Venting issue

My 200 year old chimney has been restored with "Golden Flu" resulting in a 6 inch flu which is great for wood stoves but too small for "direct vent" gas stoves and too large for "B vent gas stoves. Suggestions?

Most direct vent gas stoves can be run into a link kit which is a 4" liner down the middle and it uses the space around it for the fresh air.

For a B-Vent stove you could drop an alum liner down if the unit is approved for that. Alum liners are cheap.

Don't burn wood in the open fireplace (if you have one). It will smoke back like mad with only a 6" flue.

And what would be the result if I used a B-vent stove with the 6 inch flu?

Not sure, ask the manufacturer or check the manual. We don't sell B-Vent fireplace around here anymore. Dropping a 4" alum gas liner down the flue would not be very expensive anyway. You could prob find a liner kit with a cap for $300-$500