Product Guide

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:
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