Good evening! A winter cottage with large glass surfaces does pose a challenge for heating, especially in extreme cold like -20°C. To tackle this, you'll need an efficient heating system such as underfloor heating, radiant heaters, a wood stove or fireplace, or modern heat pumps. Additionally, installing proper insulation around the glass, like double or triple-glazed windows, can significantly reduce heat loss. Fortunately, there are plenty of options available today.