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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.
Fig. 9: 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.
NOTE: If local codes require a vacuum relief valve,
acquire one locally and install per valve
manufacturer’s instructions.
∆T = Temperature rise, °F.
∆P = 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.
CAUTION: For scale free operation with Medium water (5–15 grains per gallon of total hardness), the operating control must NOT
be set higher than 130°F. For higher than 130°F operation, or Hard water (>16 grains per gallon of total hardness), a water sof-
tener/treatment system must be utilized.
Table H: Domestic Water Heater Flow Rate Requirements
Model
No.
Soft (0–4 grains per gallon) Medium (5–15 grains per gallon)
∆T gpm ∆P MTS SHL ∆T gpm ∆P MTS SHL
300 30 19 8 1.5 10 20 28 17 1.5 20
500 30 31 7 2 8 20 47 16 2 18
850 30 53 17 2 20 20 80 40 2 46
Fig. 10: Multiple Boilers — Reverse Return,
Primary/Secondary Piping with Indirect DHW