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NSZ/NDZ INSTALLATION MANUAL
Dual Fuel Systems
Envision units can be connected to fossil fuel furnaces that
include an A-coil or slab coil. Dual fuel installations utilize
the Envision heat pump for heating until the point that aux-
iliary heat is called for on the thermostat. At that point, the
furnace will be enabled and the heat pump will be disabled.
The Envision heat pump provides air conditioning through
the furnace’s refrigerant coils.
Refer to the furnace manufacturer’s installation manual
for the furnace installation, wiring and coil insertion. A
WaterFurnace Dual Fuel thermostat, a field-installed DPST
relay or dual capacity auxiliary heat relay is required. See
Figure 2 for typical Dual Fuel application.
Disconnect
Thermostat
Wire From Furnace
Vibration Absorbing Pad or Air Pad
P/T Plugs
Wire To
Thermostat
Up-Flow
Fossil Fuel
Furnace
Condensate
Drain
(must be trapped)
"A" or
Slab Coil
Supply Duct
Air Temperature Limit Switch -
to prevent compressor operation
when entering air is greater than
90°F.
Water Out
Water In
Lineset To Air Handler
Insulated
Suction Line
DHW In
Return
Duct
DHW Out
Maximum Recommended Distance
is 60' Between Units
Figure 2: Typical Split System Heat Pump Coil Add-On
Fossil Fuel Furnace
In add-on Envision Split applications, the coil should be
located in the supply side of the furnace to avoid con-
densation damage to the furnace heat exchanger. A high
temperature limit should be installed upstream of the coil
to de-energize the compressor whenever the furnace is
operating. Without this switch, the Envision Split will trip
out on high pressure. A dual fuel thermostat can remove
the Y1 and Y2 calls when a W call is energized to allow gas
furnace backup on an Envision Split application. Refer to
thermostat wiring diagram for details.
General Installation Information cont.
