It's buried in the article, but the 77% number seems to be based on resistance heating instead of heat pumps:
> the annual energy bill to operate a standard gas furnace/AC combination is about $633 a year. With a heat pump, she said, it would likely be $609 to $718 annually, depending on the heat pump technology chosen and its configuration.
> the annual energy bill to operate a standard gas furnace/AC combination is about $633 a year. With a heat pump, she said, it would likely be $609 to $718 annually, depending on the heat pump technology chosen and its configuration.