In those rates, I don't know if you factored in that with electric resistance or hydronic bakc-up the HP keep running and generates heat, so the ocmposite COP is >1, WIth a dual fuel, it's either/or, so you don't get to run the heat pump while the furnace is running.
For example, with a Carrier Greenspeed heat pump, it's optimized for capaicity and according to data sheets actually has a lower COP <40F than a Infinity 16 or 19 heat pump. However, it produces a lot of capacity, so it won't need the heat strips nearly as much, so the overall effciency is much much higher.
The power level is increased to provide a somewhat level heat output.
Greenspeed 4 ton added to graph.
It sure limits any significant need for Aux Heat.!
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