As many here have said a heat pump (A/C running in reverse) is only effective down to the 40’s and only if it is charged correctly .. running in heat mode the accuracy of the charge is critical to poducing heat efficiently. below the temp where the heat strips (resistance heat) kicks in your power consumption goes WAY up.
Your best option is to make sure you fix any air leaks... to really save $$$ get a Franklin Stove or similar for heat.
Ensure your curtains are thick enough to do the job. On sunny days, open the curtains on the south eastern side to take advantage of solar heat.
Do you have drafts around your entry doors? "Go Medieval," and hang a blanket or tapestry over the portal to block drafts.
Also, apply weather stripping to your doors and windows.
Had we not taken the House, I'd suggest heating rocks over a dung fire and bringing them into your home in iron buckets. Depending on whether the GOP knows how to behave with a modicum of power, we may still need to.
Well, the best way to know for sure is to run a test.
You should have a electric meter on your house.
Start with a quick one day test on each system to test yourself.
1) Ready your electric meter at the start of the day.
For that day, only run your heat pump.
2) At the start of the next day, read your meter.
Calculate how much electricity you used.
For the second day, run only the electric heaters.
3) At the end of the second day, read your meter.
Calculate again how much electricity you used.
Once you have your methodology down good. Run longer tests with different protocols.
Perhaps you want to run the heat pump for the downstairs and the fireplace for the upstairs.
If you monitor your electricity on a daily basis, you can adjust your habits to get the sized bill you desire.
For what it’s worth, I had two heat pumps installed when I built my house about twenty years ago. The local utility company was pushing them with rebates. Since then I have been told by at least two HVAC repair men that they actually cost more to run than a modern HVAC system. I am currently running them without the heat pump component and do appear to be saving money.
Just FYI in case you don't know,
2 X 1500W=3000W=3KW.
3KW x .13=$.39 per hour
x 24hr=$9.36 per day
x 30 days=$280.80.