One place that many homeowners forget to check off their list during their weatherization overall is the flue for their fireplaces. When the fireplace is in use it serves its purpose but when it is dormant it can be a big source of cold air infiltration into their home in the winter.
One way to prevent air infiltration from the flue is installing glass doors around the fireplace. This will allow your customers the capability to close the doors when the fireplace is not in use and help prevent cold air from entering the house. Let your customers know that the flue can be a large source of air infiltration and actions need to be taken to stop it.