Yeah, you can indeed do it that way, but you can also wire it with an outdoor stat to switch the Y signal from the heatpump to the furnace at about 30º F. In fact, there is several different ways it can be done with a regular heatpump stat and the right controls depending on what you want to do with the system. We see lots of duel fuel around here and rarely are two in a row wired the same way.
Originally posted by phosgene
IMHO a HP stat will not work. You need a specified "dual fuel" thermostat, that will lock out the gas furnace when the heat pump operates. It is not like a heat pump with electric supplemenatal that can operate at the same time. With duelfuel once supplemental or aux comes on it will finish the heating cycle also if it is wired for aux to come on during defrost, aux will finish the heating cycle.