It depends. In my 2016 build, my heat/cooling is heat pump, my hot water is gas (so is my stove). But I’m in Seattle where heat pumps don’t need a backup, and electricity is fairly cheap. A gas furnace would seem like a waste even though we have a gas line, although we do have a gas fireplace that we use for heat more often than the heat pump (which we only use when it is really cold).