I had one of these in my fireplace 40 years ago. Look familiar? The same OLD technology is still used in many of our stoves. Round tubes with air blowing through them! You would think in 40 years, someone would start using extruded aluminum finned tubing at least if not a completely rethought heat transfer scheme. Some do, I know but not many.
http://www.woodlanddirect.com/Firep..._a_7c1360010&gclid=CM7uh8PUq8MCFYgAaQodq0kAdg
http://www.woodlanddirect.com/Firep..._a_7c1360010&gclid=CM7uh8PUq8MCFYgAaQodq0kAdg