Have you looked into Mini-Splits? A central system with two air handlers will be complicated, expensive and can be problematic if the ducting is not properly designed.They told me every single thing was covered, no questions asked for the 1st 12 years after install. Diamond installer or something... We're currently paying about $2400/yr for electric and $7k a year for oil. House is only about 1300sqft and was remodeled about 10 years ago, so semi modern drywall and windows
What are the range of estimates? Are they similar in equipment?