Dual fuel systems be it gas propane or oil back up heat depends on the system controlling it. If you have a "kit" for dual fuel you should be able to find the brand of kit and look it up. Newer t-stats will operate duel fuel without the kit like the vision pro from Honeywell.
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The kit usually has the sequence of operation and install instructions. Is that what you are looking for? Not all duel fuel systems work the same, some have outdoor stats or sensors, some dont. In most cases, 2nd stage will shut down the hp and fire up the fossil fuel. Some keep it on until 1st stage is satisfied, some dont.
Some will run 1 or the other, some will fire the furnace for backup. Some return to the heat pump, others keep the furnace going til 1st stage is satisfied. Some are kits full of relays on the side of the furnace, others are controlled by the stat with an outdoor thermistor.