Once the temp gets under 40 degrees F, there is no more heat for the heat pump to pump. The resistance heater strips kick in. Your house is warm, but you can use your electric meter as a buzz saw.
In a Minnesota winter you would be running resistance heat pretty much from October through March. Hope they don’t outlaw fireplaces - gonna need them.
“Once the temp gets under 40 degrees F, there is no more heat for the heat pump to pump. The resistance heater strips kick in”
Yes, if your experience is limited to circa 1987 heat pumps that sounds about right.
Around here premium systems installed in new subdivisions are starting to switch over around -5°F.