Just got our latest electricity bill. We are up to about 31 kWh per day in a December with several cold spells, and two nights into the single digits. However, our heating system uses propane below 25 degrees F outside, so those nights are not the source of the electricity usage, the cold rest of the time is. One day, I'll figure out how to calculate the propane usage into the energy equation. It would need to be divided into every day that we heat over the whole winter. We've already used one tank this winter so far.
A gallon of propane is 91,690 BTU's = 28.87 kWh x 20 gallons per tank.
= 577.43 kWh per tank
On second thought, the tank is filled to 100 lb (accurate or not) which is 635.26 kWh worth of energy.
As you can see, if we use 3 or 4 tanks per winter, there is a much larger amount of energy being used. That's why the heat pump is so useful. If we use one kWh to heat the house, we get somewhere between 2-4 kWh of heat in the house, because the heat is being moved by, not made from electricity.
Still, pollution wise, the electricity is made largely from coal, whereas the propane has few emissions and is often a waste product from other processes. On the other hand, as I often say, I can make electricity, I can't make propane.