[BroadHopper]

I know the efficiency of my condensing gas boiler and how much it cost per btu.
I also know the efficiency of my split system and how much it cost per btu.

The efficiency of the mini-split drops as the outside temperature drops. I find the cross-over point. This is where I switch to the more efficient heat.

Also, the gas boiler heats up a cold space rather quickly compared to the split system. So I use gas to increase the temperature and switch to the split.

An engineer told me that a split is inefficient when trying to raise the temperature of a cold home. It is efficient in maintaining a set temperature.

So do some research and use your judgment.