The majority of the windows have triple track storm windows. At least they're not drafty but I know I lose heat through the glass. Third floor windows are energy efficient ones. I couldn't bear (or afford) to replace the first and second floor windows. They're all handmade, beautiful natural chestnut woodwork, and, in most cases, original wavy glass. It is bright and cheerful here with the sun streaming in. If I get chilly I can put on one of those warm English wool sweaters I always buy when I go on holiday.