Installation Manual

whl-007 Rev. 1.14.15
5
Figure 2 - Specications and Dimensions
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of relative water hardness. Grains per gallon is the common
reference used in the US water heater industry. Hardness
expressed as mg/L or ppm may be divided by 17.1 to convert
to grains per gallon. Water may be classied as very soft,
slightly hard, moderately hard, or hard based on its hardness
number. The minerals in the water precipitate out as the water
is heated and cause accelerated lime scale accumulation on
a heat transfer surface. This lime scale build-up may result in
premature failure of the water heater. Operating temperatures
above 135
o
F will further accelerate the build-up of lime scale
and may shorten the service life of the water heater.
Water that is classied as hard and very hard must be softened to
avoid water heater failure.
CLASSIFICATION MG/L OR PPM GRAINS/GAL
Soft 0 - 17.1 0 - 1
Slightly Hard 17.1 - 60 1 - 3.5
Moderately Hard 60 - 120 3.5 - 7
Hard 120 - 180 7 - 10.5
Very Hard 180 and over 10.5 and over