Design Manual

7 R-TRWH-E-02 Rev D
Water Quality and Scale
A complete water analysis and an understanding
of system requirements are needed to protect the
Rinnai tankless water heaters and water heating
systems from scale. Water analysis shows
whether water is hard or soft. Hard water, unless
treated, will cause scaling or liming of the Rinnai
heat exchanger.
The rate of scaling increases with temperature
and usage because calcium carbonate and other
scaling compounds lose solubility (fall out of
solution) at higher temperatures. For example,
for every 20°F over 140°F, the rate of scale
increases by a factor of 2 (See figure below).
Reference target water quality levels below and
treat the water if these levels are exceeded.
* Source 2003 ASHRAE Handbook HVAC Applications
210
180
150
120
90
60
30
0
3900 3300 2700 2100 1500
900 300
0
WATER USAGE, gal/day
LIME DEPOSITED, lb/yr
180°F
170°F
160°F
150°F
140°F
120°F
BASED ON 10 grains/gal HARDNESS
*
Consideration of care for your water heater should
include evaluation of water quality.
Water that contains chemicals exceeding the
levels shown in the table affect and damage the
heat exchanger. Replacement of the heat
exchanger due to water quality damage is not
covered by the warranty.
If you live in an area that is known to have hard water
or that causes scale build-up you must treat your
water and/or flush the heat exchanger regularly.
When scale build-up in the heat exchanger begins to
affect the performance of the water heater, a
diagnostic code “LC” will display. Flush the heat
exchanger to prevent damage to it. Scale build up is
caused by hard water set at a high temperature.
Maximum Level
Total Hardness Up to 200 mg / L
Aluminum * Up to 0.2 mg / L
Chlorides * Up to 250 mg / L
Copper * Up to 1.0 mg / L
Iron * Up to 0.3 mg / L
Manganese * Up to 0.05 mg / L
pH * 6.5 to 8.5
TDS (Total Dissolved
Solids) *
Up to 500 mg / L
Zinc * Up to 5 mg / L
* Source: Part 143 National Secondary Drinking Water
Regulations