I have a heat pump that is set to 68°. I also have an oil-fueled boiler is set to 55°.

When the outside temps drop too much below 20°, the heat pump seems to struggle to keep up, so that's when I shut it off and turn the boiler up to 65°.

Even as high as electricity is right now, the heat pump seems to be saving vs. oil. I'm expecting that I'll have to burn more oil for heat this week, though.