My stove has a large fan for drawing out cooking gases, which it does most effectively. However, the rest of the time it just sits there letting cold air in. As a consequence, that part of the kitchen is often cold, especially on windy days. When the wind blows from the North, the South side of the house, where the fan is, experiences negative pressure. This is enough to pull open the flaps on the fan, and draw out warm air from the house.
Some of these things are harder to fix than others, but for a start I decided to insulate the duct from the fan to the outside. It is the black box in the picture. The wavy dark line along the bottom is condensed moisture for it being colder than the dewpoint of the house.
I started by insulating behind the fan and the duct, with rigid and spray foam insulation.