My neighbor had a chimney fire about 5 weeks ago. They're having the entire stove pipe and chimney pipe run replaced. Stove had about 6 feet of single wall stove pipe then double wall chimney pipe for 20+ feet. Their current plan is to use double wall stove pipe for the 6 foot section then new chimney pipe. I think thy will lose a lot of heat transfer with the double wall. Looking for thoughts from folks with knowledge.