Switching back and forth from Natural to LP gas depending on season may be difficult. I am no heating or cooling mechanic, but I do know the exit orafices on gas burners vary according to the type of gas you burn. Be careful, because of possibly being overcome with unburnt fumes or carbon monocide. I would not recommend a heating system that used both gases. I would stick to one and rely more on insulation to keep the costs down. Good Luck.