I am looking to replace my hvac system with a heat pump and a backup furnace. One installer recommended an electric backup and the other a propane backup. I currently have a 20 yr old 80% propane furnace. But I am concerned that an all electric system would be very expensive when its too cold for the heat pump to do its job. I live in Indianapolis IN, so we do get some cold days in the winter. Right now I spend about $1500 / year on propane , so getting rid of the propane all together would be a savings. Does anyone recommend one system vs the other?