For fireplace chimneys which have been rarely or never ever used, inflate a Chimney Balloon inside the chimney to prevent the air leaks. Buy it directly from the company. Partially inflate the balloon by mouth or with a pump, then stick it in to the chimney and blow it up https://reducefranchiseenergybills.wordpress.com/2024/08/22/how-to-reduce-franchise-energy-bills-with-sustainable-practices/