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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22108
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Have a Heat pump with auxiliary Gas Furnace one basement

Customer Question

Have a Heat pump with auxiliary Gas Furnace one basement unit with air blower and Heat pump (heat/cool) outside. My heat wire from thermostat goes straight to furnace, resulting in propane use even to heat house from 64 up to 67. I have an S1 and S2 wire going to furnace Board (same gauge as rest) which is then paired together with sensors lines (red/black) that go outside to a sensor attached to the heat pump. The white wire from the heat pump comes into the bottom of the furnace but is not attached to anything, it is just spun around the cable line coming in from outside.
Can I use the Brown (S1 sensor wire) at thermostat to connect the heat pump heat cable from outside to allow for my Next Gen3 to utilize the duel fuel system…Heat pump usage to 40 degrees then furnace takes over as auxillery?
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
This picture (132613) shows the wiring underneath the Lennox Furnace (converted to Propane at some point). The white and greren wire at the bottom right are wrapped around the harness unused. These both go outside to the heat pump and the white is connected, the green is not. The second image (115107) shows the heat pump wiring outside, white (heat) connected. The last image (133254) is the Nest thermostat. The brown and black wires (S1 and S2) for the sensor outside run to the furnace box and are the same guage as the remaining wires. Can I use the brown or the black to connect the heat pump heat (white) wire to use with the nest (* location) to utilize duel fuel heating so the heat pump will turn off and the furnace kick on at a set temperature (like 38-40 degrees or so).
Customer: replied 1 year ago.
On the same furnace wiring picture, you can see the red and black pair coming out at the bottom, that goes straight to the temp sensor outside (which is not needed on the nest). I want to disconnect those and use either the black or the brown to connect that heat pump hot (white) wire and switch nest to duel fuel. Hope that all makes sense.
Customer: replied 1 year ago.
Better pictures for review :)
Expert:  BillyHvac replied 1 year ago.

hello,

dont you have a preexisting changeover thermostat outside?