Last fall you guys helped us with the info and direction to install our Keystoker Koker furnace. We did not at that time connect any cold air returns to the Koker but want to do that within the next couple of weeks. We got lots of black dust/soot in our house, not sure if it was from not having a sealed system, or shoveling into the hopper. The Koker is installed next to the forced air propane furnace and using the ductwork to send the heat from the basement to the house, 2000 sq/ft, 2 story, built in 1873. It heated the entire house very well, was toasty warm all winter but sick of the black coal layer even on the second story. Can anyone offer advice?