I think you're getting some really bad advice. It really sounds like the guys is talking about an air-source heat pump. These basically stop working when temps get much below freezing. If a geo system is properly sized and you have a decent heat source/sink you should never need backup unless something is broken. Our system has electrical resistance backup which is disconnected because we never need it. Though we try to heat with wood when we're home we have run out of wood before and our geo system has never failed to keep our house warm even when night time lows drop into the single digits. I think you should seek other advice before you make a decision.