I am ordering my new Hitzer 503 today to replace my Firepower furnace (cracked heat exchanger after 26 years of faithful coal service). This forum helped me make up my mind - I like the looks & features of the 503 better than the equivalent Harman (which at my shopping choices is $1,000 more). Question #1 has to do with flue installation - running SS flex a few feet past the damper (sealing the rest of the damper opening) and then letting the existing 8" x 13" terra cotta do its thing vs. running flex the entire length (19' up from damper). I prefer the first for cost reasons - will only burn good, hard coal (no wood), so ash around the sealed damper should not be a problem - Hitzer advised this meets code and is OK in the situation I describe. Any contrary thoughts, other than a full liner is easier to clean? Question #2 - for those who burn a 503 - I would appreciate any advice on use of and the relationship between the bottom and top combustion air dampers. Please feel free to contact me off-list, if you prefer ([email protected]). Thanks.