My furnace is no longer safe to use. There are a lot of furnaces out there and I need help finding a reliable and fuel efficient natural gas furnace brand. Please tell me your good or bad experiences with you furnace brand. Also my ducting looks like the old white clothes dryer ducting. It is not insulated. Does this need to be replaced or is it okay. It had to have passed inspections as it is the house original. I live in a northern climate and I seems like I am heating my crawl space. Thanks!