I have an 18 year old electric furnace and would like to replace it with something more efficient. Should I replace my existing a/c unit with a heat pump or should I look at converting to propane or oil? To complicate things, I have small round ducts (from 30 years ago) that might need to be replaced with regular sized ductwork and vents (apparently these round holes are part of a high pressure system that doesn't work well). Any advice on what I should do??