I have a double flue chimney. One flue for the fireplace on the first floor. The other flue runs to the basement and has the hotwater heater connected and a filled in port just below that where the old natural gas furnace used to vent. That is now filled in with what appears to be cement. Both holes in the basement flue I believe measure to 6in. Would I be able to remove the current hot water heater from this flue and use this basement flue for a wood furnace or stove?