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Installation instructions
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3.13 Space heating applications
Bosch tankless water heaters are approved for use in
combination DHW and space heating applications
(open-loop setup). These water heaters are not
approved for use in space heating only applications
(closed-loop setup). Bosch supports applications of
combination DHW and space heating in an open loop
configuration if plumbed similar to Fig. 42. Use of a
Bosch tankless water heater in a combination DHW
and space heating application will result in the product
warranty being reduced to 3 years.
Fig. 41 Pressure drop curve
Warning: If the set point temperature is
above 120°F, precautions should be
taken to protect users of potable water
from scalding.
Warning: Propylene glycol may be
used for freeze prevention ONLY on the
space heating side of the heat
exchanger. Do not use ethylene glycol
(automotive antifreeze).
Warning: The use of a flow switch is
recommended to ensure DHW priority
and to prevent “cold-blow” situations
when the Bosch tankless water heater is
used with an air-handling system. The
flow switch should be used to disable
the blower on the air-handling system
when domestic water is used.
Warning: Ensure the primary pump is
properly sized to provide adequate flow
for the system heat load.
For Pump sizing please refer to the
pressure drop curves, Fig. 41. Also
remember to account for system piping
pressure loss. A minimum of 1.7 GPM is
recommended to provide adequate flow
through the water heater when
determining the size of the primary pump.
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