The real question is what the total cost of ownership and what is the payback period? Also there are regional climate differences that have to deal with very large temperature swings as well as very old poorly insulated houses. investing hundreds of thousands to re-insulate one's house, replace all the windows, excavate the heat sink and dispose of a furnace that is already working, so that one can buy a heat pump at greater costs than a furnace to achieve efficiency improvements that barely pay for themselves over thirty years when the same amount of money can be spent elsewhere. if it were such a great idea it would have already been done.