I’m on mobile and tbh don’t have time to dig into this too much, but I think you would do well to calculate the point of optimum efficiency for your specific scenario. I am in a similar scenario and hope to put together a spreadsheet that I could share if it doesn’t already exist elsewhere, but here is what I would do:
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Find out if your heat pump IOM specifies the minimum ambient temperature before electric auxiliary heat kicks in (sometimes called “em heat” or emergen heat). Electric heat will always be the most expensive source of heat, so you should use oil heat when temperatures drop below that.
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Look up the peak electric rate (in $/kW-hr) for your utility company. Use this to calculate the cost, per hour, to run your heat pump in all temperatures tabulated in your link. This will tell you how expensive it is to run your heat pump in a worst-case scenario.
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Calculate the cost to run your boiler, per hour. This is where you will have to do your own homework on efficiency of your boiler, rate of consumption, and cost of oil in your location. Hard to say if the boiler will run at full capacity or part load, but most are capable of running between 20-100% of nameplate capacity (5:1 turn-down). Summarize your findings into a coat to run your boiler per hour.
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When the answer for #2 exceeds the answer for #3, you’ve identified your switch point! Note that this relies on a number of assumptions, like that the heat pump is running full capacity.