Good work! We have a 1920s house also...we were able to gain space by eliminating the chimney as we replaced the old steam furnace (which died right after we moved in, of course) with a direct vent boiler for hot water baseboard (no more stubbed and broken toes during the night!) . Thankfully our house never suffered the mutilation of ductwork for (cold and drafty) "heating" and air cooling, so we cool the house with mini splits to minimize installation damage to the house, and maximize security (thieves use window ac to gain access). All the best in your endeavors!