NS SPLIT INSTALLATION MANUAL
General Installation Information (cont.)
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 auxiliary 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.
In add-on Envision Split applications, the coil should be located in the supply side of the furnace to avoid condensation 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 on page 15 for details.
Figure 2: Typical Split System Heat Pump Coil Add-On Fossil Fuel Furnace
Disconnect | | Supply Duct |
| |
| "A" or | |
| Slab Coil | |
Insulated | | |
Suction Line | | |
| Wire To | |
| Thermostat | |
| | Condensate |
| | Drain |
| | (must be trapped) |
| | Up-Flow |
| | Fossil Fuel |
Lineset To Air Handler | Return | Furnace |
| |
| Duct | |
Thermostat | | |
Wire From Furnace | |
