Ashful
Minister of Fire
The gas furnace is more than 20 years old. I have no idea what the requirements are to vent a gas furnace (natural gas, hot water furnace with old fashioned radiators). Anyone have any ideas? I'd love to be able to use the interior chimney with a liner for this kitchen cook stove.
Maybe call the original installer? His sticker should be on the side of the furnace. 20 years is not that long, chances are he's still in business. Most installers only carry / install a few furnace models, and so he probably knows the requirements for your model inside and out.