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Domestic Hot Water
When designing the water piping system for domestic
hot water applications, water hardness should be con-
sidered. Table G indicates the suggested flow rates for
soft, medium and hard water. Water hardness is ex-
pressed in grains per gallon.
Potable Water and Space Heating
1. All piping materials and components connected to
the water heater for the space heating application
shall be suitable for use with potable water.
2. Toxic chemicals, such as used for boiler treatment,
shall not be introduced into the potable water used
for space heating.
3. If the heater will be used to supply potable water,
it shall not be connected to any heating system or
components previously used with a non-potable
water heating appliance.
4. When the system requires water for space heating
at temperatures higher than 140°F (60°C), a
means such as a mixing valve shall be installed to
temper the water in order to reduce scald hazard
potential.
Pool Heating
When a boiler or water heater is used in a pool heat-
ing application, ensure that all the following installation
requirements are met.
The MVB must be equipped with a field-supplied ex-
ternal pump and bypass arrangement. This
arrangement blends outlet water with the inlet water to
Fig. 12: Single Domestic Hot Water Heater and Storage
Tank
CAUTION: When this heater is used for both
potable water and space heating, observe the
following to ensure proper operation.
ΔT = Temperature rise, °F
ΔP = Pressure drop through heat exchanger, ft
SHL = System head loss, ft (based on heater and tank placed no more than 5 ft apart and equivalent length of 25 ft of tubing)
gpm = Gallons per minute, flow rate
MTS = Minimum tubing size
* Must use optional cupro-nickel tubes. If over 20 grains per gallon, a water softening system must also be used.
Table G: Domestic Water Heater Flow Rate Requirements
NOTE: If local codes require a vacuum relief valve,
acquire one locally and install per valve
manufacturer’s instructions.
Model
No.
MBTUH Soft (0-4 grains per gallon) Medium (5-15 grains per gallon) Hard* (16-25 grains per gallon)
Input Output ΔT gpm ΔP MTS SHL ΔT gpm ΔP MTS SHL ΔT gpm ΔP MTS SHL
504 500 420 17 50 3.6 2 5.9 13 65 5.5 2 9.3 9 95 10.4 2 18.1
754 750 630 25 50 4.0 2 6.3 20 65 6.4 2 10.2 13 100 13.8 2 22.2
1104 1045 888 30 60 6.4 2-1/2 7.6 20 92 13.2 2-1/2 15.9 16 113 18.7 2-1/2 22.6
1504 1425 1211 30 82 12.7 2-1/2 14.9 22 113 22.3 2-1/2 26.3 22 113 22.3 2-1/2 26.3
2004 1900 1615 30 110 26.1 2-1/2 29.8 29 113 27.4 2-1/2 31.3 29 113 27.4 2-1/2 31.3