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Section 6 - System Installation
EXISTING FORCED AIR INSTALLATION
When the Maxim is installed in conjunction with an
existing forced air system, a water-to-air heat exchanger
is mounted in the plenum or duct work of the existing
furnace. Heated water from the outdoor furnace either
continuously flows through the water-to-air heat
exchanger or is diverted through a 3-way zone valve.
When the thermostat senses the need for heat, the fan
on the existing furnace forces air through the heat
exchanger, transferring heat throughout the existing
ductwork.
Following are several important items for this type of
installation.
• Plenums installed to the furnace must be
constructed of metal in accordance with NFPA
90B, 2-1.3.
• If an air conditioning coil is located in the plenum,
the heat exchanger should be mounted between
the fan and the air conditioning coil so the heat
exchanger will not freeze when the air conditioner
is being used.
• The heat exchanger should not be installed in the
cold-air return of the existing forced air furnace
because components of the existing furnace could
overheat.
• The heat exchanger may be mounted either
horizontally or vertically with the outlets on the
side (see Fig. 31).
Fig. 31
Proper Heat Exchanger Mounting
in Forced Air Furnace
Supply
Supply
Return
Return
• In all applications, the heat exchanger must be
mounted level from front to back, with the outlets
on the side. If the outlets are positioned upward or
if the exchanger is not level, an air lock can restrict
the water circulation and reduce the amount of
heat transfer.
• The lower fitting is the inlet/hot supply from the
outdoor furnace and the top fitting is the outlet/
return back to the outdoor furnace.
• It is best to install a heat exchanger that fits the
plenum.
• If the plenum is larger than the heat exchanger, it
should be mounted in the center without gaps on
the sides that would allow air to flow around the
heat exchanger. All air must be directed through
the face of the exchanger. Air flow deflectors need
to be installed in the plenum on the outlet side of
the heat exchanger if air flow is funneled into the
heat exchanger.
• Be sure to consider the airflow through the
ductwork so air circulation is not blocked off to
parts of the building.
• Adding a heat exchanger coil in the hot air
plenum or ductwork of the existing furnace may
decrease the air flow in the system. The existing
heat emitter(s) (gas or electric) should be operated
before adding the heat exchanger.
• The air temperature rise should be measured with
the heat emitter(s) running for an adequate amount
of time to get a stabilized temperature reading.
The heat exchanger can then be installed in the
system. The existing heat emitter(s) should be
operated again and the air flow should be adjusted
to maintain the same temperature reading. The air
flow may have to be increased to accomplish this.
• On a belt-drive system, the blower pulley and/
or motor pulley may be changed; however, the
electrical current flowing through the motor must
not be changed to exceed the nameplate rating.
A larger blower motor may be used. On a direct-
drive system, in most cases the blower motor will
not need to be replaced; however, the speed of the
blower motor may have to be increased.
CAUTION
When installing the heat exchanger, be sure
none of the existing system safety controls are
disabled.
NOTE: Any electrical installation should be done
by a certified electrician in accordance with all
applicable codes.
• Due to the internal circuitry of some thermostats,
a snap disc temperature control may have to be
installed on the heat exchanger manifold to provide
an interlock for the air conditioner. This prevents
the air conditioner from operating when the water
temperature is higher than 140°F (60˚C).
