Our old flue went through the foundation wall, underground 18' to our chimney. Tree roots got into the underground flue, so we're going with a new dedicated furnace chimney. Stainless Steel double wall pipe is least expensive option, but I'd have to "box it in" with siding to match the siding on our house. A second option is a chimney made with concrete block, but it looks rather industrial (ugly). The traditional brick chimney is the most expensive option, but would be the best looking option.
Is there an efficiency advantage to any of these, a durability advantage?
Thanks for your advice.