It all depends on how efficient your heat pump is and how efficient your gas boiler is. Gas is not always most efficient. In my house, down to about 40F my heat pumps are more efficient in terms of monthly bill. Below 40 gas is cheaper. I have a 95% efficient tankless boiler and SEER 20 mild temp heat pumps. Your millage may vary, if you had a 80% efficient boiler heat pumps are going to be way better.
It all depends on how efficient your heat pump is and how efficient your gas boiler is. Gas is not always most efficient. In my house, down to about 40F my heat pumps are more efficient in terms of monthly bill. Below 40 gas is cheaper. I have a 95% efficient tankless boiler and SEER 20 mild temp heat pumps. Your millage may vary, if you had a 80% efficient boiler heat pumps are going to be way better.