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Section 6 - System Installation
Pressurized Water System Installations
Water-to-Water Heat Transfer System
To keep the existing system pressurized, a plate
exchanger or tube & shell water-to-water heat exchanger
installed in the return line of the existing system may be
used (see Fig. 37 and 38). The water from the existing
system passes through the heat exchanger when the
thermostat calls for heat. The water from the outdoor
furnace circulates through the other side of the heat
exchanger continuously.
It may be necessary to lower the water temperature
at which the burner in the existing boiler starts to a
setting that prevents the burner in the existing boiler
from cycling on when the outdoor furnace is heating
the home. Another option is to install a thermostatically
controlled interlock switch that prevents the burner
in the existing boiler from operating when the water
temperature in the outdoor furnace is above 150˚F
(66˚C).
Water-to-water heat exchangers will produce transfer
temperatures approximately 20ºF (11˚C) less than the
outdoor furnace water temperature; therefore if the
outdoor furnace water temperature is 185°F (85˚C),
it will produce approximately 165°F (74˚C) of water
temperature transfer. The temperature controller on the
outdoor furnace may be adjusted to allow the outdoor
furnace to reach water temperatures up to 195ºF (91˚C).
Each system will vary in water temperature transfer
depending upon the heat load of the existing heating
system.
The addition of a wraparound pump with a water-
to-water heat exchanger (see Fig. 37) may increase
heat transfer by allowing circulation continuously
through the existing boiler and heat exchanger. This
will maintain the maximum temperature in the heat
exchanger for heat transfer to the existing boiler. Note
the water flows in opposite directions through the heat
exchanger.
With this type of installation, the exchange temperature
may be more than 165°F (74˚C) and may eliminate the
need for additional baseboard heaters, panel radiators
or heat exchangers.
When installing water-to-water heat exchangers, be
sure to flush any rust particles or sediments out of the
existing boiler and install a Y-strainer as illustrated
in Fig. 37. Also be sure to add MolyArmor 350 (p/n
2900630).
A Taco 007 or 014 pump can be used as a wraparound
pump when a plate exchanger is installed. A Taco 009
or 014 pump should be used when a shell and tube heat
exchanger (i.e., p/n 148, 151 or 177) is installed.
NOTE: See the Hydronic Component Selection
Guide for more detailed information.
Existing
Boiler
Return
Circulation
Pump
Hot
Supply
1" PEX
Hot
Supply
Optional
Valves
Y-Strainer
Wraparound Pump
runs continuously circulating through the
water-to-water heat exchanger maintaining
the water temperature in the existing boiler.
This horizontal assembly
must not exceed a height
of 4 inches above top
of water heater.
For illustration purposes
only, water heater styles
may vary.
Water-to-Water
Heat Exchanger
Thermostatic
Mixing Valve
A pump must be installed in
the hot supply line between
the outdoor furnace and
thermostatic valve.
Hot Supply from Pump
on Outdoor Furnace
Return to
Outdoor Furnace
Optional
Thermostatic
Valve
NOTE
Outdoor furnace water
temperature setpoint should
be set at 185˚F minimum.
NOTE
Installer must comply with all applicable
codes and regulations.
(with Wraparound Pump)
Existing Boiler - Pressurized
Fig. 37
