Home Improvement

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:

1. 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.

2. 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.

3. 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.

4. 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.

You might need to experiment. What sort of thermostat do you have? Ecobee lets you see one single chart which type of heat is being used and the outside and inside temperatures.

From there you can adjust what temp to skip heat pump and go straight to aux heat so that you aren't wasting time and energy without making your home any warmer. It will automatically switch over of course if no temperature increase is detected within a set amount of minutes (programmed with some sane defaults of course).

I have a dual system and part of it was replaced more recently. I found the part of it that's newer can heat effectively at lower temps. They aren't the same model or anything though.

Idk about that unit specifically, but dual-fuel setups do generally have a way to set their switchover points and contractors are basically always very conservative with where they set them.. I think largely due to them not wanting callbacks on someone's house not heating up fast enough.

You'll have to research your whole setup and figure out where that is.

You can, but the lower you go (usually starting around 30F), performance degrades, with around 15-17F being the lower limit that you can run it in heating mode and still pull heat out of the outside air.

Ideally your aux heat would only be needed on those more extreme days.