Installed Haier Mini-split system with one outdoor unit and 3 heads inside. Two are 9000btu; one is 12000btu. Total cost with electrician to run the circuit was about $13,000. This was last summer. 2600sf house. We haven't used the oil burner all year except when we had family over the holidays and used our downstairs bedrooms where we didn't bother with mini-splits. They keep us plenty warm, but on that -20 day they used quite a bit of electricity. I'm thinking it might make sense to run the oil burner whenever it falls below -5 or so...depending on oil prices. The oil in my tank was purchased around September at $3.29.