Gas furnaces are FAR more efficient than their electric resistance heating or even heat pump counterparts. Not to mention that a simple gas burner works with no moving parts (other than the solenoid valve) for decades with no maintenance, while heat pumps, in my experience, are far more troublesome than regular HVAC units, and still have to fall back to grossly inefficient resistance heating (even in a normal central Texas winter!) when temps dip below freezing. (One great thing about my parents moving several years back was leaving their $400-1000 annual heat pump repair bills behind. It wasn't just a bad unit - it was the third heat pump they'd had, and all (even from different mfrs!) were similarly troublesome, esp. for heating.)