I am gas, but the system is the same. Just the cost of fuel is different. I understand Propane costs roughly 6 times more than Natural gas per BTU so you would need to factor that in. Mini Splits lose efficiency from 40 degrees and at 20 lose drastically. So mostly you would have to guess how many cold days you have below 20 that a system would make up for and handle hot water. I think in your odd case keeping oil might be the most cost effective idea.