A gas furnace would require electricity. You need electricity to ignite and exhaust most natural gas heating. There are vent-free options. Not common for those to be installed and back to having your own option for backup power. Which can be propane or gasoline.
The amount of electricity a gas furnace requires is trivial and not really relevant to this discussion. A heat pump requires many orders of magnitude more electricity. A 10kwh battery could power a gas furnace and a water heater electrically for a year.
Now this natural gas house has a 10kwh whole house battery backup too? Hope your refrigerator can also last a year off that battery pack (oh wait it's a ac compressor too!),
Heat Pump for heat, Heat Pump water heater is the future for new home builds. Buy a portable generator, a 10kwh gasoline generator is <$1,000 USD and 1/10th the price of a 10kwh batter pack. Problem solved.
