After just a few uses I am very impressed with the burn efficiency. It appears the efficiency comes from a good draft, air control, direction of the air and the reburn tubes. I used 6" triple wall stainless chimney and double wall stove pipes straight up the interior. The large firebox is great as my use is supplemental to get BTUs quickly. Very heavy and appears well constructed at a reasonable price. The order and 3 day delivery system thru myfireplaceproducts was flawless.