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Evaluating Water

The coldest water inlet temperature experienced during the year should be the base from which
the maximum system temperature rise is established. Your water supplier can provide this
information. Surface water sources such as lakes and rivers tend to fluctuate as the seasons
change. Well water remains relatively constant in temperature year round. A water heating
system supplied with varying incoming water temperatures will only provide adequate hot water if
the lowest cold water temperature encountered is used in the temperature rise calculation.

Other characteristics of the water supply which should be determined and evaluated by the system
designer include supply pressure, water hardness and the presence of silt. These facts may be
obtained by contacting your water supplier.

High water supply pressure (above the rated working pressure of the heater) should be reduced
by a water pressure reducing valve set to about 50 psig. This will also reduce water consumption
but, more important, will bring the water pressure well within the working pressure range of the
heater. It is then possible to provide proper relief valve protection on the heater.

It is also necessary to provide water pressure reducing valves on the 180°F rinse lines of
dishwashers.

Hardness is the term applied to the compounds of calcium and magnesium present in hard
water. So common are these two minerals in water that practically no supply can be found that
does not contain at least 1 or 2 grains per gallon. Hardness is also stated in parts per million.
One grain of hardness is equal to 17.1 parts per million. Water containing less than 1 grain per
gallon of dissolved calcium and magnesium hardness minerals is considered soft water.

The significance of hardness is that the heat transfer surfaces of the water heater will become
coated or blocked with the mineral deposits. Depending upon the type of heater, less hot water,
noisy operation, increased energy costs and premature equipment failure are some of the
problems which may result from “hard” water. The system designer should select water heating
equipment which is capable of being delimed or repaired when used in hard water areas.

If the water supply contains silt or sediment, the water heating equipment should be capable of
being flushed (and have sediment risers installed in horizontal storage tanks) to extend heater
life and minimize energy expense.

The effects of hard water and silt upon the heating equipment can be minimized by lowering
water temperature, controlling flow, leakage and waste. For example, fixture and shower head
flow controls are a must to minimize hot water consumption and regulate the flow to system
design.

Energy saving fixtures benefit the user by reducing water and sewerage charges, energy and
maintenance costs. Reducing consumption through flow control is the one way initial cost,
operating costs and the space to be occupied by a new water heating system can be dramatically
reduced.

SUPPLY WATER

TEMPERATURE

PRESSURE
HARDNESS