I live in a pre-revolutionary Dutch Colonial. The main floor walls are 18" deep sandstone with plaster interior (over animal hair, and random old newspaper). The sandstone has great thermal mass so that the house is impervious to sudden temperature changes. However, from December to mid April it becomes an icebox, as the stone adapts to the outside temps.
Anyone have any ideas that won't impact the character of the house? Keeping warm without changing the character is really the challenge. I appreciate your thoughts and responses.