minerals precipitate out of the water and leave behind a solid mineral
buildup. This buildup is called hard water scale, and it is this scale that reduces water flow through pipes and fixtures,
reduces the energy efficiency of water heating equipment and, at worst, causes irreversible damage to the heat
exchangers within tankless water heaters. It is important to note that the likelihood of scale formation is only based
on the hardness levels of the water and the temperature of the water, not on the material the scale is adhering to. For
example, hard water scale would form equally on a copper surface as it would on a stainless steel surface, given the
same hardness level and temperature of water.
What does hard water scale do to my water
heater?
When hard water scale forms a layer coating on the inside wall of a
tankless heat exchanger fin pipe, it acts as a thermal insulator. This
insulation effectively prevents a significant amount of heat from the
burners to properly transfer into the water within the piping. Because
the heat is not transferring into the water, the heat exchanger
material is forced to retain this excess heat, eventually overheating
and becoming damaged. Once the material has degraded enough,
the heat exchanger piping eventually gives way and water leakage
occurs.
Picture shows a clean
HX with treatment.
Scale buildup from
untreated water.
With Treatment
Without Treatment
Copper Fin
Copper Fin
Burner
Full heat transfer
Limited heat transfer
Copper Tube
Copper Tube
Full water flow and heat transfer
Limited water flow
Classification
mg/L or ppm
(parts per million)
gpg (grains
per gallon)
Soft 0 - 17 0 - 1
Slightly Hard 17 - 60 1 - 3.5
Moderately Hard 61 - 120 3.5 - 7.0
Hard 121 - 180 7.0 - 10.5
Very Hard 180 and above 10.5 and above
How is the hardness of water
measured?
Water hardness is measured in either parts per
million (ppm) or grains per gallon (gpg). Anything
that measures above 3 gpg is generally considered
hard (United States Geological Survey) and it is
advised at this point to look into water treatment.
The U.S. Department of Interior and the Water
Quality Association have classified water hardness
under several levels:
65