using the gas
C = ( 3,600,000,000 btu ) ( 1 therm / 10,000 BTU) ( 1 / 0.95 ) ( $ 1.45 / therm) + $ 3,000
C = $ 552,474
using the hvac unit
c = ( 3,600,000,000 btu ) ( 1 kwh / 3412.14 btu ) ($ 0.042 / kwh )
c = 44312.36
plus a 2% fuel recovery
C = 44312.36( 1.02) = $ 45199
so its much cheaper to use the electic hvac unit than using the gas furnace