good point ... except after adding secondary burn to JUCA, efficiency while no where close to Buck 91, should jump up. which should reduce wood consumption substantially. anyways .. been twisting back and fort between keeping JUCA vs Buck 91 ... NO way I'm busting up my chimney ... just got off line with a sheet metal fabricator. seems everything is CAD/CAM .. they input sizes and computer spits out bends.... ball park estimate for a stainless custom duct to fit through existing damper is $150 for 22 gauge (.0025in), $220 for 18 gauge (.0040in). most flex duct in galvanize is 22 gauge.... which thickness stainless do I need? 22 gauge or 18 gauge? say $150 for custom duct & $50 for stainless flex = $200 for all stainless liner, not too bad ... have been burning JUCA for 7 seasons and have never needed to clean chimney. it burns so hot no creosote gets deposited. have inspected chimney every season just to be sure. How often will 8in duct need to be cleaned running Buck 91?