Cost of heating...
Heat pumps are the most efficient and cleanest form of heating you can have for home heating currently. The reason for their efficiency is that they dont create heat rather transfer heat between inddor and outdoor through the refrigerant.
Heat pumps are 300 to 400+ % efficient which means for $1 you spend you get $3 to $4 of heating with heat pumps in Auckland.
Here is a graph showing comparison of heating costs.