Pellet stove -wood pellets $ 200 / ton $ 1.52 Air-to-air electric heat pump $ 0.09 / KwH $ 1.60 Natural gas forced-air furnace $ 1.33 / therm $ 1.66 LP gas H.E. forced-air furnace $ 1.83 / gallon $ 2.51 Electric resistance heat $ 0.09 / KwH $ 2.64 LP gas older forced-air furnace $ 1.70 / gallon $ 3.09